Ambient-Air-Stable Lead-Free CsSnI<sub>3</sub> Solar Cells with Greater than 7.5% Efficiency
Tao Ye, Ke Wang, Ke Wang, Yu Hou, Dong Yang, Nicholas J. Smith, Brenden A. Magill, Jungjin Yoon, Rathsara R. H. H. Mudiyanselage, Giti A. Khodaparast, Kai Wang, Kai Wang, Shashank Priya
Abstract
Black orthorhombic (B-γ) CsSnI3 with reduced biotoxicity and environmental impact and excellent optoelectronic properties is being considered as a promising eco-friendly candidate for high-performing perovskite solar cells (PSCs). A major challenge in a large-scale implementation of CsSnI3 PSCs includes the rapid transformation of Sn2+ to Sn4+ (within a few minutes) under an ambient-air condition. Here, we demonstrate that ambient-air stable B-γ CsSnI3 PSCs can be fabricated by incorporating N,N′-methylenebis(acrylamide) (MBAA) into the perovskite layer and by using poly(3-hexylthiophene) as the hole transporting material. The lone electron pairs of −NH and −CO units of MBAA are designed to form coordination bonding with Sn2+ in the B-γ CsSnI3, resulting in a reduced defect (Sn4+) density and better stability under multiple conditions for the perovskite light absorber. After a modification, the highest power conversion efficiency (PCE) of 7.50% is documented under an ambient-air condition for the unencapsulated CsSnI3-MBAA PSC. Furthermore, the MBAA-modified devices sustain 60.2%, 76.5%, and 58.4% of their initial PCEs after 1440 h of storage in an inert condition, after 120 h of storage in an ambient-air condition, and after 120 h of 1 Sun continuous illumination, respectively.