A cathode interlayer based on an indandione-terminated quinoidal compound enables 19% efficiency in binary organic solar cells

Abstract

Cathode interlayers (CILs) are critical components in organic solar cells (OSCs), yet high-performance CILs remain predominantly reliant on aromatic units. Herein, we rationally design and synthesize a CIL (Q6P) based on an indandione-terminated quinoidal structure. The molecular structure of Q6P was unambiguously confirmed through single-crystal X-ray diffraction and supported by density functional theory (DFT) calculations. Incorporating phosphonate side chains not only enhanced the solubility of Q6P in polar solvents but also imparted self-doping characteristics, with the self-doping mechanism verified experimentally. Additionally, the quinoidal framework and low-lying LUMO energy level synergistically improved the self-doping level of Q6P. Q6P also demonstrated good charge transport and efficient charge extraction. When integrated into OSCs, the Q6P-based devices achieved a power conversion efficiency (PCE) of over 19%.