The project (WASP) leading to this publication, has received funding from the European Union&#8217;s Horizon 2020 Research and Innovation Program under grant agreement No. 825213.

1. Operation of the FIRA Oven
NOTE: A schematic of the FIRA oven, developed in-house, is shown in Figure 1A. The FIRA oven is composed of an array of six near-infrared halogen lamps (peak emission at wavelength of 1,073 nm) with an illumination power of 3,000 kW/m2 and a total output power of 9,600 kW. A hollow aluminum body provides an effective water-cooling system and it in turn allows rapid thermal energy dissipation (within seconds). It is kept in a nitrogen glovebox, and N2 is continuously flowed through the chamber via a gas inlet to keep it under an inert atmosphere, except during annealing. O2 can also be introduced when annealing metal oxide films to promote oxidation.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61730/61730fig01.jpg" /> 
Figure 1: (A) Schematic showing cross-section of the FIRA oven. The oven chamber is continuously cooled by water flowing through the case and kept under an N2 atmosphere. (B) Picture of the FIRA oven. <a href="https://www.jove.com/files/ftp_upload/61730/61730fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61730/61730fig02.jpg" /> 
Figure 2: Interface of the FIRA software.&#160;The panel on the left shows the temperature profile, which displays the set point (input program), oven temperature, and pyrometer (substrate surface) temperature. The desired annealing program is inputted on the table on the right. <a href="https://www.jove.com/files/ftp_upload/61730/61730fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol>
	<li>Programming of annealing cycles
	<ol>
		<li>Connect the FIRA oven to a computer, from which it can be controlled via a guide user interface (Figure 2) on an in-house software. Based on the experiment, select full-power mode or PID (proportional-integral-derivative) mode. In full-power mode, the IR lamps are either completely on or off, whereas in PID mode, the oven is held at a specific temperature for a certain amount of time by intensity modulation.</li>
		<li>Ensure Table is selected on the Table/Manual toggle and input a timebase that is longer than the total duration of the annealing and cooling processes.</li>
		<li>Full-power mode: Input the times at which the lamps should be on or off in the table on the right of the interface. In this way, single pulses as well as annealing cycles can be programed, allowing control of the pulse length and frequency. This is suitable for films that can be rapidly annealed, or for substrates that cannot tolerate sustained heating (e.g, ~1.5&#8211;2 s for perovskite films).</li>
		<li>PID mode: Input the time and temperature at which the oven should be irradiated in the table. Similar to the working principle of a traditional hotplate, the intensity of the heating source can be modulated. This is suitable for films that typically require longer annealing times (e.g., 15 min at 100 &#176;C for TBAI).</li>
		<li>Data acquisition: Download the temperature profile displayed on the left of the interface as a .txt or spreadsheet file by right-clicking on the profile and then click on Export File. 
		NOTE: The software is used for both data acquisition and system control, where the main raw data acquired is the temperature profile. On the temperature profile (Figure 2), the input program is represented by the &#8220;set point&#8221;. The oven temperature (measured by a K-type thermocouple) and substrate temperature (estimated by a pyrometer) are displayed in real time, giving insight into the thin film crystallization conditions. Please note that the oven temperature does not scale directly with traditional hot plate temperatures as the thermocouple is also directly exposed to IR radiation. Rather, it serves as a reference point for comparison between different FIRA annealing parameters.</li>
	</ol>
	</li>
	<li>General annealing process
	<ol>
		<li>Deposit the precursor via a suitable solution process: spin-coating26, dip-coating27, or doctor-blading28.</li>
		<li>Transfer the substrates into the FIRA oven chamber and close the oven lid. Ensure that nitrogen flow into the chamber is turned off by closing the gas inlet valve.</li>
		<li>Start and stop the annealing by clicking on START table and STOP table on the computer. Alternatively, connect the FIRA oven to a foot pedal, which can also be used to start and stop the program. As a result, annealing can be carried out without removing one&#8217;s hands from the glovebox, allowing for a much smoother and synchronized process.</li>
		<li>When the oven temperature reaches room temperature, remove the substrates from the oven chamber.</li>
	</ol>
	</li>
</ol>
2. MAPbI3 Perovskite Film Synthesis and Optimization on FTO Glass
<ol>
	<li>Perovskite Solution Preparation
	<ol>
		<li>Dissolve methylammonium iodide in anhydrous DMF:DMSO 2:1 v/v to obtain a 1.9 M solution.</li>
		<li>Add an equimolar amount of PbI2 to the solution and dilute with anhydrous DMF:DMSO 2:1 v/v to give a 1.4 M methylammonium lead iodide precursor solution. Heat at 80 &#176;C until complete dissolution and cool to room temperature. 
		NOTE: The solution is prepared and stored in an argon glovebox. The protocol can be paused here.</li>
	</ol>
	</li>
	<li>Perovskite film synthesis
	<ol>
		<li>Use FTO coated glass substrates of 1.7 cm x 2.5 cm.</li>
		<li>Clean the substrates via successive sonication in cleaning soap (2 vol % in deionized H2O), acetone and ethanol for 15 min each, then dry them with compressed air.</li>
		<li>Treat the substrates under UV/ozone in a plasma cleaner for 15 min.</li>
		<li>Input the desired annealing program as per section 1.1.</li>
		<li>Blow the substrate surface with a nitrogen gun to remove dust and other impurities.</li>
		<li>Spin-coat 50 &#181;L of the perovskite precursor at 4,000 rpm for 10 s, with an acceleration of 2000 rpm&#183;s-1.</li>
		<li>Immediately after deposition, transfer the substrate to the FIRA oven for annealing at a range of pulse times as desired (0&#8211;7 s used herein, optimized pulse is 2 s). Start the inputted annealing program by pressing START on the software or stepping on the foot pedal. A color change from yellow to black should be observed, indicating the formation of a 3D perovskite structure.</li>
