Self-Promoted Vertical-Gradient Hole Transport Layers for Flexible Large-Area Perovskite Modules

While the power conversion efficiency (PCE) of single-junction perovskite solar cells (PSCs) has increased to over 26%, there are some challenges to achieving flexible large-area PSCs with good long-term stability for practical applications. In this work, we demonstrate a self-assembled gradient Ti₃C₂T_x MXene incorporated PEDOT:PSS HTL for promoting flexible large-area PSCs by establishing half-caramelization-based glucose-induced MXene redistribution. Through this process, the Ti₃C₂T_x MXene nanosheets are spontaneously dispersed and redistributed at the top region of HTL to form the unique gradient distribution structure composed of MXene:Glucose:PEDOT:PSS (MG-PEDOT). Our results show that the MG-PEDOT HTL not only offers favorable energy level alignment and efficient charge extraction, but also improves the film quality of the perovskite layer featuring enlarged grain size, lower trap density, and longer carrier lifetime. Consequently, the power conversion efficiency (PCE) of the flexible device based on MG-PEDOT HTL is increased by 36% compared to that of pristine PEDOT:PSS HTL. Meanwhile, the flexible perovskite solar minimodule (15 cm² area) using MG-PEDOT HTL achieves a PCE of 17.06%. The encapsulated modules show remarkable long-term storage stability at 85degC in ambient air (~90% efficiency retention after 1200 hours) and enhanced operational lifetime (~90% efficiency retention after 200 hours) [1]. With the adoption of the flexible transparent electrodes [2] and the introduction of a new modification on the perovskite active layer, the power-per-weight of our flexible PSCs reaches about 8 W/g while the power-per-weight of PEN/ITO-based control about 1-1.5 W/g. The work contributes to the development of flexible PSCs for practical applications.<br/>[1] R. Zhang, W.C.H. Choy, et al, Adv. Funct. Mater., 33, 2210063, 2023.<br/>[2] J. Kim, W.C.H. Choy, et al, Adv. Energy Mater., 10, 1903919, 2020.