Huagui Lai, Jingwei Zhu, Rui-Tung Kuo, Urs Aeberhard, Zhan‐Hong Lin, Nada Mrkyvkova, Jincheng Luo, Severin Siegrist, Philipp Wechsler, Chih‐Jen Shih, Peter Šiffalovič, Cong Chen, Ayodhya N. Tiwari, Tzu‐Ying Lin, Dewei Zhao, Fan Fu
Flexible all-perovskite tandem solar cells (TSCs) promise lightweight power for portable and aerospace uses, yet performance remains limited by interfacial losses in narrow-bandgap (NBG) sub-cells, particularly arising from poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). Here, we uncover a previously unrecognized vertical phase segregation in PEDOT:PSS films, with an insulating PSS-rich surface layer atop a conductive PEDOT-rich base. This architecture induces interfacial electric dipoles that hinder efficient hole extraction. We find that the inclusion of Triton X-100 disrupts this segregation by modulating polymer interactions, thereby suppressing surface dipole formation. NBG perovskite cells incorporating this modified interface exhibit enhanced performance and reproducibility. This strategy enables flexible TSCs with a power conversion efficiency (PCE) of 25.4% and a proof-of-concept flexible tandem solar mini-module reaches 19.7%, with theoretical modeling projecting module efficiencies exceeding 24%. These results provide key insights into PEDOT:PSS interfacial phenomena and elucidate design principles for optimizing interfaces for next-generation flexible perovskite tandems. The performance of flexible all-perovskite tandem solar cells remains limited by interfacial losses in narrow-bandgap subcells. Here, authors incorporate Triton X-100 to disrupt the vertical phase segregation in PEDOT:PSS films, achieving maximum cell and mini-module efficiencies of 25.4% and 19.7%.