		<li>Remove the substrate when the oven temperature reaches 25 &#176;C.</li>
		<li>Store the annealed films in a dry air box. 
		NOTE: The FIRA oven and the spin-coater are placed in the same nitrogen glovebox such that solution deposition and annealing can be carried out smoothly and under an inert atmosphere.</li>
	</ol>
	</li>
	<li>Material characterization
	<ol>
		<li>Capture optical images on a polarizing microscope equipped with a xenon light source and infinitely corrected objectives of 10x and 50x.</li>
		<li>Record absorbance spectra simultaneously with an optical fiber integrated into the microscope set-up and connected to a spectrometer (spectral range 300&#8211;1,100 nm). 
		NOTE: The above characterization can be done immediately after annealing, allowing for rapid screening of film quality. The measurements are taken in ambient air and temperature. More in-depth characterization such as scanning electron microscopy (SEM) and X-ray diffraction can be subsequently carried out (see section 3.7).</li>
	</ol>
	</li>
</ol>
3. FCG perovskite solar cell processing
<ol>
	<li>Substrate preparation and cleaning
	<ol>
		<li>Etch one side of the FTO glass substrates with Zn powder and 4 M HCl.</li>
		<li>Clean substrates via successive sonication in cleaning soap (2 vol % in deionized H2O) for 30 min and isopropanol for 15 min, and dry with compressed air.</li>
		<li>Treat under UV/ozone in a plasma cleaner for 5 min.</li>
	</ol>
	</li>
	<li>Compact TiO2 layer
	<ol>
		<li>Heat FTO glass substrates to 450 &#176;C on a sintering hot plate and keep them at this temperature for 15 min before solution deposition.</li>
		<li>Dilute 0.6 mL of titanium diisopropoxide bis(acetylacetonate) and 0.4 mL of acetylacetone in 9 mL of EtOH to give the precursor solution.</li>
		<li>Deposit the solution via spray pyrolysis with oxygen as the carrier gas (0.5 bar) at 45&#176; and a distance of ~20 cm. Leave an interval of 20 s between each spraying cycle.</li>
		<li>Leave the substrates at 450 &#176;C for 5 min more, then cool to room temperature. This gives a compact TiO2 layer of ~30 nm. 
		NOTE: The protocol can be paused here. If the next step is not carried out immediately, re-sinter the substrate at 450 &#176;C for 30 min before deposition of the mesoporous-TiO2 layer.</li>
	</ol>
	</li>
	<li>Mesoporous-TiO2 layer
	<ol>
		<li>Make a precursor solution by diluting TiO2 paste (particle size 30 nm) in EtOH at a concentration of 75 mg/mL. Stir the solution with a magnetic stirrer bar until complete dissolution.</li>
		<li>Spin-coat 50 &#181;L of the solution at 4,000 rpm for 10 s, with a ramp of 2,000 rpm&#183;s-1.</li>
		<li>Program an annealing cycle of 10 pulses, 15 s on and 45 s off in the table on the software.</li>
		<li>Place the substrates in the FIRA oven, and anneal under full power mode with the above annealing cycle by pressing Start Table or stepping on the foot pedal. This yields a 150&#8211;200 nm layer.</li>
		<li>Remove the samples when the oven temperature reaches 25 &#176;C. 
		NOTE: Ensure that the oven is at room temperature or below before starting annealing. With the above cycle, the oven temperature reaches ~600 &#176;C during annealing.</li>
	</ol>
	</li>
	<li>Perovskite layer
	<ol>
		<li>Make a solution of formamidinium iodide (1.12 M), PbI2 (1.4 M), CsI (0.21 M) and GAI (0.07 M) in anhydrous DMF:DMSO 2:1 v/v.</li>
		<li>Spin-coat 40 &#181;L of the solution at 4,000 rpm for 10 s.</li>
		<li>Program an annealing step of 1.6 s on full power mode on the software (this reaches ~90 &#176;C).</li>
		<li>Transfer the substrate to the FIRA oven and start annealing by pressing Start Table or stepping on the foot pedal. The surface should turn from yellow to black.</li>
		<li>Leave the samples in the oven for an additional 10 s for cooling before removal.</li>
	</ol>
	</li>
	<li>Tetrabutyl ammonium iodide (TBAI) post-treatment (optional)
	<ol>
		<li>Dissolve 3 mg of tetrabutyl ammonium iodide in 1 mL of isopropanol.</li>
		<li>Spin-coat the solution at 4,000 rpm for 20 s.</li>
		<li>Program an annealing step at 100 &#176;C for 15 min using PID mode.</li>
		<li>Transfer the substrate to the FIRA oven and anneal with the above program. Cool to 25 &#176;C before the next step.</li>
	</ol>
	</li>
	<li>Hole transporting material and top electrode
	<ol>
		<li>Dissolve spiro-OMeTAD in chlorobenzene (70 mM) and add 4-tert-butylpyridine (TBP), Lithium bis(trifluoromethylsulphonyl)imide) (Li-TFSI, 1.8 M in acetonitrile) and Tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)-cobalt(III) Tris(bis(trifluoromethylsulfonyl) imide) (FK209, 0.25 M in acetonitrile) such that the molar ratio of the additives with respect to spiro-OMeTAD are 3.3, 0.5, and 0.03 for TBP, Li-TFSI, and FK209 respectively.</li>
		<li>Deposit 50 &#181;L of the solution at 4,000 rpm for 20 s under dynamic spin-coating, adding the solution 3 s after the start of the program.</li>
		<li>Leave it to oxidize overnight in a dry air box.</li>
		<li>Deposit 80 nm of gold via thermal evaporation under vacuum. Use a shadow mask to pattern the electrodes.</li>
	</ol>
	</li>
	<li>Photovoltaic device testing and material characterization
	<ol>
		<li>Take photovoltaic measurements using a solar simulator equipped with a xenon arc lamp and a digital source meter. Specify the active area of the device with a black, non-reflective metal mask (0.1024 cm2 used herein). Measure the current-voltage curves under reverse and forward bias at a 10 mV/s scan rate under AM 1.5 G irradiation.</li>
		<li>Take X-ray diffraction patterns with a diffractometer in reflection-spin mode, using Cu K&#945; radiation and a Ni &#946; filter.</li>
		<li>Take scanning electron microscope images at an acceleration voltage of 3 kV.</li>
	</ol>
	</li>
</ol>
4. MAPbI3 films on ITO-PET substrate
<ol>
	<li>Cut ITO-PET and microscope glass slides into pieces of 1.7 cm x 2.5 cm.</li>
	<li>Clean the glass slides and ITO-PET as per steps 2.2.2&#8211;2.2.3.</li>
	<li>Attach the ITO substrates onto the glass slides with double-sided tape, ensuring they are as flat as possible.</li>
	<li>Prepare the MAPbI3 precursor as described in section 2.1. Blow the substrate surface with an N2 gun before spin-coating the solution and annealing the film with FIRA, as per steps 2.2.5&#8211;2.2.8, with a pulse time of 1.7 s.</li>
	<li>Carry out material characterization as described in sections 2.3 and 3.7.</li>
</ol>

