Power conversion efficiency (PCE) of lead halide perovskites (LHPs) has rapidly climbed above 27% mark with perovskite-silicon tandem solar cell, which has drawn great attention from the research community. However, the fundamental understanding on the working mechanism and the role of structure responsible for this excellent PCE is still lacking. It has already been recognized that light-induced structural deformation acts a critical role in photovoltaic and optoelectronic properties of LHPs devices [1-7]. By employing synchrotron X-ray transient absorption spectroscopy (Laser pump-X-ray probe) with the atomic resolution across the full time scale from ps to µs [8,9], we have directly observed the formation of photoinduced self-trapped hole polaron in two prototypical but popular perovskite thin film samples: MAPbBr3 and FAPbBr3, in which the photoinduced holes are quickly self-trapped at Br atoms by distorting the local structure around Br sites to form the Br2 dimer (Vk center). We have also found that the hole polaronic state in FAPbBr3 is much longer alive compared to MAPbBr3 possibly because FA cations give less freedom to [PbBr6] octahedral units for their structural relaxation. This self-trapped hole polaron formation should alter the charge carrier transport and it might be responsible for some abnormal behaviors such as photovoltaic hysteresis in perovskite solar cells. Our results will contribute to the rational design of LHPs devices for advancing their PCE in photovoltaic devices. The observed novel structure-function correlation will open up new opportunity for advanced device functionalities, such as charge storage, light emitting devices.

Direct observation of photoinduced self-trapped hole polaron formation in perovskites

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.