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

• Published in: Advanced engineering materials 2023-05, Vol.25 (9), p.n/a
• Main Authors: Hoff, Anderson, Martell, Mark, Gasonoo, Akpeko, Koenig, Josh D. B., Simón Marqués, Pablo, Cieplechowicz, Edward, Pahlevani, Majid, Welch, Gregory Charles
• Format: Article
• Language: English
• Subjects: cathode interlayers; ethyl acetate; organic solar cells; perylene diimide
• ISSN: 1438-1656; 1527-2648
• DOI: 10.1002/adem.202201437

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. Nine N‐annulated perylene diimide molecules are presented and used as cathode interlayers in conventional‐type organic solar cell devices. Ethyl acetate is introduced as an effective interlayer processing solvent, compared with commonly used alcohols, that allows for better dissolution of the molecules and uniform film formation on top of the organic photoactive layer, leading to high‐performance devices.