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S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morphology+of+polymer/fullerene+bulk+heterojunction+solar+cells.">Morphology of polymer/fullerene bulk heterojunction solar cells.</a> Journal of Materials Chemistry. 16 (1), 45-61 (2006).</li><li>Paquin, F., Rivnay, J., Salleo, A., Stingelin, N., Silva, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multi-phase+semicrystalline+microstructures+drive+exciton+dissociation+in+neat+plastic+semiconductors.">Multi-phase semicrystalline microstructures drive exciton dissociation in neat plastic semiconductors.</a> Journal of Materials Chemistry C. 3 (41), 10715-10722 (2015).</li><li>Diao, Y., Shaw, L., Bao, Z., Mannsfeld, S. C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morphology+control+strategies+for+solution-processed+organic+semiconductor+thin+films.">Morphology control strategies for solution-processed organic semiconductor thin films.</a> Energy &amp; Environmental Sciences. 7 (7), 2145-2159 (2014).</li><li>Slotcavage, D. J., Karunadasa, H. I., McGehee, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Light-induced+phase+segregation+in+halide-perovskite+absorbers.">Light-induced phase segregation in halide-perovskite absorbers.</a> ACS Energy Letters. 1 (6), 1199-1205 (2016).</li><li>Jiang, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+passivation+of+perovskite+film+for+efficient+solar+cells.">Surface passivation of perovskite film for efficient solar cells.</a> Nature Photonics. 13 (7), 460-466 (2019).</li><li>Yang, W. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Iodide+Management+in+formamidinium-lead-halide-based+perovskite+layers+for+efficient+solar+cells.">Iodide Management in formamidinium-lead-halide-based perovskite layers for efficient solar cells.</a> Science. 356 (6345), 1376-1379 (2017).</li><li>Almadhoun, M. N., Khan, M. A., Rajab, K., Park, J. H., Buriak, J. M., Alshareef, H. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=UV-Induced+ferroelectric+phase+transformation+in+PVDF+thin+films.">UV-Induced ferroelectric phase transformation in PVDF thin films.</a> Advanced Electronic Materials. 5 (1), 1800363 (2019).</li><li>Hooper, K., Smith, B., Baker, J., Greenwood, P., Watson, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spray+PEDOT:PSS+coated+perovskite+with+a+transparent+conducting+electrode+for+low+cost+scalable+photovoltaic+devices.">Spray PEDOT:PSS coated perovskite with a transparent conducting electrode for low cost scalable photovoltaic devices.</a> Materials Research Innovations. 19 (7), 482-487 (2015).</li></ol>

The authors have nothing to disclose.

