Rational Selection of Phenethylammonium Salts for 2D/3D Tin Perovskite Solar Cells: The Halogen Ion Matters

Tin perovskite solar cells have attracted extensive attention in recent years for developing lead-free perovskite photovoltaics. Introducing phenethylammonium salts (PEAX, X = I, Br, Cl) has been demonstrated to be an effective way for regulating the crystallization and dimensionality of tin perovskite films, thus yielding 2D/3D perovskite solar cells with improved performance. However, the impact of different halogen ions in PEAX on the photovoltaic performance has not been uncovered. Herein, we comparatively investigate the effects of different halogen ions in PEAX on the tin perovskite films and their photovoltaic performance. It is found that by incorporating PEACl, instead of PEAI and PEABr, a more compact and smoother perovskite film with decreased pinholes and increased crystallinity is obtained, thereby significantly suppressing the nonradiative recombination and benefiting the charge transport. The PEACl incorporated device exhibits significantly mitigated open-circuit voltage (V_oc) loss and dramatically increased power conversion efficiency (PCE). Besides, increasing the PEACl concentration to 25% further improves the morphology of tin perovskite film, leading to increased V_oc without sacrificing the photocurrent. The 2D/3D tin perovskite solar cells optimized by adding 25% PEACl exhibit a good stability in nitrogen atmosphere, and a champion PCE of 11.5% is achieved, which significantly surpasses that of the control device.