Spin‐coated and vacuum‐processed hole‐extracting self‐assembled multilayers with H‐aggregation for high‐performance inverted perovskite solar cells

Abstract We report a highly crystalline self‐assembled multilayer (SAMUL) that is fundamentally different from the conventional monolayer or disordered bilayer used for hole‐extraction in inverted perovskite solar cells (PSCs). The SAMUL can be easily formed on ITO substrate to establish better surface coverage to enhance the performance and stability of PSCs. A detailed structure‐property‐performance relationship of molecules used for SAMUL is established through a systematic study of their crystallinity, molecular packing, and hole‐transporting properties. These SAMULs are rationally optimized by varying their molecular structures and deposition methods through thermal evaporation or spin‐coating for fabricating PSCs. The CbzNaphPPA‐based SAMUL was chosen for fabricating inverted PSCs due to it exhibiting the highest crystallinity and hole mobility which is derived from the ordered H‐aggregation. This resulted in a remarkably high fill factor of 86.45 %, which enables a very impressive power conversion efficiency (PCE) of 26.07 % to be achieved along with excellent device stability (94 % of its initial PCE retained after continuous operation for 1200 h under 1‐sun irradiation at maximum power point at 65 °C). Additionally, a record‐high PCE of 23.50 % could be achieved by adopting a thermally evaporated SAMUL. This greatly simplifies and broadens the scope for SAM to be used for large‐area devices on diverse substrates.