Figure 9 shows the general process of perovskite film annealing with FIRA.
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/61730/61730fig09.jpg" /> 
Figure 9: Schematic representation of perovskite film processing with FIRA.&#160;The wet film is deposited from the solution by spin-coating and subsequently transferred to the FIRA oven for annealing in ~2 s, giving the black perovskite stable phase. <a href="https://www.jove.com/files/ftp_upload/61730/61730fig09large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
In the solidification process of a thin film from the solution, the desired final shape will depend on the application: films in energy devices for photocatalysis, battery electrodes, and solar cells can have different morphologies30,31,32,33. Therefore, identifying the optimal parameters for each substrate and wet film interface is a critical step in the protocol to follow. Typically, for PSCs we expect to have shiny and smooth films in order to minimize defects and to enhance the photophysical properties such as charge transport of carriers to give null non-radiative recombination34,35,36. For thin film processing, the main parameters are pulse time, the number of pulses, and the irradiation temperature, which are a balance between forming the desired morphology while being as rapid and energy efficient as possible. Insufficient energy would lead to incomplete solvent evaporation or crystallization, while excess energy would lead to degradation of the material. Therefore, it is crucial to systematically vary the annealing parameters and analyze the resulting film quality (as detailed in sections 2.2, 2.3, and 3.7) to find the optimal parameters for each thin film/substrate combination. Once this is completed, thin films can be synthesized rapidly and reliably. The method relies on its accuracy, for example, the minimum pulse time is 20 ms, allowing one to finely control the temperature ratio for crystal growth. Besides, one can have a wide window for optimization, aided by the data collection of images and absorption spectra for optical and morphological screening.
The FIRA method is still in development, and, as its name implies, it is currently based on IR irradiation. However, the latest version of FIRA includes UV-A radiation generated from a separate metal-halide lamp source. UV and IR can be used for combined wavelength photonic annealing and curing, providing additional functionality. For example, semiconductor curing with FIRA is a straightforward way to improve the wettability of substrates. Additionally, for a multi-layered approach in crystal growth, this selective wavelength annealing can be adapted depending on the material, and the pulse can be modulated depending on the desired shape16,32,37. Current investigations include annealing of an ITO electrode and a mesoscopic-TiO2 layer on paper (the latter using mixed IR/UV annealing, see Supplemental Figure 5 in the supplementary information). As shown in Supplemental Figure 6, a perovskite film can be successfully deposited on the FIRA-annealed ITO/TiO2 stack. This can be applied to a wide range of substrates and thin films in the future.
So far, the FIRA method is limited to the annealing of wet films that can be deposited via solution processes. It depends on the capability of the deposition method, and this is governed by solvent engineering and multi-layered growth based on solutions with approaching solvent polarities. Optimization is also required for each thin film as this is a novel method without a lot of previously reported protocols in literature, which may be time-consuming. Additionally, although FIRA can be used for flexible substrates such as PET and paper as there is rapid cooling from the case, a good contact between the substrate and the oven chamber must be ensured to avoid substrate melting. This may be difficult since flexible substrates are easily bent during processing, but this may be improved by attaching the substrates on a thin glass slide to ensure that they are completely flat and to allow ease of manipulation. However, it is important to note that the absorption of the film will change as the material transitions from non-absorbing (wet NIR-transparent perovskite precursor material) to dry (NIR-absorbing black perovskite) and this additional absorption can contribute to the damage of the substrate38.
Despite these limitations, FIRA still presents many advantages in comparison to the antisolvent method. Firstly, thin films can be synthesized much quicker. For example, the perovskite is formed in &#60;2 s while the mesoporous-TiO2 layer is formed in only 10 min, much shorter than the hours required in the conventional method. The elimination of the antisolvent and the shorter annealing times also mean that there is a much lower energetic and financial cost. Life cycle assessment (Figure 10) of the perovskite synthesis process shows that FIRA presents only 8% of the environmental impact and 2% of the fabrication cost of the antisolvent method. Additionally, it is compatible with flexible and large-area substrates. A total area of 10 x 10 cm2 can be irradiated at one time, and it has already been shown that devices of 1.4 cm2 active area as well as films of 100 cm2 can be synthesized this way. Finally, it is highly reproducible, versatile, and adaptable to fast throughput roll-to-roll manufacturing, as the deposition and annealing steps are carried out continuously in one place in a synchronized and smooth process.
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/61730/61730fig10.jpg" /> 
Figure 10: A comparison of the relative cost and environmental impact of FIRA and anti-solvent methods determined by life cycle assessment.&#160;GWP = Climate change [kg CO2 eq], POP = Photochemical oxidation [kg C2H4 eq], AP = Acidification [kg SO2 eq], CED = Cumulative energy demand [MJ], HTC = Human Toxicity, cancer effects [CTUh], HTNC = Human Toxicity, non-cancer effects [CTUh], ET = Freshwater ecotoxicity [CTUe]. Reproduced with permission from12. <a href="https://www.jove.com/files/ftp_upload/61730/61730fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Current investigations on FIRA are focused on optimization for thin film synthesis on flexible substrates such as paper and PET, as well as for the synthesis of other key component layers of PSCs such as the SnO2 compact layer, or carbon and ITO electrodes. Furthermore, the next step is to fabricate high-performing devices of &#62;5 cm2. Therefore, it can be said that FIRA represents a step toward an environmentally friendly and cost-efficient way to manufacture large-area, commercial PSCs.

