Unraveling the degradation process of 2D passivated and Cs stabilized FAPbI 3 by optical pump THz probe spectroscopy

Abstract

The carrier dynamics and time-dependent photo-physical properties in the degradation period of hybrid organic-inorganic lead halide perovskites (HOIPs) are still unclear. Here a non-contact optical pump THz probe measurement was performed to observe the long-term degradation process of 2D passivated and cesium stabilized formamidinium lead iodide perovskite (FAPbI 3 ) films. We find that photoconductivity and carrier mobility of the FA 0.9 Cs 0.1 PbI 3 film decay steadily, while these of the 2D phenylethylammonium lead iodide (PEA 2 PbI 4 ) passivated FAPbI 3 film show an accelerated decay rate. Moreover, it’s also revealed that the localization of charge carriers increases with the transformation process from the fitted results by the Drude-Smith model. These results indicate that the stabilized effect of Cs incorporation is continuous, while the passivated effect of PEA 2 PbI 4 can be weakened by the newly emerged phase boundaries. This report proposes a new perspective and sheds light on the degradation process of HOIPs.