Dark excitons and long-lived, light-induced defect states in (EPEA)2PbI4

The 2D Ruddlesden- Popper perovskite (EPEA)2PbI4 was investigated using temperature - and power -dependent PL and TA spectroscopy. This endeavor revealed the presence of multiple excitonic complexes in these materials, with signatures of carrier redistribution mediated by power and/or temperature, and the presence of extremely long-lived dark states in TA. These states appear to be light -induced defects which heal after illumination ceases. As such, they bring new insight into failure mechanisms and material design approaches in perovskite photovoltaics