Direct Observation of Charge Injection From CH3NH3PbI3−xClx to Organic Semiconductors Monitored With sub‐ps Transient Absorption Spectroscopy

Abstract

Thin films of the hybrid perovskite CH3NH3PbI3−xClx are prepared in contact to poly(3,4‐ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS) or phenyl‐C61‐butyric acid methyl ester (PCBM) as model interfaces relevant in inverted perovskite solar cells (IPSCs) which provide some significant advantages over the established mesoporous cell concepts. Pump–probe absorption spectroscopy with femtosecond resolution is used to analyze injection of photo‐generated charge carriers from the perovskite to the PEDOT:PSS and PCBM layers by directly monitoring characteristic spectroscopic signatures of charge carriers in these contact phases. Such signal is identified for holes injected into the PEDOT:PSS layer, which appeared within the resolution of the measurement setup (<200 fs) proving ultrafast hole injection. Changes in the transient signals characteristic for the perovskite layer as reflected in the time constants obtained by global analysis confirmed this observation. Ultrafast injection of electrons into PCBM is also found based on the decay of signals characteristic for the excited state of the perovskite as well as by newly arising signals assigned to injected electrons into PCBM. Efficient injection of charge carriers following excitation of the perovskite film to both organic electron and hole conductors is thereby directly shown.