Mixing of Azetidinium in Formamidinium Tin Triiodo Perovskite Solar Cells for Enhanced Photovoltaic Performance and Great Stability in Air.

Abstract

Overcoming the issue of stability of tin-based perovskites is a main challenge for the commercial development of lead-free perovskite solar cells. To tackle this problem, a new organic cation, azetidinium (AZ), is incorporated into the crystal structure of formamidinium tin triiodide (FASnI 3 ) to form mixed cation perovskite AZ x FA 1- x SnI 3 . As AZ has a similar size but a larger dipolar moment than FA, the hybrid AZ x FA 1- x SnI 3 films exhibit varied optical and electronic properties upon increasing the proportion of AZ. Trifluoromethylbenzene (CF 3 C 6 H 5 ) served as antisolvent to fabricate smooth and uniform perovskite films for the devices with an inverted planar heterojunction structure. The device performance was optimized to produce the best efficiency at x = 0.15 (AZ15), for which efficiency 9.6% of power conversion was obtained when the unencapsulated AZ15 device was stored in air for 100 h; the device retained 90% of its initial efficiency for over 15 days. The great performance and stability of this device reveal that the concept of mixed cations is a promising approach to stabilize tin-based perovskite solar cells for their future commercialization.