Photophysics of organic-inorganic hybrid perovskite solar cells

Abstract

Organic-inorganic hybrid perovskites are attracting much attention as photoabsorbers for high-efficiency thin film solar cells. For further improvement of the device performance, the photophysics in the actual devices have to be clarified. Here, we studied carrier recombination and extraction dynamics in CH3NH3PbI3 perovskite solar cells using time-resolved photoluminescence (PL) and photocurrent (PC) measurements. It was found that the PL lifetime of the perovskite layer in the solar cell devices becomes longer with increasing excitation intensity, which is the exact opposite of the trend observed for the bare perovskite thin films. This slowdown of the PL decay reflects the bottleneck effect in the carrier extraction process at the interface, which also reduces the external quantum efficiency for PC. We clarified that the dynamical change of the carrier extraction efficiency plays an important role in the carrier recombination and transport in the perovskite solar cells. We successfully reproduced the experimental excitation intensity dependence by numerical simulations based on a simple model including carrier recombination and extraction processes. Furthermore, we performed microscopic imaging of PL and PC from CH3NH3PbI3 solar cells. The observed negative correlation between the PL and PC intensities reflects the competition between radiative recombination and carrier extraction processes. Our simultaneous measurement of PL and PC provides essential information to establish high-performance devices. This allows us to analyze the photocarrier dynamics in the lead-free CH3NH3SnI3 solar cells.