Excitation Wavelength Dependent Interfacial Charge Transfer Dynamics in a CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> 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 5ms 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.