This work was supported by the Daegu Gyeongbuk Institute of Science and Technology (DGIST) Research and Development (R&#38;D) Programs of the Ministry of Science, ICT and Future Planning of Korea (18-ET-01).&#160;This work was also supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP) and the Ministry of Trade, Industry &#38; Energy(MOTIE) of the Republic of Korea (No. 20173010013200).

1. Preparation of Bare-glass, Fluorine-doped Tin Oxide (SnO2:F) Substrates
<ol>
	<li>To clean the bare-glass, fluorine-doped tin oxide (FTO) substrates, sonicate them sequentially in an aqueous solution containing 2% Triton, deionized (DI) water, acetone, and isopropyl alcohol (IPA), each for 15 min.</li>
	<li>Put the cleaned substrates in the heating oven at 70 &#176;C for 1 h to remove the residual IPA.</li>
</ol>
2. Preparation of Compact TiO2 Layers (c-TiO2) to...

<ol>
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H., Palazzi, M., Rivet, J., Flahaut, J., C&#233;olin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Etude+du+Systeme+AgIBiI3.">Etude du Systeme AgIBiI3.</a> Materials Research Bulletin. 14 (3), 325-328 (1979).</li><li>Kondo, S., Itoh, T., Saito, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strongly+Enhanced+Optical+Absorption+in+Quench-Deposited+Amorphous+AgI+Films.">Strongly Enhanced Optical Absorption in Quench-Deposited Amorphous AgI Films.</a> Physical Review B. 57 (20), 13235-13240 (1998).</li><li>Kumar, P. S., Dayal, P. B., Sunandana, C. 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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+pH+on+Optic+and+Structural+Characterization+of+Chemical+Deposited+AgI+Thin+Films.">Effect of pH on Optic and Structural Characterization of Chemical Deposited AgI Thin Films.</a> Materials Research Ibero-American Journal of Materials. 20 (6), 1563-1570 (2017).</li><li>Chai, W. -. X., Wu, L. -. M., Li, J. -. Q., Chen, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Series+of+New+Copper+Iodobismuthates:+Structural+Relationships,+Optical+Band+Gaps+Affected+by+Dimensionality,+and+Distinct+Thermal+Stabilities.">A Series of New Copper Iodobismuthates: Structural Relationships, Optical Band Gaps Affected by Dimensionality, and Distinct Thermal Stabilities.</a> Inorganic Chemistry. 46 (21), 8698-8704 (2007).</li><li>Konstantatos, G., 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=Ultrasensitive+Solution-Cast+Quantum+Dot+Photodetectors.">Ultrasensitive Solution-Cast Quantum Dot Photodetectors.</a> Nature. 442, 180-183 (2006).</li><li>Mercier, N., Louvaina, N., Bi, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+Diversity+and+Retro-Crystal+Engineering+Analysis+of+Iodometalate+Hybrids.">Structural Diversity and Retro-Crystal Engineering Analysis of Iodometalate Hybrids.</a> CrystEngComm. 11 (5), 720-734 (2009).</li><li>Zhu, X. H., 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=Effect+of+Mono-+versus+Di-ammonium+Cation+of+2,2'-Bithiophene+Derivatives+on+the+Structure+of+Organic-Inorganic+Hybrid+Materials+Based+on+Iodo+Metallates.">Effect of Mono- versus Di-ammonium Cation of 2,2'-Bithiophene Derivatives on the Structure of Organic-Inorganic Hybrid Materials Based on Iodo Metallates.</a> Inorganic Chemistry. 42 (17), 5330-5339 (2003).</li><li>Zhu, H., Pan, M., Johansson, M. B., Johansson, E. M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+Photon-to-Current+Conversion+in+Solar+Cells+Based+on+Light-Absorbing+Silver+Bismuth+Iodide.">High Photon-to-Current Conversion in Solar Cells Based on Light-Absorbing Silver Bismuth Iodide.</a> ChemSusChem. 10 (12), 2592-2596 (2017).</li><li>Turkevych, 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=Photovoltaic+Rudorffites:+Lead-Free+Silver+Bismuth+Halides+Alternative+to+Hybrid+Lead+Halide+Perovskites.">Photovoltaic Rudorffites: Lead-Free Silver Bismuth Halides Alternative to Hybrid Lead Halide Perovskites.</a> ChemSusChem. 10 (19), 3754-3759 (2017).</li></ol>

The authors have nothing to disclose.

