Slow Hot-Carrier-Cooling in a 2D Lead-Iodide Perovskite Film and Its Photovoltaic Device

Significantly slow hot-carrier-cooling happens in a multiphase quasi two-dimensional (2D) perovskite film of (BA)2(FA)n−1PbnI3n+1, where BA is butylammonium, FA is formamidinium, and n = 3 nominally. Due to this phenomenon, a linearly polarized multi-peak emission from phases of n = 2, 3, and 4 emerges and the ever-present one from n = ∞ phase blue-shifts in the photoluminescence (PL) spectra, excited using a nanosecond pulsed laser with increasing excitation intensities. Furthermore, hot-carrier PL from small n materials also emerges using a continuous wave laser with an intensity of ∼100 mW/cm2; consequently, the abnormal enhancement of the open-circuit voltage through hot-carrier extraction above 300 mW/cm2 is achieved. Our work may prove that the FA-based 2D perovskite gives a direction to fabricating hot-carrier solar cells that potentially boost the power conversion efficiency.