Interfacial modulation by ammonium salts in hole transport layer free CsPbBr3 solar cells with fill factor over 86 %

CsPbBr3-based perovskite solar cells (PSCs) are potential candidates for the next-generation photovoltaic technology owing to their robust stability. Nevertheless, the inorganic CsPbBr3 PSCs using carbon electrode without hole transport layer usually suffer from severe non-radiative recombination loss at CsPbBr3/Carbon interfaces, thereby generating low fill factors (FFs) and further limiting the improvement of power conversion efficiencies (PCEs). To circumvent this issue, we proposed a universal interfacial engineering strategy to reduce the trap-assisted recombination through depositing butylammonium bromide (BABr) on the surface of CsPbBr3 films, which would enhance the FF and subsequent PCE of inorganic PSCs. The experimental results illustrate that the BABr modification could not only improve the morphology and phase purity of the inorganic perovskite films, but also adjust the energy level alignment between the CsPbBr3 layer and carbon electrode. After the optimization of BABr concentrations, we fabricated the BABr-modified device delivered an impressive PCE of 9.86 % with an extreme high FF over 86 %, which is one of the highest values achieved among the reported inorganic PSCs. Moreover, the PCE of unsealed CsPbBr3 device with BABr exhibited almost no attenuation after 90 days storage under the ambient atmosphere.