Ultrahigh fill-factor all-inorganic CsPbBr3 perovskite solar cells processed from two-step solution method and solvent additive strategy

All-inorganic CsPbBr3 perovskite solar cells (PSCs) have attracted more attentions due to the excellent environmental stability, however, the wide bandgap and relatively poor crystallinity of CsPbBr3 have been the main obstacle to improve their power conversion efficiency (PCE). Herein, we proposed an efficient and simple strategy of precursor additive in the two-step aqueous-solution method, the resulted CsPbBr3 film has achieved more uniform grain size, almost pure perovskite phase, smoother surface, less defects, enhanced light absorption and longer carrier lifetime. This is due to the rapid evaporation of additive (IPA and CH3OH) in the CsBr/H2O precursor leads to a relatively higher local CsBr concentration on the surface of PbBr2, which can provide more nucleation sites and accelerate the crystallization of perovskite. Further, when utilizing the optimal additive of 5% (in volume) IPA, the HTM-free carbon-based CsPbBr3 PSCs obtained a PCE improvement from 9.09% to 10.29%, and an ultrahigh fill factor (FF) of 85.21%. What is more, by adding 0.1 mol/L PbCl2 into the PbBr2 solution in the first step, the open circuit voltage of device has increased from 1.36 V to 1.48 V, the champion PCE reached 10.37% (steady output PCE of 10.17%), and the non-encapsulated device could maintain 85% of its initial efficiency after 50 d in the air. This work provides a cost-effective approach to grow CsPbBr3 film and boosts the efficiency benchmark of the CsPbBr3 PSCs to more than 10%, it is desirable that the highly efficient and stable CsPbBr3 PSCs can be developed in future.