Date Published: March 25, 2018
Publisher: John Wiley and Sons Inc.
Author(s): Yonghui Lee, Seunghwan Lee, Gabseok Seo, Sanghyun Paek, Kyung Taek Cho, Aron J. Huckaba, Marco Calizzi, Dong‐won Choi, Jin‐Seong Park, Dongwook Lee, Hyo Joong Lee, Abdullah M. Asiri, Mohammad Khaja Nazeeruddin.
Planar perovskite solar cells using low‐temperature atomic layer deposition (ALD) of the SnO2 electron transporting layer (ETL), with excellent electron extraction and hole‐blocking ability, offer significant advantages compared with high‐temperature deposition methods. The optical, chemical, and electrical properties of the ALD SnO2 layer and its influence on the device performance are investigated. It is found that surface passivation of SnO2 is essential to reduce charge recombination at the perovskite and ETL interface and show that the fabricated planar perovskite solar cells exhibit high reproducibility, stability, and power conversion efficiency of 20%.
Device Fabrication: FTO glass (Nippon Sheet Glass) substrates were partially etched with Zn powder and diluted HCl solution, and sequentially cleaned with detergent solution, water, and ethanol. ALD SnO2 films were prepared with tetrakis‐dimethyl‐amine tin as a Sn precursor and ozone as an oxygen reactant.22 The deposition of ALD SnO2 was carried out at 120 or 100 °C, and the films were used as‐prepared or after postannealing. For Type 1 passivation, a compact TiO2 layer was coated on the cleaned FTO substrate by spray pyrolysis deposition at 450 °C with a precursor solution prepared by diluting titanium diisopropoxide (Sigma‐Aldrich) in ethanol. The PTO layer was formed on a c‐TiO2‐coated FTO films by ALD. The deposition was carried out at 100 °C, and the as‐prepared film was postannealed at 180 °C for 1 h. A thin layer of SnO2 nanoparticles was prepared by spin coating the SnO2 colloid precursor (Alfa Aesar, ≈2.7%). The SnO2 layer was spin coated at 4000 rpm for 30 s, and heat‐treated in the air at 150 °C for 30 min.28 The (FAPbI3)0.85(MAPbBr3)0.15 precursor solution was prepared by mixing PbI2 (1.10 m, TCI), FAI (1.05 m, Dyesol), PbBr2 (0.185 m, TCI), and MABr (0.185 m, Dyesol) in a mixed solvent of DMF:DMSO = 4:1 (volume ratio). The solution was spin coated at 1000 rpm for 10 s and, continuously at 5000 rpm for 30 s. During the second step, 100 µL of chlorobenzene was poured on the film at 15 s. Films are postannealed at 100 °C for 60 min. The HTM solution was prepared by dissolving 10 mg of PTAA (Emindex) with additives in 1 mL of toluene. As additives, 7.5 µL of Li‐bis(trifluoromethanesulphonyl) imide (Aldrich) from the stock solution (170 mg in 1 mL of acetonitrile), and 4 µL of 4‐tert‐butylpyridine were added. The HTM layer was formed by spin coating the solution at 3000 rpm for 30 s, and followed by the deposition of the 70 nm thick Au electrode by a thermal evaporation.
The authors declare no conflict of interest.