Since their inception in 2009, solar cells based on lead halide perovskites have demonstrated unprecedented growth, with power conversion efficiencies (PCE) increasing from 3.8%1 to 25.2%2 in just over a decade of development. Recently, there has also been interest in the development of perovskite solar cells (PSCs) on flexible substrates such as polyethylene terephthalate (PET) as they are lightweight, cheap, applicable to roll-to-roll manufacturing and can be used to power flexible electronics3,4. In the past decade, the PCE of flexible PSCs has improved significantly from 2.62% to 19.1%5.
The majority of the current processing methods for PSCs involve deposition of the perovskite precursor solution, addition of an antisolvent (AS) such as chlorobenzene to induce nucleation and finally thermal annealing to evaporate the solvent and promote crystallization of the perovskite in the desired morphology6,7,8,9. This method requires moderate amounts of organic solvent (~100 &#181;L per 2 x 2 cm substrate) that is typically not reclaimed, is difficult to apply on large-area substrates and is not always reproducible. Additionally, the perovskite layer requires annealing at &#62;100 &#176;C for up to 120 min while the mesoporous-TiO2 electron transporting layer requires sintering at 450 &#176;C for at least 30 min, which not only leads to a large electronic cost and a potential bottleneck in the eventual upscaling of PSCs, but is also incompatible with flexible substrates which typically cannot sustain heating at &#8805;250 &#176;C10,11,12. Alternative manufacturing methods must, therefore, be found to commercialize this technology3,13,14.
Flash infrared annealing, first reported in 201511, is a low-cost, environmentally friendly and rapid method for the synthesis of compact and defect-tolerant perovskite and metal oxide thin films that eliminates the need for an antisolvent and is compatible with flexible substrates. In this method, freshly-spin-coated perovskite films are exposed to near-IR radiation (700&#8211;2,500 nm, peaking at 1,073 nm). Both TiO2 and perovskite have low absorbance in this region, whereas FTO is a strong NIR absorber and rapidly heats up, evaporating the solvent and indirectly annealing the active material11,15. A short 2 s pulse can heat the FTO substrate to 480 &#176;C, while the perovskite remains at ~70 &#176;C, promoting vertical evaporation of the solvent and lateral growth of crystals across the substrate. Heat is quickly dissipated via cooling from the external case, and within seconds, room temperature is reached.
The nucleation and crystallization processes, and thus the final morphology of the film, can be varied through FIRA parameters such as pulse length, frequency, and intensity, allowing for a much more reproducible and controllable crystal growth16. Assuming time-limited nucleation, the pulse length determines the nucleation density whereas the pulse intensity determines the energy provided for crystallization. Insufficient energy would result in incomplete solvent evaporation or crystallization, whereas excess energy would result in thermal degradation of the perovskite15. Optimization of these factors is, therefore, important for the formation of a homogeneous perovskite film, which can affect the optoelectronic properties of the final device.
Compared to the AS method, FIRA has a slower nucleation and faster crystal growth, leading to larger crystalline domains (~40 &#181;m for FIRA vs ~200 nm for AS)16. The lower nucleation rate could be due to a lower supersaturation or a limited nucleation phase as controlled by the duration of the pulse15. However, the difference in grain size does not affect charge carrier mobility and lifetime (mobility ~15 cm2/Vs for AS and ~19 cm2/Vs for FIRA)17 and gives films with similar structural and optical properties, as measured by X-ray diffraction (XRD) and photoluminescence (PL)12. In fact, reports suggest that larger grain sizes are favorable due to suppressed perovskite degradation at grain boundaries4. Compact, defect-tolerant, and highly crystalline perovskite films can be formed with both methods, giving devices with &#62;20% PCE18.
Additionally, the elimination of the antisolvent and the reduction in annealing time from hours to seconds make it much more cost-effective and environmentally friendly. With this method, a crystalline mesoscopic-TiO2 layer can also be manufactured, reducing the energy-intensive sintering step (at 450 &#176;C for 30 min, 1&#8211;3 h in total) to just 10 min16,18. TiO2 annealing times as short as seconds have also been previously reported using variations of this method19,20,21,22. As a result, a whole PSC can be fabricated in less than an hour18. This method is also compatible with industrial upscaling and commercialization as it can be adapted to large-area deposition and roll-to-roll processing for fast and synchronized throughput production15. Furthermore, the water-cooling system allows rapid heat dissipation, making it suitable for the fabrication of devices on flexible substrates such as PET.
FIRA can be used for any wet, thin film that can be deposited via a simple solution process and crystallized at different temperatures up to 1,000 &#176;C. The parameters can be optimized such that crystals in the desired morphology are formed. For example, it has been used for the synthesis of various perovskite compositions on glass and PET12,15,18, as well as the mesoscopic-TiO2 layer on glass, giving devices of &#62;20% PCE18. It also allows for the study of phase evolution against temperature, as the oven and substrate surface temperatures are measured to give a temperature profile of the crystallization process16,17.
This paper firstly discusses the protocol used for the optimization of annealing parameters to synthesize a compact, defect-tolerant, and homogeneous perovskite (MAPbI3) film, which simultaneously offers insight into perovskite morphology evolution against temperature/pulse time. Secondly, a protocol for the processing of perovskite solar cells with FIRA-annealed mesoscopic-TiO2 and perovskite layers is discussed. For this study, a perovskite composition based on formamidinium (80%), caesium (15%), and guanidinium (5%) cations was used (herein denoted FCG), and a tetrabutyl ammonium iodide (TBAI) post-treatment was carried out. Therefore, this paper aims to demonstrate the versatility of the FIRA method, its advantages over the conventional antisolvent method, and its potential to be applied in the eventual commercialization of perovskite solar cells20,21,22.
This protocol is divided into 4 sections: 1) A general description of the operation of the FIRA oven 2) Process for the optimization and synthesis of a MAPbI3 perovskite film on FTO glass 3) Processing of FCG perovskite solar cells and 4) Synthesis of MAPbI3 films on ITO-PET.

<table><tbody><tr><td>4-tert-butylpyridine</td><td>Sigma Aldrich</td><td>142379</td><td></td></tr><tr><td>Acetonitrile, anhydrous</td><td>ACROS Organics</td><td>AC610220010</td><td></td></tr><tr><td>Acetylacetone</td><td>Sigma Aldrich</td><td>P7754</td><td></td></tr><tr><td>Caesium iodide</td><td>Sigma Aldrich</td><td>203033</td><td></td></tr><tr><td>Chlorobenzene, anhydrous</td><td>ACROS Organics</td><td>AC396971000</td><td></td></tr><tr><td>Digital source meter</td><td>Metrohm</td><td>PGSTAT302N Autolab</td><td></td></tr><tr><td>DMF, anhydrous</td><td>ACROS Organics</td><td>AC326871000</td><td></td></tr><tr><td>DMSO, anhydrous</td><td>ACROS Organics</td><td>AC326881000</td><td></td></tr><tr><td>Ethanol</td><td>Sigma Aldrich</td><td>459844</td><td></td></tr><tr><td>FIRA Software</td><td>Labview</td><td></td><td>Developed in-house</td></tr><tr><td>FK209</td><td>Dyenamo</td><td>DN-P04</td><td></td></tr><tr><td>Formamidinium iodide</td><td>GreatCell Solar</td><td>SKU MS150000</td><td></td></tr><tr><td>FTO glass</td><td>Nippon Sheet Glass</td><td>NSG 10</td><td>Sheet resistance = 11-13 ohms/sq</td></tr><tr><td>Guanidinium iodide</td><td>Sigma Aldrich</td><td>806056</td><td></td></tr><tr><td>Cleaning Soap</td><td>Hellmanex III</td><td>-</td><td></td></tr><tr><td>Hydrochloric acid</td><td>Sigma Aldrich</td><td>320331</td><td></td></tr><tr><td>Isopropanol</td><td>Sigma Aldrich</td><td>190764</td><td></td></tr><tr><td>ITO PET</td><td>Sigma Aldrich</td><td>639303</td><td>Sheet resistance = 60 ohms/sq</td></tr><tr><td>Lead iodide</td><td>TCI</td><td>L0279</td><td></td></tr><tr><td>Li-TFSI</td><td>Sigma Aldrich</td><td>544094</td><td></td></tr><tr><td>Mesoporous TiO2 paste, 3 nrd</td><td>GreatCell Solar</td><td>SKU MS002300</td><td></td></tr><tr><td>Methylammonium iodide</td><td>GreatCell Solar</td><td>SKU MS1010000</td><td></td></tr><tr><td>Microscope</td><td>Zeiss</td><td>Axio-Scope A1 Polarizing Microscope</td><td></td></tr><tr><td>Microscope lens</td><td>Zeiss</td><td>EC Epiplan-Apochromat</td><td></td></tr><tr><td>Microscope xenon light source</td><td>Ocean Optics</td><td>HPX-2000</td><td></td></tr><tr><td>Optical fibre</td><td>Ocean Optics</td><td>QP230-2-XSR</td><td>230 &amp;mu;m core</td></tr><tr><td>Plasma cleaner</td><td>Jetlight Company Inc.</td><td>UVO-Cleaner Model no. 256-220</td><td></td></tr><tr><td>Polymer-planarised paper</td><td>Arjowiggins</td><td>Powercoat HD</td><td></td></tr><tr><td>Scanning electron microscope</td><td>Zeiss</td><td>Merlin Microscope</td><td></td></tr><tr><td>Sintering hot plate</td><td>Harry Gestigkeit GMBH</td><td>-</td><td></td></tr><tr><td>Solar simulator</td><td>ABET Technologies</td><td>Model 11016 Sun 2000</td><td></td></tr><tr><td>Spectrometer</td><td>Ocean Optics</td><td>Maya2000 Pro</td><td>Spectral range: 300-1100 nm</td></tr><tr><td>Spiro-OMeTAD</td><td>Sigma Aldrich</td><td>792071</td><td></td></tr><tr><td>Tetrabutyl ammonium iodide</td><td>GreatCell Solar</td><td>SKU MS106000</td><td></td></tr><tr><td>Thermal evaporator</td><td>Kurt J. Lesker</td><td>-</td><td></td></tr><tr><td>titanium diisopropoxide bis(acetylacetonate)</td><td>Sigma Aldrich</td><td>325252</td><td></td></tr><tr><td>X-ray diffractometer</td><td>PANanalytical</td><td>Empyrean diffractometer (theta-theta, 240 mm)</td><td>equipped with a PIXcel-1D detector, Bragg-Brentano beam optics and parallel beam optics</td></tr><tr><td>Zinc powder</td><td>Sigma Aldrich</td><td>324930</td><td></td></tr></tbody></table>

