Name: recombination dynamics in thin-film photovoltaic materials via time-resolved microwave conductivity
Uploaded: 2017-03-06T13:00:00
Description: Watch this Scientific Journal Video about Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity at JoVE.com

Acknowledgment is made to the Australian Research Council (LE130100146, DP160103008). JAG is supported via an Australian Postgraduate Award, and DRM by an ARC Future Fellowship (FT130100214). We thank Nikos Kopidakis for helpful discussions.

1. Sample Preparation
Caution: Some chemicals used in this protocol can be hazardous to health. Please consult all relevant material safety data sheets before any sample preparation takes place. Utilize appropriate personal protective equipment (lab coats, safety glasses, gloves, etc.) and engineering controls (e.g. glovebox, fume hood, etc.) when handling the perovskite precursors, and solvents.
NOTE: The aim of this section is to form a un...

<ol>
	<li>Park, J., Reid, O. G., Blackburn, J. L., Rumbles, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photoinduced+spontaneous+free-carrier+generation+in+semiconducting+single-walled+carbon+nanotubes.">Photoinduced spontaneous free-carrier generation in semiconducting single-walled carbon nanotubes.</a> Nat. Comm. 6 (8809), (2015).</li><li>Dicker, G., de Haas, M. P., Siebbeles, L. D., Warman, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrodeless+time-resolved+microwave+conductivity+study+of+charge-carrier+photogeneration+in+regioregular+poly+(3-hexylthiophene)+thin+films.">Electrodeless time-resolved microwave conductivity study of charge-carrier photogeneration in regioregular poly (3-hexylthiophene) thin films.</a> Phys. Rev. B. 70 (4), 045203 (2004).</li><li>Oga, H., Saeki, A., Ogomi, Y., Hayase, S., Seki, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+understanding+of+the+electronic+and+energetic+landscapes+of+perovskite+solar+cells:+high+local+charge+carrier+mobility,+reduced+recombination,+and+extremely+shallow+traps.">Improved understanding of the electronic and energetic landscapes of perovskite solar cells: high local charge carrier mobility, reduced recombination, and extremely shallow traps.</a> J. Am. Chem. Soc. 136 (39), 13818-13825 (2014).</li><li>Ponseca, C. 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=Organometal+halide+perovskite+solar+cell+materials+rationalized:+ultrafast+charge+generation,+high+and+microsecond-long+balanced+mobilities,+and+slow+recombination.">Organometal halide perovskite solar cell materials rationalized: ultrafast charge generation, high and microsecond-long balanced mobilities, and slow recombination.</a> J. Am. Chem. Soc. 136 (14), 5189-5192 (2014).</li><li>Guse, J. A., 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=Spectral+dependence+of+direct+and+trap-mediated+recombination+processes+in+lead+halide+perovskites+using+time+resolved+microwave+conductivity.">Spectral dependence of direct and trap-mediated recombination processes in lead halide perovskites using time resolved microwave conductivity.</a> Phys. Chem. Chem. Phys. 18, 12043-12049 (2016).</li><li>Kunst, M., Abdallah, O., W&#252;nsch, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Passivation+of+silicon+by+silicon+nitride+films.">Passivation of silicon by silicon nitride films.</a> Solar energy materials and solar cells. 72 (1-4), 335-341 (2002).</li><li>Hutter, E. M., Eperon, G. E., Stranks, S. D., Savenije, T. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Charge+Carriers+in+Planar+and+Meso-Structured+Organic-Inorganic+Perovskites:+Mobilities,+Lifetimes+and+Concentrations+of+Trap+States.">Charge Carriers in Planar and Meso-Structured Organic-Inorganic Perovskites: Mobilities, Lifetimes and Concentrations of Trap States.</a> J. Phys. Chem. Lett. 6 (15), 3082-3090 (2015).</li><li>Cosme, I., 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=Lifetime+assessment+in+crystalline+silicon:+From+nanopatterned+wafer+to+ultra-thin+crystalline+films+for+solar+cells.">Lifetime assessment in crystalline silicon: From nanopatterned wafer to ultra-thin crystalline films for solar cells.