Perovskite solar cells composed of organic-metal-halide materials have made remarkably progress in just a few years with power conversion efficiencies from 3.8%¹ in 2009 to a certified 22.1%² in 2016. Following from the traditional structure of dye-sensitized solar cells, n-type semiconductor anatase TiO₂ mesoporous layer was commonly used for delivering high power conversion efficiency for perovskite solar cells. However, disadvantages of the TiO₂ mesoporous structure is that it requires a high-temperature (>450ºC) sintering process to improve the interconnection among the nanoparticles³ and burn out the organic binders in paste. Furthermore, the position of conduction band edge between anatase TiO₂ to organo-lead-halide perovskite is ~0.1 eV⁴ which is not satisfyingly enough for electron transfer. Inorganicmetal oxides such as SnO₂ is generally used as n-type semiconductor for electronic devaises such as display, which have a deeper conduction band edge than anatase TiO₂ and higher mobility of up to 240 cm² /(V · s). Thus, it could perform more efficient electron transfer from perovskite to electron transport layers, and elimination of hysteresis on the J–V curve due to the enhanced electron extraction by reduction of the energy barrier at the perovskite/electron transportation layer interface.⁵ In this studies, we report perovskite solar cells structured with SnO₂ compact layer made by spray pyrolysis and nano particles mesoporous layer as electron selective layers and its less hysteresis J–V curve. A superior SnO₂ compact layer was prepared from tin tetrachloride (SnCl₄) solution on the several annealing temperature, and then following with spin-coating SnO₂ nanoparticles solution onto compact layer to fabricate the mesoporous SnO₂ layer in ambient air condition; furthermore, it was annealed under 180ºC for 30 min. By combining with a triple cation perovskite layer of formamidinium, methylammonium and cesium and optimized SnO₂ layers, the resulting best performance of our devices were reached 1.16 V as open circuit voltge, 21.8 mA cm^-2 as short circuit current, 72% as fill factor, and 18.1% as power conversion efficiency.

Reference

1. A. Kojima, K. Teshima, Y. Shirai, et al., J. Am. Chem. Soc., 2009, 131, 6050–6051.

2. NREL: National Center For Photovoltaics Home Page. http:// www.nrel.gov/ncpv, Accessed July 30, 2016.

3. M. M. Lee, J. Teuscher, T. Miyasaka, et al., Science, 2012, 338, 643–647.

4. J. P. C. Baena, L. Steier, W. Tress, et al., Energy Environ. Sci., 2015, 8, 2928–2934.

5. Q. Jiang, L. Zhang, H. Wang, et al., Nature Energy, 2016, 2, 16177.