flash infrared annealing for perovskite solar cell processing

Organic&#8211;inorganic perovskites have an impressive potential for the design of next generation solar cells and are currently considered for upscaling and commercialization. Currently, perovskite solar cells rely on spin-coating which is neither practical for large areas nor environmentally friendly. Indeed, one of the conventional and most effective lab-scale methods to induce perovskite crystallization, the antisolvent method, requires an amount of toxic solvent that is difficult to apply on larger surfaces. To solve this problem, an antisolvent-free and rapid thermal annealing process called flash infrared annealing (FIRA) can be used to produce highly crystalline perovskite films. The FIRA oven is composed of an array of near-infrared halogen lamps with an illumination power of 3,000 kW/m2. A hollow aluminum body enables an effective water-cooling system. The FIRA method allows the synthesis of perovskite films in less than 2 s, achieving efficiencies &#62;20%. FIRA has a unique potential for the industry because it can be adapted to continuous processing, is antisolvent-free, and does not require lengthy, hour-long annealing steps.

Optimization and synthesis of MAPbI3 films on FTO glass 
To assess perovskite film quality, microscope images, X-ray diffraction, and absorbance spectra were taken. The optimum pulse time should yield a compact, uniform, and pinhole-free film with large crystal grains. Figure 3 shows optical images of MAPbI3 films at pulse times ranging from 0 s to 7 s, while Figure 4 shows the XRD spectra of films annealed at selective pulse times. These pulse times represent the boundaries of the four distinct perovskite phases observed based on the various characterizations carried out. The phase evolution as a function of pulse time and temperature is shown in Figure 5, and a comparison of the top-view SEM images of films formed by both FIRA and antisolvent methods are found in supplementary information S1. XRD patterns for all pulses and corresponding absorbance spectra are found in supplementary information S2 and S3. Pulses from 0 to 1.6 s gave needle-like crystals or small crystalline domains separated by non-crystalline phases, as evidenced by the precursor peaks at 2&#952; = 6.59, 7.22, and 9.22&#176;29. For 1.8 to 3.8 s pulses, well-defined crystal grains were formed, and XRD patterns showed the formation of the MAPbI3 tetragonal I4/mcm phase. This is also confirmed by the absorption onset of 780 nm. However, longer pulse times led to thermal degradation of the perovskite, with complete degradation for pulses &#62;5 s, as shown by the evolution of the PbI2 peak at 2&#952; = 12.7&#176;. The optimized pulse was determined to be 2 s, giving crystal grains of ~30 &#181;m. Therefore, FIRA allows for a comprehensive study of the nucleation and crystallization processes based on temperature, as controlled by the pulse time. The parameters can also be varied and optimized for different thin films, showing the versatility of this method.
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61730/61730fig03.jpg" /> 
Figure 3: Optical images of MAPbI3 perovskite films on FTO glass, annealed with pulses ranging from 0 s to 7 s.&#160;All images were taken at 10x magnification in transmission mode. <a href="https://www.jove.com/files/ftp_upload/61730/61730fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61730/61730fig04.jpg" /> 
Figure 4: XRD spectra of MAPbI3 films annealed at selective pulse times.&#160;Labeled planes are representative of the tetragonal I4/mcm phase. Asterisked peaks represent diffractions from PbI2, while the blue rectangle represents those from the precursor solution. <a href="https://www.jove.com/files/ftp_upload/61730/61730fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/61730/61730fig05.jpg" /> 
Figure 5: Temperature profile showing perovskite phase evolution as a function of pulse length.&#160;The boundary of the different phases has been determined from the corresponding XRD analysis, shown in Figure 4. Adapted from15. <a href="https://www.jove.com/files/ftp_upload/61730/61730fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
FCG perovskite devices 
Figure 6A,B show the temperature profile and XRD pattern of the mesoscopic-TiO2 layer annealed with a FIRA cycle of 10 pulses, 15 s on and 45 s off. With FIRA, temperatures of ~600 &#176;C could be reached and the TiO2 layer can be synthesized in just 10 min, much shorter than the conventional method which requires sintering for 1 h to 3 h, peaking at 450 &#176;C. The resulting film shows no discernible difference to that sintered on a hot plate. As a result, the whole perovskite solar cell could be processed in less than an hour. The cross-sectional SEM image (Figure 6C) shows that the subsequent devices fabricated are very similar to those made via traditional methods, with layers of similar thickness and morphology. Additionally, FIRA-processed devices showed excellent performance (Figure 7), with the champion device showing PCE = 20.1%, FF = 75%, Voc = 1.1 V, and Jsc = 24.4 mA/cm2, comparable to devices fabricated with the antisolvent method. A large-area device with a 1.4 cm2 active area also gave PCE of 17%, showing FIRA is a promising alternative processing method for the manufacture of PSCs.
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/61730/61730fig06.jpg" /> 
Figure 6: (A) Temperature profile of mesoporous TiO2 annealing in FIRA, with a cycle of 10 pulses of 15 s on and 45 s off. (B) X-ray patterns for TiO2 films annealed with a hotplate and FIRA, and a blank FTO substrate as reference. (C) Cross-sectional SEM images of perovskite solar cell architectures, processed by FIRA and antisolvent. Reproduced with permission from18. <a href="https://www.jove.com/files/ftp_upload/61730/61730fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/61730/61730fig07.jpg" /> 
Figure 7: Current-voltage curve for champion FCG perovskite devices.&#160;(A) FIRA-annealed mesoporous-TiO2 and perovskite layers. (B) Large area (1.4 cm2) device with FIRA-annealed mesoporous-TiO2 and perovskite layers. Reproduced with permission from18. <a href="https://www.jove.com/files/ftp_upload/61730/61730fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
MAPbI3 films on ITO-PET
Figure 8 shows optical images of MAPbI3 films annealed at pulses ranging from 1 s to 2 s. At shorter pulse times, there is incomplete crystallization, whereas at pulse times &#62;1.7 s, the PET substrate begins to melt (see Supplemental Figure 4). Thermal degradation of the perovskite is also observed for the 2 s pulse. At the optimized pulse time of 1.7 s, densely packed crystal domains of ~15 &#181;m were observed. Although there are small pinholes of 1&#8211;2 &#181;m, it is clear that FIRA can be used to form compact and uniform perovskite films on flexible polymers without melting the substrate, due to rapid cooling from the case, which is a significant advantage compared to hotplate annealing.
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/61730/61730fig08.jpg" /> 
Figure 8: Optical images of MAPbI3 films annealed at various pulse times on ITO-PET.&#160;All images are taken in transmission mode and 10x magnification unless otherwise specified. <a href="https://www.jove.com/files/ftp_upload/61730/61730fig08large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Supplemental Figure 1: Top-view SEM comparison of FIRA and hotplate annealed perovskite films. (A) Top view of FIRA-annealed perovskite films for four annealing times, scale bar: 25 &#181;m. (B) Top view of a reference film made by the antisolvent method followed by annealing at 100 &#176;C for 1 h on a standard hotplate, scale bar: 1 &#181;m. Adapted from1. <a href="https://cloudflare.jove.com/files/ftp_upload/61730/61730supfig01.jpg" target="_blank">Please click here to download this figure.</a>
Supplemental Figure 2: XRD spectra of MAPbI3 films on FTO glass, annealed with pulses of (A) 0&#8211;1.4 s (B) 1.6&#8211;3 s (C) 3.2&#8211;4.6 s (D) 4.8&#8211;7 s. <a href="https://cloudflare.jove.com/files/ftp_upload/61730/61730supfig02.jpg" target="_blank">Please click here to download this figure.</a>
Supplemental Figure 3: Absorbance spectra of MAPbI3 films on FTO glass, annealed with pulses of (A) 0.2&#8211;1.8 s (B) 2&#8211;3.6 s (C) 3.8&#8211;7 s. <a href="https://cloudflare.jove.com/files/ftp_upload/61730/61730supfig03.jpg" target="_blank">Please click here to download this figure.</a>
Supplemental Figure 4: Physical appearance of MAPbI3 films annealed on PET at various pulse lengths. <a href="https://cloudflare.jove.com/files/ftp_upload/61730/61730supfig04.jpg" target="_blank">Please click here to download this figure.</a>
Supplemental Figure 5: Temperature profile and top-view SEM images of the pristine paper substrate, ITO electrode, and mesoporous-TiO2 layer processed with FIRA. <a href="https://cloudflare.jove.com/files/ftp_upload/61730/61730supfig05.jpg" target="_blank">Please click here to download this figure.</a>
Supplemental Figure 6: Cross-sectional SEM image of perovskite deposited (via antisolvent method) on a FIRA-annealed ITO/TiO2 stack on a paper substrate. ITO np = ITO nanoparticles, pvk = perovskite. <a href="https://cloudflare.jove.com/files/ftp_upload/61730/61730supfig06.jpg" target="_blank">Please click here to download this figure.</a>