We have provided a detailed protocol for the solution fabrication of Ag-Bi-I ternary semiconductors, which are to be exploited as lead-free photovoltaic absorbers in thin-film solar cells with mesoscopic device architectures. c-TiO2 layers were formed on FTO substrates to avoid electron leakage flowing into the FTO electrodes. m-TiO2 layers were sequentially formed on c-TiO2-coated FTO substrates to improve the electron extractions generated from the photovoltaic absorbers (i.e.,...

Solution-processed inorganic thin-film solar cells have been widely studied by many researchers seeking to convert sunlight directly into electricity1,2,3,4,5. With the development of material synthesis and device architecture, lead halide-based perovskites have been reported to be the best solar cell absorbers with a power conversion efficiency (PCE) greater than 22%5. However, there are growing concerns about the use of toxic lead, as well as stability issues of lead-halide perovskite itself.
It has recently been reported that bismuth-based hybrid perovskites can be formed by incorporating monovalent cations into a bismuth iodide complex unit and that these can be used as photovoltaic absorbers in mesoscopic solar cell architectures6,7,8. The lead in the perovskites can be replaced with bismuth, which has the 6s2 outer lone pair; however, so far only conventional lead halide methodologies have been used for bismuth-based hybrid perovskites with complex crystal structures, despite the fact that they have different oxidation states and chemical properties9. In addition, these perovskites have poor surface morphologies and produce relatively thick films in the context of thin-film device applications; therefore, they have a poor photovoltaic performance with high band-gap energy (&#62; 2 eV)6,7,8. Thus, we sought to find a new method to produce bismuth-based thin-film semiconductors, which are environmentally friendly, air-stable, and have low band-gap energy (&#60; 2 eV), considering the material design and methodology.
We present solution-processed Ag-Bi-I ternary thin films, which can be crystallized to AgBi2I7 and Ag2BiI5, for lead-free and air-stable semiconductors10,11. In this study for the AgBi2I7 composition, n-butylamine is used as a solvent to simultaneously dissolve the silver iodide (AgI) and bismuth iodide (BiI3) precursors. The mixture is spin-cast and annealed at 150 &#176;C for 30 min in an N2-filled glove box; subsequently, the films are quenched to room temperature. The resultant thin films are brown-black in color. In addition, the surface morphology and crystal composition of the Ag-Bi-I ternary systems are controlled by the annealing temperatures and precursor ratio of AgI/BiI3. The resulting AgBi2I7 thin films exhibit a cubic phase crystalline structure, dense and smooth surface morphologies with large grains of 200 - 800 nm in size, and an optical band gap of 1.87 eV starting to absorb light from a wavelength of 740 nm. It has recently been reported that by optimizing the crystal compositions and device architecture, Ag-Bi-I ternary thin-film solar cells can achieve a PCE of 4.3%.

