Name: solution-processed "silver-bismuth-iodine" ternary thin films for lead-free photovoltaic absorbers
Uploaded: 2018-09-27T14:45:00
Description: Watch this Scientific Journal Video about Solution-Processed "Silver-Bismuth-Iodine" Ternary Thin Films for Lead-Free Photovoltaic Absorbers at JoVE.com

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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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 "Silver-Bismuth-Iodine" 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.

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

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