Elucidating the Spatial Dynamics of Charge Carriers in Quasi-Two-Dimensional Perovskites
Dohyung Kim, Mahshid Ahmadi
Abstract
Quasi-two dimensional (2D) organic–inorganic hybrid perovskites (OIHPs) have shown better ambient stability with decent solar cell performances. However, the power conversion efficiency of quasi-2D OIHPs is still below that of 3D polycrystalline perovskites. To understand the limitation of quasi-2D OIHPs, we explore charge carrier properties in 3D and quasi-2D perovskites using advanced scanning probe microscopy techniques. Kelvin probe force microscopy (KPFM) identifies slow degradation in quasi-2D perovskites by measuring photovoltage variations under thermal and humid conditions. Bias-driven photocurrent maps obtained by conductive-atomic force microscopy (c-AFM) measurements reveal local inhomogeneous conduction and hysteretic currents in quasi-2D perovskites while relatively uniform conductivity is observed on individual grains in the 3D perovskite counterparts. In addition, bias-driven KPFM and I–V measurements in the lateral Au electrode devices show higher charge carrier dynamics with stronger potential drop at the interfaces in the 3D perovskite than those of the quasi-2D perovskite devices. The combination of c-AFM and KPFM results confirm less ionic conduction in the quasi-2D perovskites as compared to the 3D perovskites. Our study elucidates underlying mechanisms behind the lower efficiency of quasi-2D perovskites, which is necessary for further development of efficient and stable perovskite-based devices.