Reinforcing carrier transport via Interface hydrophilization for efficient inverted perovskite solar cells

Perovskite solar cells (PSCs) with a self-assembled monolayer (SAM) of the [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) as the hole transport layer (HTL) emerged as a promising photovoltaic technology due to its compatibility with low-temperature processing and exceptional stability. However, the high hydrophobicity and non-uniform distribution of the MeO-2PACz layer on the substrate significantly affect the charge carrier transport at the device interface and thus the photovoltaic performance of PSCs. Herein, a facile interface hydrophilization strategy of the SAM is reported by introducing the 4-hydroxybenzylphosphonic acid (4-HPA) into the MeO-2PACz to improve the hydrophilicity of the HTL for PSCs. The comprehensive results reveal that the 4-HPA applied as the hydrophilic additive in the HTL could facilitate MeO-2PACz cluster dispersion on the substrates, thereby enhancing the hydrophilicity of the HTL. Meanwhile, the 4-HPA-modified SAM exhibits superior energy level alignment with the perovskite to promote charge carrier transport at the device interface and thereby increase the charge carrier extraction of PSCs. Consequently, the PSCs based on the 4-HPA-modified HTL achieve a champion power conversion efficiency of 24.45 % with remarkable operation stability. This work provides a universal charge transport layer engineering for efficient PSCs, advancing the industrialization of high-performing PSCs.