A Smart Way to Prepare Solution‐Processed and Annealing‐free PCBM Electron Transporting Layer for Perovskite Solar Cells

Abstract As a state‐of‐the‐art n‐type material, PC 61 BM ((6,6)‐phenyl C61 butyric‐ methylester) has been largely used as the top electron transporting layer (ETL) in inverted perovskite solar cells (PSCs). Whereas so far, there have been few reports on using pristine PC 61 BM as the bottom ETL in conventional (n‐i‐p‐type) PSCs, because it will be partially dissolved by the perovskite precursor solution (such as N , N ‐Dimethylformamide and Dimethyl sulfoxide). In this work, the successful application of pristine PC 61 BM as an annealing‐free ETL is reported for conventional PSCs, by ingeniously utilizing the “saturated solution” strategy. Specifically, the perovskite precursor solution is presaturated with PC 61 BM before deposition, in this way, not only the underlying PC 61 BM layer can be “reserved”, the added PC 61 BM in perovskite is also able to passivate defects in perovskite grain boundaries, thus facilitating charge transporting and reducing charge recombination. Encouragingly, the PC 61 BM ETL can avoid high‐temperature calcination or thermal annealing, thus greatly simplifying the manufacturing processes and reducing production costs. The CH 3 NH 3 PbI 3–x Cl x ‐based champion device shows the highest efficiency of 20.85% with high reproducibility. The strategy is simple, straightforward, and cost‐effective, when compared to most of the present reported ways for depositing ETLs.