Geometrically Asymmetric Phosphonium Zwitterions Enable Efficient Printable Mesoscopic Perovskite Solar Cells
Jianhang Qi, Yaxin He, Jiale Liu, Yongming Ma, Bolun Zhang, Dang Xu, Kai Chen, Yang Zhou, Anyi Mei, Hin‐Lap Yip, Zhong'an Li, Hongwei HanABSTRACT
Carbon‐based, fully printable hole‐transport‐layer‐free mesoscopic perovskite solar cells (p‐MPSCs) offer a low‐cost, scalable photovoltaic technology, yet suffer from efficiency losses due to non‐radiative recombination at electron‐selective interface. Here, we design geometrically asymmetric zwitterions, featuring a bulky charge‐dispersed triphenylphosphonium cation and a small charge‐concentrated sulfonate anion linked by an alkyl chain, to weaken intermolecular and intramolecular charge attraction, thereby constructing a permanent dipole interlayer that mitigates such recombination. By extending the alkyl spacer and introducing methyl substituents on triphenylphosphonium, the optimized zwitterion, 4‐(tri‐p‐tolylphosphonio)butane‐1‐sulfonate (4MePS), achieves an ultrahigh dipole moment of 14.92 Debye. 4MePS strongly interacts with both perovskite and TiO 2 to form surface dipoles, drastically lowering their work functions by 0.42 and 0.54 eV, respectively. Comprehensive characterizations confirm that 4MePS suppresses non‐radiative recombination and accelerates charge extraction in p‐MPSCs. Consequently, 4MePS‐treated p‐MPSCs deliver a champion power conversion efficiency (PCE) of 23.3% (vs. 21.8% for control) and a minimodule efficiency of 20.2% over 57.3 cm 2 , among the highest reported for p‐MPSCs. Encapsulated devices retain 90% of their initial PCE after 1200 hours of maximum power point tracking under 1‑sun illumination at 55 ± 5 °C. This work establishes a charge density‐asymmetric molecular design strategy for engineering interfacial dipoles toward high‐performance perovskite devices.