Instantaneous Photocarrier Transport at the Interface in Perovskite Solar Cells to Generate Photovoltage

Abstract

The instantaneous photocarrier transport of perovskite solar cells was evaluated by assessing laser-induced terahertz (THz) emission to understand carrier dynamics in perovskite solar cells. The waveform of laser-induced THz radiation from an interface between the TiO2 electron transport layer and perovskite active layer of an n-i-p perovskite solar cell with varying external bias was measured using THz-time domain spectroscopy. The amplitude of the THz radiation decreased with increasing reverse bias voltage. The waveform of the THz radiation was inverted at a strong reverse bias. The measured bias voltage dependence suggests that the transient current generated at the interface between perovskite and TiO2 owing to the higher mobility of electrons than that of holes, namely the photo-Dember effect, is the dominant source of THz radiation and the destructive contribution of the interfacial electric field inverts the transient current when a reverse bias causes a strong interfacial electric field. The significant contribution of the interfacial electric field has not been previously reported in perovskite thin films and is unique to solar cells. We believe that band bending at interfaces in perovskite solar cells will be determined from the THz emission with proper modeling.