Excitation wavelength dependent interfacial charge transfer dynamics in a CH3NH3PbI3 perovskite film

Abstract

Elucidation of interfacial charge separation and recombination mechanisms is crucial to improve performance of organic-inorganic metal halide perovskite solar cells. Here, we have investigated influence of initially populated electron and hole potential levels in a perovskite conduction band (CB) and valence band (VB), respectively, by altering an excitation wavelength on interfacial charge separation and recombination dynamics in a CH3NH3PbI3 perovskite film sandwiched by a mesoporous TiO2 structure as an electron transport material (ETM) and a spiro-OMeTAD film as a hole transport material (HTM). Multi-phasic electron injection reactions are observed over <1.2 to several tens of nanoseconds, while most of holes are injected to a spiro-OMeTAD layer within the transient emission spectroscopy instrument response time (1.2 ns). In contrast, interfacial charge recombination rates are slower (from 5 ms to 1.3 s) with the increase of the excitation wavelength. These kinetics suggest that as long as low excitation intensity is employed, e.g. 10 nJ/cm2 or 1 sun (100 mW/cm2), the APCE of ~100% can be expected at any excitation wavelength for the solar cells based on FTO/c-TiO2/m-TiO2/MAPbI3/OMeTAD films.