Perovskite solar cells (PSCs) have emerged as a new-generation photovoltaic technology that features both low manufacturing cost and high power conversion efficiencies (PCEs) [1-3].In the past decade,the PCEs of PSCs have increased from 3.8% to 25.5%,which are now comparable to those of silicon-based solar ceils.Neverthe-less,by comparing the detailed device parameters of record PSCs reported at different times,Peng et al.found that although the open circuit voltage (Voc) increases steadily over the past years,the fill factor (FF) has seen a plateaue,as shown in Fig.1(a and b).[3] The high Voc can be mainly attributed to reduced nonradia-tive recombination especially at the perovskite/charge transport layer interfaces,while FF is influenced by both charge transport efficiency and recombination losses [1,3].