<table>
	<tbody>
		<tr>
			<td>Bismuth(III) iodide, Puratronic, 99.999% (metals basis)</td>
			<td>Afa Aesar</td>
			<td>7787-64-6</td>
			<td>stored in N2-filled condition</td>
		</tr>
		<tr>
			<td>Silver iodide, Premion, 99.999% (metals basis)</td>
			<td>Afa Aesar</td>
			<td>7783-96-2</td>
			<td>stored in N2-filled condition</td>
		</tr>
		<tr>
			<td>Butylamine 99.5%</td>
			<td>Sigma-Aldrich</td>
			<td>109-73-9</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma-Aldrich</td>
			<td>9002-93-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropyl alcohol (IPA)</td>
			<td>Duksan</td>
			<td>67-63-0</td>
			<td>Electric High Purity GRADE</td>
		</tr>
		<tr>
			<td>Titanium(IV) isopropoxide</td>
			<td>Sigma-Aldrich</td>
			<td>546-68-9</td>
			<td>&#8805;97.0%</td>
		</tr>
		<tr>
			<td>Ethyl alcohol</td>
			<td>Sigma-Aldrich</td>
			<td>64-17-5</td>
			<td>200 proof, ACS reagent, &#8805;99.5%</td>
		</tr>
		<tr>
			<td>Hydrochloric acid</td>
			<td>SAMCHUN</td>
			<td>7647-01-0</td>
			<td>Extra pure</td>
		</tr>
		<tr>
			<td>Titanium tetrachloride (TiCl4)</td>
			<td>sharechem</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>50nm-sized TiO2 nanoparticle paste</td>
			<td>sharechem</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>2-propanol</td>
			<td>Sigma-Aldrich</td>
			<td>67-63-0</td>
			<td>anhydrous, 99.5%</td>
		</tr>
		<tr>
			<td>Terpineol</td>
			<td>Merck</td>
			<td>8000-41-7</td>
			<td></td>
		</tr>
		<tr>
			<td>Heating oven</td>
			<td>WiseTherm</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Oxygen (O2) plasma</td>
			<td>AHTECH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>X-ray diffraction (XRD)</td>
			<td>Rigaku</td>
			<td></td>
			<td>Rigaku Miniflex 600 diffractometer with a NaI scintillation counter and using monochromatized Cu-K&#945; radiation 
			(1.5406 &#197; wavelength).</td>
		</tr>
		<tr>
			<td>Fourier transform infrared (FTIR)</td>
			<td>Bruker</td>
			<td></td>
			<td>Bruker Tensor 27</td>
		</tr>
		<tr>
			<td>field-emission scanning electron microscope (FE-SEM)</td>
			<td>Hitachi</td>
			<td></td>
			<td>Hitachi SU8230</td>
		</tr>
		<tr>
			<td>UV-Vis spectra</td>
			<td>PerkinElmer</td>
			<td></td>
			<td>PerkinElmer LAMBDA 950 
			Spectrophotometer</td>
		</tr>
		<tr>
			<td>Ultraviolet photoelectron spectroscopy (UPS)</td>
			<td>RBD Instruments</td>
			<td></td>
			<td>PHI5500 Multi-Technique system</td>
		</tr>
	</tbody>
</table>

solution-processed "silver-bismuth-iodine" ternary thin films for lead-free photovoltaic absorbers

Bismuth-based hybrid perovskites are regarded as promising photo-active semiconductors for environment-friendly and air-stable solar cell applications. However, poor surface morphologies and relatively high bandgap energies have limited their potential. Silver-bismuth-iodine (Ag-Bi-I) is a promising semiconductor for optoelectronic devices. Therefore, we demonstrate the fabrication of Ag-Bi-I ternary thin films using material solution processing. The resulting thin films exhibit controlled surface morphologies and optical bandgaps according to their thermal annealing temperatures. In addition, it has been reported that Ag-Bi-I ternary systems crystallize to AgBi2I7, Ag2BiI5, etc. according to the ratio of the precursor chemicals. The solution-processed AgBi2I7 thin films exhibit a cubic-phase crystal structure, dense, pinhole-free surface morphologies with grains ranging in size from 200 to 800 nm, and an indirect bandgap of 1.87 eV. The resultant AgBi2I7 thin films show good air stability and energy band diagrams, as well as surface morphologies and optical bandgaps suitable for lead-free and air-stable single-junction solar cells. Very recently, a solar cell with 4.3% power conversion efficiency was obtained by optimizing the Ag-Bi-I crystal compositions and solar cell device architectures.

It has been reported that the Ag-Bi-I ternary systems, which are regarded as promising semiconductors, are crystallized in various compositions, such as AgBi2I7, AgBiI4, and Ag2BiI510, according to the molar ratio of AgI to BiI3. Earlier studies have shown that bulk crystal forms with various compositions of Ag-Bi-I ternary systems can be experimentally synthesized by changing the molar ratio of AgI ...