Watch this Scientific Journal Video about Flash Infrared Annealing for Perovskite Solar Cell Processing at JoVE.com

Flash Infrared Annealing for Perovskite Solar Cell Processing

We describe a flash infrared annealing method used for the synthesis of perovskite and mesoscopic-TiO2 films. Annealing parameters are varied and optimized for processing on fluorine-doped tin oxide (FTO) glass and indium tin oxide-coated polyethylene terephthalate (ITO PET), subsequently giving devices power conversion efficiencies &#62;20%.

Organic&#8211;inorganic perovskites have an impressive potential for the design of next generation solar cells and are currently considered for upscaling ...

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Research

JoVE Journal

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7.8K Views.  Imperial College London. We describe a flash infrared annealing method used for the synthesis of perovskite and mesoscopic-TiO2 films. Annealing parameters are varied and optimized for processing on fluorine-doped tin oxide (FTO) glass and indium tin oxide-coated polyethylene terephthalate (ITO PET), subsequently giving devices power conversion efficiencies >20%.

Video: Flash Infrared Annealing for Perovskite Solar Cell Processing

Polycrystalline Silicon Thin-film Solar cells with Plasmonic-enhanced Light-trapping

One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To compensate for lower light absorption such physically thin devices have to incorporate light-trapping which increases their optical thickness. Light scattering by textured surfaces is a common technique but it cannot be universally applied to all solar cell technologies. Some cells, for example those made of evaporated silicon, are planar as produced and they require an alternative light-trapping means suitable for planar devices. Metal nanoparticles formed on planar silicon cell surface and capable of light scattering due to surface plasmon resonance is an effective approach.
The paper presents a fabrication procedure of evaporated polycrystalline silicon solar cells with plasmonic light-trapping and demonstrates how the cell quantum efficiency improves due to presence of metal nanoparticles.
To fabricate the cells a film consisting of alternative boron and phosphorous doped silicon layers is deposited on glass substrate by electron beam evaporation. An Initially amorphous film is crystallised and electronic defects are mitigated by annealing and hydrogen passivation. Metal grid contacts are applied to the layers of opposite polarity to extract electricity generated by the cell. Typically, such a ~2 &mu;m thick cell has a short-circuit current density (Jsc) of 14-16 mA/cm2, which can be increased up to 17-18 mA/cm2 (~25% higher) after application of a simple diffuse back reflector made of a white paint.
To implement plasmonic light-trapping a silver nanoparticle array is formed on the metallised cell silicon surface. A precursor silver film is deposited on the cell by thermal evaporation and annealed at 23&deg;C to form silver nanoparticles. Nanoparticle size and coverage, which affect plasmonic light-scattering, can be tuned for enhanced cell performance by varying the precursor film thickness and its annealing conditions. An optimised nanoparticle array alone results in cell Jsc enhancement of about 28%, similar to the effect of the diffuse reflector. The photocurrent can be further increased by coating the nanoparticles by a low refractive index dielectric, like MgF2, and applying the diffused reflector. The complete plasmonic cell structure comprises the polycrystalline silicon film, a silver nanoparticle array, a layer of MgF2, and a diffuse reflector. The Jsc for such cell is 21-23 mA/cm2, up to 45% higher than Jsc of the original cell without light-trapping or ~25% higher than Jsc for the cell with the diffuse reflector only.
Introduction
Light-trapping in silicon solar cells is commonly achieved via light scattering at textured interfaces. Scattered light travels through a cell at oblique angles for a longer distance and when such angles exceed the critical angle at the cell interfaces the light is permanently trapped in the cell by total internal reflection (Animation 1: Light-trapping). Although this scheme works well for most solar cells, there are developing technologies where ultra-thin Si layers are produced planar (e.g. layer-transfer technologies and epitaxial c-Si layers) 1 and or when such layers are not compatible with textures substrates (e.g. evaporated silicon) 2. For such originally planar Si layer alternative light trapping approaches, such as diffuse white paint reflector 3, silicon plasma texturing 4 or high refractive index nanoparticle reflector 5 have been suggested.
Metal nanoparticles can effectively scatter incident light into a higher refractive index material, like silicon, due to the surface plasmon resonance effect 6. They also can be easily formed on the planar silicon cell surface thus offering a light-trapping approach alternative to texturing. For a nanoparticle located at the air-silicon interface the scattered light fraction coupled into silicon exceeds 95% and a large faction of that light is scattered at angles above critical providing nearly ideal light-trapping condition (Animation 2: Plasmons on NP). The resonance can be tuned to the wavelength region, which is most important for a particular cell material and design, by varying the nanoparticle average size, surface coverage and local dielectric environment 6,7. Theoretical design principles of plasmonic nanoparticle solar cells have been suggested 8. In practice, Ag nanoparticle array is an ideal light-trapping partner for poly-Si thin-film solar cells because most of these design principle are naturally met. The simplest way of forming nanoparticles by thermal annealing of a thin precursor Ag film results in a random array with a relatively wide size and shape distribution, which is particularly suitable for light-trapping because such an array has a wide resonance peak, covering the wavelength range of 700-900 nm, important for poly-Si solar cell performance. The nanoparticle array can only be located on the rear poly-Si cell surface thus avoiding destructive interference between incident and scattered light which occurs for front-located nanoparticles 9. Moreover, poly-Si thin-film cells do not requires a passivating layer and the flat base-shaped nanoparticles (that naturally result from thermal annealing of a metal film) can be directly placed on silicon further increases plasmonic scattering efficiency due to surface plasmon-polariton resonance 10.
The cell with the plasmonic nanoparticle array as described above can have a photocurrent about 28% higher than the original cell. However, the array still transmits a significant amount of light which escapes through the rear of the cell and does not contribute into the current. This loss can be mitigated by adding a rear reflector to allow catching transmitted light and re-directing it back to the cell. Providing sufficient distance between the reflector and the nanoparticles (a few hundred nanometers) the reflected light will then experience one more plasmonic scattering event while passing through the nanoparticle array on re-entering the cell and the reflector itself can be made diffuse - both effects further facilitating light scattering and hence light-trapping. Importantly, the Ag nanoparticles have to be encapsulated with an inert and low refractive index dielectric, like MgF2 or SiO2, from the rear reflector to avoid mechanical and chemical damage 7. Low refractive index for this cladding layer is required to maintain a high coupling fraction into silicon and larger scattering angles, which are ensured by the high optical contrast between the media on both sides of the nanoparticle, silicon and dielectric 6. The photocurrent of the plasmonic cell with the diffuse rear reflector can be up to 45% higher than the current of the original cell or up to 25% higher than the current of an equivalent cell with the diffuse reflector only.

Polycrystalline silicon thin-film solar cells on glass are fabricated by deposition of boron and phosphorous doped silicon layers followed by crystallisation, defect passivation and metallisation. Plasmonic light-trapping is introduced by forming Ag nanoparticles on the silicon cell surface capped with a diffused reflector resulting in ~45% photocurrent enhancement.

One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To ...

Engineering

Using Neutron Spin Echo Resolved Grazing Incidence Scattering to Investigate Organic Solar Cell Materials

The spin echo resolved grazing incidence scattering (SERGIS) technique has been used to probe the length-scales associated with irregularly shaped crystallites. Neutrons are passed through two well defined regions of magnetic field; one before and one after the sample. The two magnetic field regions have opposite polarity and are tuned such that neutrons travelling through both regions, without being perturbed, will undergo the same number of precessions in opposing directions. In this case the neutron precession in the second arm is said to &#34;echo&#34; the first, and the original polarization of the beam is preserved. If the neutron interacts with a sample and scatters elastically the path through the second arm is not the same as the first and the original polarization is not recovered. Depolarization of the neutron beam is a highly sensitive probe at very small angles (&#60;50&#160;&#956;rad) but still allows a high intensity, divergent beam to be used. The decrease in polarization of the beam reflected from the sample as compared to that from the reference sample can be directly related to structure within the sample.
In comparison to scattering observed in neutron reflection measurements the SERGIS signals are often weak and are unlikely to be observed if the in-plane structures within the sample under investigation are dilute, disordered, small in size and polydisperse or the neutron scattering contrast is low. Therefore, good results will most likely be obtained using the SERGIS technique if the sample being measured consist of thin films on a flat substrate and contain scattering features that contains a high density of moderately sized features (30 nm to 5 &#181;m) which scatter neutrons strongly or the features are arranged on a lattice. An advantage of the SERGIS technique is that it can probe structures in the plane of the sample.

Progress has been made in utilizing spin echo resolved grazing incidence scattering (SERGIS) as a neutron scattering technique to probe the length-scales in irregular samples. Crystallites of [6,6]-phenyl-C61-butyric acid methyl ester have been probed using the SERGIS technique and the results confirmed by optical and atomic force microscopy.

The spin echo resolved grazing incidence scattering (SERGIS) technique has been used to probe the length-scales associated with irregularly shaped ...

Integrating a Triplet-triplet Annihilation Up-conversion System to Enhance Dye-sensitized Solar Cell Response to Sub-bandgap Light

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents and hence higher efficiencies. Photon up-conversion by way of triplet-triplet annihilation (TTA-UC) is an attractive technique for using these otherwise wasted low energy photons to produce photocurrent, while not interfering with the photoanodic performance in a deleterious manner. Further to this, TTA-UC has a number of features, distinct from other reported photon up-conversion technologies, which renders it particularly suitable for coupling with DSC technology. In this work, a proven high performance TTA-UC system, comprising a palladium porphyrin sensitizer and rubrene emitter, is combined with a high performance DSC (utilizing the organic dye D149) in an integrated device. The device shows an enhanced response to sub-bandgap light over the absorption range of the TTA-UC sub-unit resulting in the highest figure of merit for up-conversion assisted DSC performance to date.

An integrated device, incorporating a dye-sensitized solar cell and triplet-triplet annihilation up-conversion unit was produced, affording enhanced light harvesting, from a wider section of the solar spectrum. Under modest irradiation levels a significantly enhanced response to low energy photons was demonstrated, yielding a record figure of merit for dye-sensitized solar cells.

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents ...

Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 &#176;C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl- anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136&#177;39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.

This protocol describes the synthesis and solution deposition of inorganic nanocrystals layer by layer to produce thin film electronics on non-conductive surfaces. Solvent-stabilized inks can produce complete photovoltaic devices on glass substrates via spin and spray coating following post-deposition ligand exchange and sintering.

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal ...

Influence of Hybrid Perovskite Fabrication Methods on Film Formation, Electronic Structure, and Solar Cell Performance

Hybrid organic/inorganic halide perovskites have lately been a topic of great interest in the field of solar cell applications, with the potential to achieve device efficiencies exceeding other thin film device technologies. Yet, large variations in device efficiency and basic physical properties are reported. This is due to unintentional variations during film processing, which have not been sufficiently investigated so far. We therefore conducted an extensive study of the morphology and electronic structure of a large number of CH3NH3PbI3 perovskite where we show how the preparation method as well as the mixing ratio of educts methylammonium iodide and lead(II) iodide impact properties like film formation, crystal structure, density of states, energy levels, and ultimately the solar cell performance.

