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 form better surface coverage for enhancing 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 through thermal evaporation or spin-coating for fabricating PSCs. The CbzNaphPPA-based SAMUL was chosen for fabricating inverted PSCs due to its highest crystallinity and hole mobility derived from the ordered H-aggregation, which resulted in a remarkably high fill factor of 86.45%. This 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.