Hybrid Interface Engineering With Piperidinium Ionic Polymers Toward 21% Efficiency of Organic Solar Cells

The cathode interlayer (CIL) serves as a critical interfacial component that governs the performance of organic solar cells (OSCs) by directly modulating electrode conductivity, interfacial dipole, and work function. However, the widespread use of perylene-diimide-based CILs is constrained by their intrinsic limitations in finite conductivity and poor thickness tolerance. To address this issue, we propose a hybridization strategy by incorporating a piperidinium ionic polymer (PIP) into PDINN. The bulkiness of the ionization piperidinium group modulates the film-formation kinetics of hybrid CIL and endows additional electrostatic forces to promote tighter molecular packing of PDINN. Furthermore, the strong interfacial dipole introduced by piperidinium ionization collectively contributes to optimized film morphology, reduced cathode work function, and increased conductivity, resulting in superior CIL thickness insensitivity and markedly enhanced OSC performance. Notably, employing the PDINN:PIP hybrid CIL in PM6:D18:L8-BO-based devices yields a remarkable PCE of 20.85%, showing a pronounced improvement compared to the control device with individual PDINN as CIL (19.80%). This approach also demonstrated broad applicability, yielding excellent performance in multiple active-layer systems. Overall, this research underscores the effectiveness of piperidinium ionization on hybrid CILs to fully exploit their potential in OSCs.