Tracking and Extraction of Charge Carriers through Dissociation of Excitons in Cesium Lead Halide Perovskite Using Tin Dioxide

Abstract

Lead halide perovskites are governing interest in optoelectronics owing to their superior photophysical properties. The performances in the device depend on the extent of charge carrier extraction and separation of excitons; however, because of the complicacy of the device architect, the real-time monitoring of the charge carrier is challenging. In this work, by employing the steady-state and time-resolved techniques in terms of optical absorption and photoluminescence (PL) measurements, the exploration and deciphering of the photoexcited charge carrier extraction from cesium lead bromide (CsPbBr₃) perovskite using tin dioxide (SnO₂) as an electron transporting layer is reported. Adopting the thermal evaporation method, a homogeneous qualitatively controlled ∼15 nm-thick CsPbBr₃ is fabricated on a previously made SnO₂ on an indium-doped tin oxide (ITO) substrate. Steady-state PL implies quenching of CsPbBr₃ luminescence in the presence of SnO₂, which is further supported by the faster decay in time-correlated single photon counting measurements. The tracking of the charge carrier is directly probed by monitoring the ground-state bleach (GSB) dynamics in different side excitations through pump–probe measurement in femtosecond time resolution. The dynamics are fitted with exponential function, and the early rise in GSB is attributed to hot carrier cooling time. The following time constants represent charge extraction (when CsPbBr₃ is measured with SnO₂) and recombination. A faster time constant in lifetime values indicates fast charge extraction when the excitation is performed from the extracting layer side. The first-principles calculations using density functional theory (DFT) reveal significant charge rearrangement at the CsPbBr₃/SnO₂ interface, forming an internal electric field that drives carrier extraction. Our investigation highlights the simplest approaches to dissociation of the excitons and real-time tracking of charge carriers in thin-film perovskite and electron transporting layer interfaces.