Unraveling the degradation process of 2D passivated and Cs stabilized FAPbI3 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 (FAPbI3) films. We find that photoconductivity and carrier mobility of the FA0.9Cs0.1PbI3 film decay steadily, while these of the 2D phenylethylammonium lead iodide (PEA2PbI4) passivated FAPbI3 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 PEA2PbI4 can be weakened by the newly emerged phase boundaries. This report proposes a new perspective and sheds light on the degradation process of HOIPs.