</a> Solar Energy Materials and Solar Cells. 135, 93-98 (2015).</li><li>Katoh, R., Furube, A., Yamanaka, K. I., Morikawa, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Charge+separation+and+trapping+in+N-doped+TiO2+photocatalysts:+A+time-resolved+microwave+conductivity+study.">Charge separation and trapping in N-doped TiO2 photocatalysts: A time-resolved microwave conductivity study.</a> J. Phys. Chem. Lett. 1 (22), 3261-3265 (2010).</li><li>Colbeau-Justin, C., Valenzuela, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time-resolved+microwave+conductivity+(TRMC)+a+useful+characterization+tool+for+charge+carrier+transfer+in+photocatalysis:+a+short+review.">Time-resolved microwave conductivity (TRMC) a useful characterization tool for charge carrier transfer in photocatalysis: a short review.</a> Revista mexicana de f&#237;sica. 59 (3), 191-200 (2013).</li><li>Luna, A. L., 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=Synergetic+effect+of+Ni+and+Au+nanoparticles+synthesized+on+titania+particles+for+efficient+photocatalytic+hydrogen+production.">Synergetic effect of Ni and Au nanoparticles synthesized on titania particles for efficient photocatalytic hydrogen production.</a> Applied Catalysis B: Environmental. 191, 18-28 (2016).</li><li>Ferguson, A. J., Kopidakis, N., Shaheen, S. E., Rumbles, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quenching+of+excitons+by+holes+in+poly+(3-hexylthiophene)+films.">Quenching of excitons by holes in poly (3-hexylthiophene) films.</a> J. Phys. Chem. C. 112 (26), 9865-9871 (2008).</li><li>Ferguson, A. J., Kopidakis, N., Shaheen, S. E., Rumbles, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dark+carriers,+trapping,+and+activation+control+of+carrier+recombination+in+neat+P3HT+and+P3HT:+PCBM+blends.">Dark carriers, trapping, and activation control of carrier recombination in neat P3HT and P3HT: PCBM blends.</a> J. Phys. Chem. C. 115 (46), 23134-23148 (2011).</li><li>Savenije, T. J., Ferguson, A. J., Kopidakis, N., Rumbles, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Revealing+the+Dynamics+of+Charge+Carriers+in+Polymer:fullerene+Blends+Using+Photoinduced+Time-Resolved+Microwave+Conductivity.">Revealing the Dynamics of Charge Carriers in Polymer:fullerene Blends Using Photoinduced Time-Resolved Microwave Conductivity.</a> J. Phys. Chem. C. 117 (46), 24085-24103 (2013).</li><li>Xiao, Z., 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=Efficient,+high+yield+perovskite+photovoltaic+devices+grown+by+interdiffusion+of+solution-processed+precursor+stacking+layers.">Efficient, high yield perovskite photovoltaic devices grown by interdiffusion of solution-processed precursor stacking layers.</a> Energy Environ. Sci. 7 (8), 2619-2623 (2014).</li><li>Infelta, P. P., De Haas, M. P., Warman, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+study+of+the+transient+conductivity+of+pulse+irradiated+dielectric+liquids+on+a+nanosecond+timescale+using+microwaves.">The study of the transient conductivity of pulse irradiated dielectric liquids on a nanosecond timescale using microwaves.</a> Radiat. Phys. Chem. 10 (5-6), 353-365 (1977).</li><li>Saeki, A., Seki, S., Sunagawa, T., Ushida, K., Tagawa, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Charge-carrier+dynamics+in+polythiophene+films+studied+by+in-situ+measurement+of+flash-photolysis+time-resolved+microwave+conductivity+(FP-TRMC)+and+transient+optical+spectroscopy+(TOS).">Charge-carrier dynamics in polythiophene films studied by in-situ measurement of flash-photolysis time-resolved microwave conductivity (FP-TRMC) and transient optical spectroscopy (TOS).</a> Philosophical Magazine. 86 (9), 1261-1276 (2006).</li><li>Choi, W., Miyakai, T., Sakurai, T., Saeki, A., Yokoyama, M., Seki, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non-contact,+non-destructive,+quantitative+probing+of+interfacial+trap+sites+for+charge+carrier+transport+at+semiconductor-insulator+boundary.">Non-contact, non-destructive, quantitative probing of interfacial trap sites for charge carrier transport at semiconductor-insulator boundary.</a> Appl. Phys. Lett. 105 (3), 033302 (2014).</li></ol>