Watch this Scientific Journal Video about Solution-Processed "Silver-Bismuth-Iodine" Ternary Thin Films for Lead-Free Photovoltaic Absorbers at JoVE.com

Solution-Processed &quot;Silver-Bismuth-Iodine&quot; Ternary Thin Films for Lead-Free Photovoltaic Absorbers

Herein, we present detailed protocols for solution-processed silver-bismuth-iodine (Ag-Bi-I) ternary semiconductor thin films fabricated on TiO2-coated transparent electrodes and their potential application as air-stable and lead-free optoelectronic devices.

Solution-Processed "Silver-Bismuth-Iodine" Ternary Thin Films for Lead-Free Photovoltaic Absorbers

Bismuth-based hybrid perovskites are regarded as promising photo-active semiconductors for environment-friendly and air-stable solar cell applications. ...

This method can help you answer key questions about how to make solution-processable silver-bismuth-iodine ternary semiconductors for environmentally friendly thin film solar cells and adopt applications. The main advantage of this technique is the solution fabrication of silver-bismuth-iodine which is then used as a lead-free photovoltaic absorber in thin film solar cells with a microscopic device architectures. This technique has potential applications in the production of environmentally-friendly thin film solar cells because the silver-bismuth-iodine ternary semiconductors are lead-free, air-stable photovoltaic absorbers.To begin preparing the precursor solution for compact titanium dioxide layers, place 8 milliliters of anhydrous ethanol in a 20 milliliter glass vial and start stirring it vigorously. Add 0.74 milliliters of titanium isopropoxide to the stirring ethanol dropwise. And then rapidly add 0.06 milliliters of concentrated hydrochloric acid.Stir the mixture for between 12 and 24 hours at room temperature to form the precursor solution. Next, sonicate a bare one inch by one inch FTO substrate for 15 minutes each in 2%aqueous octoxynol-9, acetone, and isopropyl alcohol. Dry the clean substrate in an oven at 70 degrees Celsius for one hour and let it cool to room temperature in air.Then, fix the substrate on a spin coater chuck. Fill a 1 milliliter or 3 milliliter syringe with compact titanium dioxide layer precursor solution and attach a 0.2 nanometer syringe filter. Filter the solution into a small vial.Apply 200 microliters of the filtered precursor solution to the substrate to fully cover it. Spin coat the substrate at 3000 RPM for 30 seconds. Anneal the film in an oven at 500 degrees Celsius for one hour.Then turn off the heat and let the substrate cool in air to room temperature, which usually takes about six hours. Next, immerse the coated substrate in an aqueous 0.12 molar solution of titanium tetrachloride. Soak the substrate in a 70 degree Celsius oven for 30 minutes.Thoroughly rinse the substrate in deionized water afterwards to remove residual titanium tetrachloride. Anneal the film at 500 degrees Celsius for one hour and then allow it to cool to room temperature in air. Once cool, store the compact titanium dioxide-coated substrate under nitrogen gas for later use.To begin preparing the precursor solution for a mesoporous titanium dioxide nanoparticle layer in a 5 milliliter glass vial, combine 0.5 grams of 50 nanometer titanium dioxide nanoparticle paste with 1.75 grams of isopropyl alcohol and 0.5 grams of terpineol. Add a stir bar to the vial and stir until the paste has completely dissolved. This usually takes about one hour.Next, fix a compact titanium dioxide-coated FTO substrate on a spin coater and apply 200 microliters of the nanoparticle solution to the substrate surface. Spin coat the substrate at 5000 RPM for 30 seconds. Anneal the coated substrate in an oven at 500 degrees Celsius for one hour and allow it to cool to room temperature.Then soak the substrate in an aqueous 0.12 molar solution of titanium tetrachloride at 70 degrees Celsius for 30 minutes. Thoroughly rinse the substrate with deionized water. Anneal it at 500 degrees Celsius for one hour and let it cool to room temperature in air.Store the substrate coated with compact and mesoporous titanium dioxide layers under nitrogen gas for later use. To begin preparing thin films of the silver iodobismuthate, silver