We present an extensive study on the effects of different fabrication methods for organic/inorganic perovskite thin films by comparing crystal structures, density of states, energy levels, and ultimately the solar cell performance.

Hybrid organic/inorganic halide perovskites have lately been a topic of great interest in the field of solar cell applications, with the potential to ...

Chemistry

Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films

Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, we present a protocol for the fabrication of this material via the low-pressure vapor assisted solution process (LP-VASP) method, which yields ~19% power conversion efficiency in planar heterojunction perovskite solar cells. First, we report the synthesis of methylammonium iodide (CH3NH3I) and methylammonium bromide (CH3NH3Br) from methylamine and the corresponding halide acid (HI or HBr). Then, we describe the fabrication of pinhole-free, continuous methylammonium-lead halide perovskite (CH3NH3PbX3 with X = I, Br, Cl and their mixture) films with the LP-VASP. This process is based on two steps: i) spin-coating of a homogenous layer of lead halide precursor onto a substrate, and ii) conversion of this layer to CH3NH3PbI3-xBrx by exposing the substrate to vapors of a mixture of CH3NH3I and CH3NH3Br at reduced pressure and 120 &#176;C. Through slow diffusion of the methylammonium halide vapor into the lead halide precursor, we achieve slow and controlled growth of a continuous, pinhole-free perovskite film. The LP-VASP allows synthetic access to the full halide composition space in CH3NH3PbI3-xBrx with 0&#160;&#8804; x&#160;&#8804; 3. Depending on the composition of the vapor phase, the bandgap can be tuned between 1.6 eV&#160;&#8804; Eg&#160;&#8804; 2.3 eV. In addition, by varying the composition of the halide precursor and of the vapor phase, we can also obtain CH3NH3PbI3-xClx. Films obtained from the LP-VASP are reproducible, phase pure as confirmed by X-ray diffraction measurements, and show high photoluminescence quantum yield. The process does not require the use of a glovebox.

Here, we present a protocol for the synthesis of CH3NH3I and CH3NH3Br precursors and the subsequent formation of pinhole-free, continuous CH3NH3PbI3-xBrx thin films for the application in high efficiency solar cells and other optoelectronic devices.

Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, ...

Morphology Control for Fully Printable Organic&#8211;Inorganic Bulk-heterojunction Solar Cells Based on a Ti-alkoxide and Semiconducting Polymer

The photoactive layer of a typical organic thin-film bulk-heterojunction (BHJ) solar cell commonly uses fullerene derivatives as the electron-accepting material. However, fullerene derivatives are air-sensitive; therefore, air-stable material is needed as an alternative. In the present study, we propose and describe the properties of Ti-alkoxide as an alternative electron-accepting material to fullerene derivatives to create highly air-stable BHJ solar cells. It is well-known that controlling the morphology in the photoactive layer, which is constructed with fullerene derivatives as the electron acceptor, is important for obtaining a high overall efficiency through the solvent method. The conventional solvent method is useful for high-solubility materials, such as fullerene derivatives. However, for Ti-alkoxides, the conventional solvent method is insufficient, because they only dissolve in specific solvents. Here, we demonstrate a new approach to morphology control that uses the molecular bulkiness of Ti-alkoxides without the conventional solvent method. That is, this method is one approach to obtain highly efficient, air-stable, organic-inorganic bulk-heterojunction solar cells.

A method for fully printable, fullerene-free, highly air-stable, bulk-heterojunction solar cells based on Ti alkoxides as the electron acceptor and the electron-donating polymer fabrication is described here. Moreover, a method for controlling the morphology of the photoactive layer through the molecular bulkiness of the Ti-alkoxide units is reported.

The photoactive layer of a typical organic thin-film bulk-heterojunction (BHJ) solar cell commonly uses fullerene derivatives as the electron-accepting ...

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials such as organo-lead halide perovskites is presented. The perovskite film thickness and absorption coefficient are initially characterized by profilometry and UV-VIS absorption spectroscopy. Calibration of both laser power and cavity sensitivity is described in detail. A protocol for performing Flash-photolysis Time Resolved Microwave Conductivity (TRMC) experiments, a non-contact method of determining the conductivity of a material, is presented. A process for identifying the real and imaginary components of the complex conductivity by performing TRMC as a function of microwave frequency is given. Charge carrier dynamics are determined under different excitation regimes (including both power and wavelength). Techniques for distinguishing between direct and trap-mediated decay processes are presented and discussed. Results are modelled and interpreted with reference to a general kinetic model of photoinduced charge carriers in a semiconductor. The techniques described are applicable to a wide range of optoelectronic materials, including organic and inorganic photovoltaic materials, nanoparticles, and conducting/semiconducting thin films.

A Time Resolved Microwave Conductivity technique for investigating direct and trap-mediated recombination dynamics and determining carrier mobilities of thin film semiconductors is presented here.

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials ...

Monovalent Cation Doping of CH3NH3PbI3 for Efficient Perovskite Solar Cells

Here, we demonstrate the incorporation of monovalent cation additives into CH3NH3PbI3 perovskite in order to adjust the optical, excitonic, and electrical properties. The possibility of doping was investigated by adding monovalent cation halides with similar ionic radii to Pb2+, including Cu+, Na+, and Ag+. A shift in the Fermi level and a remarkable decrease of sub-bandgap optical absorption, along with a lower energetic disorder in the perovskite, was achieved. An order-of-magnitude enhancement in the bulk hole mobility and a significant reduction of transport activation energy within an additive-based perovskite device was attained. The confluence of the aforementioned improved properties in the presence of these cations led to an enhancement in the photovoltaic parameters of the perovskite solar cell. An increase of 70 mV in open circuit voltage for AgI and a 2 mA/cm2 improvement in photocurrent density for NaI- and CuBr-based solar cells were achieved compared to the pristine device. Our work paves the way for further improvements in the optoelectronic quality of CH3NH3PbI3 perovskite and subsequent devices. It highlights a new avenue for investigations on the role of dopant impurities in crystallization and controls the electronic defect density in perovskite structures.

Monovalent Cation Doping of CH3NH3PbI3 for Efficient Perovskite Solar Cells

Here, we present a protocol to adjust the properties of solution-processed CH3NH3PbI3 through the incorporation of monovalent cation additives in order to achieve highly efficient perovskite solar cells.

Here, we demonstrate the incorporation of monovalent cation additives into CH3NH3PbI3 perovskite in order to adjust the optical, excitonic, and electrical ...

In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. Currently, the surface temperature of objects processed in conveyor belt furnaces is typically measured via thermocouples. However, infrared (IR) thermography presents multiple advantages compared to thermocouple measurements, as it is a contactless, real-time, and spatially resolved method. Here, as a representative proof-of-concept example, an inline thermography system is successfully installed into an IR lamp powered solar firing furnace, which is used for the contact firing process of industrial Si solar cells. This protocol describes how to install an IR camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and perform the evaluation of spatial surface temperature distribution on a target object.

This protocol describes how to install an infrared camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and evaluate the spatial surface temperature distribution of an object of interest. The example objects are industrial silicon solar cells.

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. ...

Flash Infrared Annealing for Perovskite Solar Cell Processing

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