Revealing the Band Structure of FAPI Quantum Dot Film and Its Interfaces with Electron and Hole Transport Layer Using Time Resolved Photoemission

Lead halide perovskite nanocrystals have attracted attention in the field of nanocrystal based light emitting diodes and solar cells, because their devices showed high performances in only a few years. Among them, CsPbI3 is a promising candidate for solar cell design in spite of a too wide band gap and severe structural stability issue. Its hybrid organic-inorganic counterpart (NH2)2CHPbI3 (FAPI), where the Cs is replaced with formamidinium (FA), presents a smaller band gap and also an improved structural stability. Here, we have investigated the energy landscape of pristine FAPI, and the interface of FAPI with electron and hole selective layers using transport, photoemission, and non-contact surface photovoltage by means of time-resolved photoemission. We have found from transport and photoemission that its Fermi level is deeply positioned in the band gap, enabling the material to be almost intrinsic. Time-resolved photoemission has revealed that the interface of pristine FAPI is bended toward downward s...