Understanding the Defect Properties of Quasi-2D Halide Perovskites for Photovoltaic Applications

Quasi-2D halide perovskites have emerged as some of the most promising photovoltaic materials owing to their excellent stability, yet the device power conversion efficiency is far from satisfactory. Besides crystal orientation-related carrier transport, defects in absorbers also play a crucial role in device performance, which has received limited attention in the 2D perovskite field. Herein, we systematically profile the defect states in 2D perovskite film by the temperature-dependent admittance spectroscopy (AS), light intensity-dependent V_OC, space-charge-limited-circuit (SCLC), and photoluminescence measurements. It is revealed that the quasi-2D perovskite films suffer from severe defects as compared to the 3D counterparts in terms of both trap energy levels and trap densities. Consequently, the level of nonradiative recombination of photogenerated carriers is much greater in the corresponding devices, wherein the monomolecular recombination is dominant. These findings substantially contribute to a deeper understanding of the nature of 2D perovskite materials, which promotes the further development of 2D perovskite solar cells.