Dimensionality Control of SnO2 Films for Hysteresis-Free, All-Inorganic CsPbBr3 Perovskite Solar Cells with Efficiency Exceeding 10.

Abstract

The all-inorganic cesium lead bromide (CsPbBr3) perovskite solar cells (PSCs) have attracted considerable interest because of their outstanding environmental stability and low manufacturing cost. However, the state-of-the-art mesoscopic titanium dioxide (TiO2) electron-transporting layers (ETLs) always present low electron mobility, are destructive to perovskites under ultraviolet light illumination, as well as possess high sintering temperature. Nanostructured tin dioxide (SnO2) is a promising electron-transporting material for high-efficiency PSCs due to matching energy-level alignment with the perovskite layer, improved optical transparency, high electron mobility, excellent photostability, and low-temperature processing. Furthermore, rapid but poorly controlled perovskite crystallization makes it difficult to scale up planar PSCs for industrial applications. To address this issue, we adopt a dimensional SnO2 ETL to change the surface wettability for uniform perovskite coverage over large areas and the growth of large-sized CsPbBr3 grains, resulting in a maximum grain size of 1.65 μm. Moreover, the dimensional SnO2 ETL could increase the interfacial contact area between the CsPbBr3 layer and the ETL and enhance the electronic contact for efficient electron extraction to suppress or to eliminate the notorious hysteresis behavior. As expected, a power conversion efficiency (PCE) of 9.51% with an almost hysteresis-free phenomenon is achieved through dimensionality control of SnO2 films attributed to the remarkably enhanced light harvesting, accelerated electron extraction, diminished defect density, and reduced charge recombination. Upon further interfacial modification with graphene quantum dots (GQDs), the PSC based on the two-dimensional SnO2 ETL achieves a champion PCE of 10.34% due to the improved energy-level alignment at the device interface. Moreover, the best all-inorganic CsPbBr3 PSC free of encapsulation retains 93% of initial efficiency over 10 days at 80% relative humidity. This work provides an effective dimensionality control strategy for optimized charge transportation and enlarged perovskite grain size to make stable and efficient all-inorganic CsPbBr3 PSCs.