Ultrafast Interfacial Charge Transfer of Cesium Lead Halide Perovskite Films CsPbX3 (X = Cl, Br, I) with Different Halogen Mixing

Understanding the interfacial charge transfer of the photoinduced transients of all-inorganic cesium lead halide perovskites (CsPbX3; X = Cl, Br, I) is critical for their photovoltaic applications. Ultrafast dynamics can provide comprehensive information about the transient behavior of the carriers and their transfer mechanism in the materials. In this work, the interfacial charge transfer of CsPbX3 films assembled with TiO2 with different halogen doping ratios was studied using femtosecond transient absorption spectroscopy combined with global analysis. Four subsequent decay processes after photoexcitation were carried out, including hot carrier cooling, free exciton formation, electron transfer, and charge recombination. The results indicate that the time constant of the interfacial electron transfer varies with the location of the trap state of these perovskites and the relative energy of conduction bands in the perovskite and TiO2 and that the time constant of the charge recombination can be attributed to the electron–hole interactions. These interpretations are supported by calculations based on first-principles density functional theory. Higher iodine doping in such perovskite CsPbX3/TiO2 systems increases the time constants of the electron transfer and charge recombination, which suggests that all-inorganic perovskite CsPbX3 with a high iodine content is favorable for improving the power conversion efficiency of solar cells.