Influence of charge transport layer on the crystallinity and charge extraction of pure tin-based halide perovskite film

Tin-based halide perovskite have emerged as a promising alternative to toxic lead-based halide perovskite for next generation photovoltaic device. In order to reveal the effect of charge transport layers (CTLs) on the crystallinity and charge extraction of tin-based halide perovskite film, here we employ different electron transport materials and hole transport materials as CTLs used for perovskite film growth. The tin-based halide perovskite films grown on organic CTLs exhibit better crystallization, lower lattice strain and have less defect states than those grown on inorganic CTLs, and photogenerated hole seems easier to be extracted than electrons in tin-based halide perovskite films. The former one can explain very well why the inverted structure tin-based perovskite solar cells show much higher power conversion efficiency (PCE) compared to the regular structure device. The later one suggests balanced electron and hole extraction are needed for enhancing the photovoltaic performance of the tin-based perovskite solar cell. Furthermore, the carrier extraction rate at CTLs/perovskite interface not only depends on the band offset of the CTLs/perovskite interface but also can be affected by the free energy of coulombic interaction at the interface. These finding would shed light on the further improvement of tin-based perovskite solar cells.