Multiply Charged Conjugated Polyelectrolytes as a Multifunctional Interlayer for Efficient and Scalable Perovskite Solar Cells

Abstract A series of anionic conjugated polyelectrolytes (CPEs) is synthesized based on poly(fluorene‐co‐phenylene) by varying the side‐chain ionic density from two to six per repeat units (MPS2‐TMA, MPS4‐TMA, and MPS6‐TMA). The effect of MPS2, 4, 6‐TMA as interlayers on top of a hole‐extraction layer of poly(bis(4‐phenyl)‐2,4,6‐trimethylphenylamine (PTAA) is investigated in inverted perovskite solar cells (PeSCs). Owing to the improved wettability of perovskites on hydrophobic PTAA with the CPEs, the PeSCs with CPE interlayers demonstrate a significantly enhanced device performance, with negligible device‐to‐device dependence relative to the reference PeSC without CPEs. By increasing the ionic density in the MPS‐TMA interlayers, the wetting, interfacial defect passivation, and crystal growth of the perovskites are significantly improved without increasing the series resistance of the PeSCs. In particular, the open‐circuit voltage increases from 1.06 V for the PeSC with MPS2‐TMA to 1.11 V for the PeSC with MPS6‐TMA. The trap densities of the PeSCs with MPS2,4,6‐TMA are further analyzed using frequency‐dependent capacitance measurements. Finally, a large‐area (1 cm²) PeSC is successfully fabricated with MPS6‐TMA, showing a power conversion efficiency of 18.38% with negligible hysteresis and a stable power output under light soaking for 60 s.