Sidechain‐Engineered N‐PDIs Processed from Ethyl Acetate as Effective Cathode Interlayers for Organic Solar Cells

Herein, series bay position‐substituted N‐annulated perylene diimide (N‐PDI) derivatives applied as the cathode interlayer (CIL) in bottom‐anode (conventional structure) organic solar cells (OSCs) are presented. Despite the fact that N‐PDIs show low solubility in common CIL‐processing solvents such as methanol (MeOH), the use of ethyl acetate (EtOAc) as a processing solvent allows for dissolution of N‐PDIs at sufficient concentrations to form homogeneous films on top of the organic photoactive layer. OSC devices fabricated in ambient conditions using the PM6:Y6 representative bulk heterojunction (BHJ) system show simultaneous enhancements in performance metrics, with power conversion efficiency (PCE) increasing from 8.5% for devices based on the bare Ag cathode to 12.5% with N‐PDI molecule as CIL. The improvement in performance with N‐PDI CILs can be attributed to a combination of smooth film morphology and high electron extraction capability of N‐PDIs. Solubility in EtOAc, appropriate highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels, uniform film formation, and facilitation of electron transfer/collection make these N‐PDIs a promising family of CIL materials for efficient OSCs. Using EtOAc as an improved solvent over MeOH also opens the door for new CIL designs and to test materials that are not MeOH soluble.