While the TRMC technique can offer a wealth of information about photoinduced charge carrier dynamics, this is an indirect measurement of conductivity, and therefore care needs to be taken when interpreting results. The TRMC technique measures total mobility, and cannot be used to distinguish between electron and hole mobilities. The underlying assumption that conductivity is proportional to change in reflected power holds only when that change is small (&#60; 5%)16. Furthermore, if the shift in r...

Flash-photolysis time-resolved microwave conductivity (FP-TRMC) monitors dynamics of photo-excited charge carriers on the ns-&#181;s timescale, making it an ideal tool for investigating charge carrier recombination processes. Understanding the decay mechanisms of photo-induced charge carriers in thin film semiconductors is of key importance in a range of applications, including photovoltaic device optimization. The induced carrier lifetimes are often functions of induced carrier density, excitation wavelength, mobility, trap density and trapping rate. This paper demonstrates the versatility of the Time Resolved Microwave Conductivity (TRMC) technique for investigating a wide range of carrier dynamic dependencies (intensity, wavelength, microwave frequency) and their interpretations.
Photogenerated charges can modify to both the real and the imaginary parts of the dielectric constant of a material, depending on their mobility and degree of confinement/localization1. The conductivity of a material <img alt="Equation" src="/files/ftp_upload/55232/55232eq1.jpg" /> is proportional to its complex dielectric constant
<img alt="Equation" src="/files/ftp_upload/55232/55232eq2.jpg" />
where <img alt="Equation" src="/files/ftp_upload/55232/55232eq3.jpg" /> is the frequency of a microwave electric field, <img alt="Equation" src="/files/ftp_upload/55232/55232eq4.jpg" /> and <img alt="Equation" src="/files/ftp_upload/55232/55232eq5.jpg" /> are the real and imaginary parts of the dielectric constant. Thus, the real part of the conductivity is related to the imaginary part of the dielectric constant, and can be mapped onto microwave absorption, while the imaginary part of the conductivity (subsequently referred to as polarization) is related to a shift in the resonance frequency of the microwave field1.
TRMC offers several advantages over other techniques. For instance, DC photoconductivity measurements suffer from a range of complications arising from contacting the material with electrodes. Enhanced recombination at the electrode/material interface, back injection of charges through this interface, as well as enhanced dissociation of excitons and geminate pairs due to the applied voltage2 all lead to distortions in the measured carrier mobilities and lifetimes. In contrast, TRMC is an electrodeless technique which measures the intrinsic mobility of the carriers without distortions due to charge transfer across contacts.
A significant advantage of using microwave power as a probe for carrier dynamics is that, as well as monitoring the decay lifetimes of charge carriers, decay mechanisms/pathways can also be investigated.
TRMC can be used to determine the total mobility3 and lifetime4 of induced charge carriers. These parameters can subsequently be used to distinguish between direct and trap-mediated recombination mechanisms3,5. The dependence of these two separate decay pathways can be quantitatively analyzed as a function of carrier density3,5 and excitation energy/wavelength5. The localization/confinement of induced carriers can be investigated by comparing the decay of the conductivity vs polarizability5 (imaginary vs real part of dielectric constant).
Additionally, and perhaps most importantly, TRMC can be used to characterize trap states which act as charge carrier decay pathways. Surface traps, for example, can be distinguished from bulk traps by comparing passivated vs unpassivated samples6. Sub-bandgap states can be directly investigated using sub-bandgap excitation energies5. Trap densities can be deduced by fitting TRMC data7.
Due to the versatility of this technique, TRMC has been applied to study a wide range of materials including: traditional thin film semiconductors such as silicon6,8 and TiO29,10, nanoparticles11, nanotubes1, organic semiconductors12, material blends13,14, and hybrid photovoltaic materials3,4,5.
In order to obtain quantitative information using TRMC, it is crucial to be able to accurately determine the number of absorbed photons for a given optical excitation. Since methods for quantifying absorption of thin films, nanoparticles, solutions and opaque samples differ, the sample preparation and calibration techniques presented here are designed specifically for thin film samples. However, the TRMC measurement protocol presented is very general.

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			<td>Corrosive and toxic.&#160; See SDS.</td>
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			<td>Lead (II) iodide (99%)</td>
			<td>Sigma Aldrich 
			www.sigmaaldrich.com/catalog/product/aldrich/211168?lang=en&#38;region=AU</td>
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			<td>Anhydrous dimethylformamide (99.8%)</td>
			<td>Sigma Aldrich 
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			<td>Anhydrous dimethylsulfoxide (99.9%)</td>
			<td>Sigma Aldrich 
			www.sigmaaldrich.com/catalog/product/sial/276855?lang=en&#38;region=AU</td>
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			<td>Sigma Aldrich 
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			<td>Methylammonium iodide</td>
			<td>Dyesol 
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			<td>Also sold by Sigma Aldrich</td>
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			<td>Toxic. See SDS</td>
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			<td>&#160;Equipment</td>
			<td>Company</td>
			<td>Model</td>
			<td>Comments/Description</td>
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			<td>UV-VIS-NIR spectrophotometer</td>
			<td>Perkin-Elmer&#160;</td>
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			<td>Keysight 
			www.keysight.com/en/pdx-x201927-pn-N9918A/fieldfox-handheld-microwave-analyzer-265-ghz?cc=US&#38;lc=eng</td>
			<td>Fieldfox N9918A</td>
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			<td>Tunable wavelength laser</td>
			<td>Opotek 
			www.opotek.com/product/opolette-355</td>
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			<td>Thorlabs 
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			<td>NUK01</td>
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			<td>Power meter</td>
			<td>Thorlabs 
			www.thorlabs.com/thorproduct.cfm?partnumber=PM100D</td>
			<td>PM100D</td>
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			<td>Power sensor</td>
			<td>Thorlabs 
			www.thorlabs.com/thorproduct.cfm?partnumber=S401C</td>
			<td>S401C</td>
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		</tr>
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			<td>Cavity</td>
			<td>Custom built</td>
			<td></td>
			<td>The cavity used in for this experiment was designed and built in-house.</td>
		</tr>
	</tbody>
</table>

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.

&#160;The representative results presented here were obtained from a 250 nm CH3NH3PbI3 thin film sample.
The dynamics of the conductivity <img alt="Equation" src="/files/ftp_upload/55232/55232eq54.jpg" /> can be related to the dynamics of the charge carriers <img alt="Equation" src="/files/ftp_upload/55232/55232eq55.jpg" /> via
<img alt...

Watch this Scientific Journal Video about Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity at JoVE.com

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

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 ...

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