Effect of binary additives in mixed 2D/3D Sn-based perovskite solar cells

Abstract

Additive doping improves the morphology and stability of tin (Sn)-based perovskite films under ambient conditions. However, the role of additives in the perovskite layer is not clearly understood, especially when two or more additives are incorporated. In this study, the effect of binary additives composed of 2-phenylethylammonium iodide (PEAI) and ethylenediammonium diiodide (EDAI2) on formamidinium tin iodide (FASnI3) perovskite solar cells (PSCs) is studied. PEAI plays an important role in reducing the dimensionality of the perovskite crystals from 3D to mixed 2D/3D, whereas EDAI2 resides on the grain periphery as a linker to improve the interconnection between neighboring grains. Overall, the optimum blending of the two additives, 8 and 1 mol % of PEAI and EDAI2, produces pinhole-free, compact perovskite film with superior crystallinity and preferential orientation, exhibiting very low background charge carrier density, reduced trap states and suppressed recombination losses. The reduced dimensionality and favored perovskite layer stacking lead to a better interlayer coupling that improves charge transfer at the interfaces. Consequently, the best PSC exhibits a power conversion efficiency (PCE) of 8.47% with an open-circuit voltage (VOC) of 0.634 V and the device stability is enhanced up to 5 days in ambient conditions without any additional encapsulation.