dibismuth heptaiodide, in a nitrogen-filled glovebox at low humidity combine 0.3 grams of bismuth-three iodide, 0.06 grams of silver iodide, and 3 milliliters of n-butylamine. Vigorously vortex the mixture until the solids have mostly dissolved, and then syringe filter the precursor solution through a 0.2 micrometer polytetrafluoroethylene filter.Next, fix the desired substrate on a spin coater and apply 200 microliters of the filtered precursor solution. Spin coat the substrate at 6000 RPM for 30 seconds. Place the substrate on a hot plate and heat it to 150 degrees Celsius.Anneal the film at that temperature for 30 minutes and then quickly remove it from the hot plate to quench it. In a nitrogen-filled glove box, combine 10 milligrams of P3HT and 1 milliliter of chlorobenzene. Stir the mixture at 50 degrees Celsius for 30 minutes to completely dissolve the P3HT and then filter the mixture with a 0.2 micrometer PTFE syringe filter.Next, fix an FTO substrate coated with silver dibismuth hepatiodide on compact and mesoporous titanium dioxide on a spin coater. Apply 100 microliters of the P3HT solution to the substrate and spin coat the substrate at 4000 RPM or 30 seconds. Anneal the P3HT film on a hot plate preheated to 130 degrees Celsius for 10 minutes.Let the substrate cool to room temperature in the glove box. Lastly, use a thermal evaporator to deposit 100 nanometers of gold at 0.5 angstroms per second on the substrate to form the top gold contacts of the solar cell. silver-bismuth-iodine ternary thin films, 1:2, 1:1, and 2:1 molar ratios of silver iodide to bismuth-3 iodide were fabricated with this method.The 1:2 film showed a single peak at about 42 degrees, indiciating a cubic structure. Peak splitting was observed for the 1:1 and 2:1 films, indicating a hexagonal structure. The 1:2 film absorbed longer wavelengths than the 2:1 film did.Further, the 1:2 film had a smooth surface with large grains whereas particles of excess silver iodide were observed on the 2:1 film. The 1:2 film was thus chosen for further study. X-ray diffraction indicated that an annealing temperature of 150 degrees Celsius was required for the 1:2 film to crystallize entirely in the cubic phase.The film was stable in the air for at least 10 days. FTIR spectroscopies suggested that residual n-butylamine remained weakly complexed to bismuth-3 iodide and silver iodide at lower annealing temperatures, suppressing the formation of silver-bismuth-iodine building blocks. The grains became larger and more densely packed as the annealing temperature increased.Films annealed at 150 degrees Celsius also had the most suitable absorption properties for use in solar cells. Overall, the silver dibismuth heptaiodide film annealed at 150 degrees Celsius showed suitable energetic properties for solar cell use. This technique paves the way for researchers of solution-processable thin film solar cells to further develop methodologies for silver-bismuth-iodine ternary semiconductors in applications such as lead-free and air-stable thin film solar cells.While attempting this procedure, you may want to use controlled humidity of under 20%for spin coating the substrate with the silver-bismuth-iodine precursor solution. If you spin coat the precursor solution at or above 30%humidity, you will see yellowish because of the highly reactive and photo If you cannot control the humidity in the spin coater, you can spin coat the precursor solution in a N-filled glove box. However, please keep in mind that you must completely purge the glove box after it's done.

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JoVE Journal

Chemistry

9.5K Views.  Daegu Gyeongbuk Institute of Science and Technology (DGIST). This method can help you answer key questions about how to make solution-processable silver-bismuth-iodine ternary semiconductors for environmentally friendly thin film solar cells and adopt applications. The main advantage of this technique is the solution fabrication of silver-bismuth-iodine which is then used as a lead-free photovoltaic absorber in thin film solar cells with a microscopic device architectures. This technique has potential applications in the production of environmentally-f...