Improved surface hydrophobicity of self-assembled transport layers enables perovskite/silicon tandem solar cells with efficiency approaching 31%

[4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) self-assembled monolayer (SAM) as the hole transport materials have been demonstrated remarkable potential in perovskite solar cells (PSCs). However, the hydrophobicity of Me-4PACz presents a critical challenge for the fabrication of high-quality perovskite films due to its poor wettability. Here, a doped Al 2 O 3 with Me-4PACz to modify the Me-4PACz surface was proposed. On one hand, this approach improved the wettability of the Me-4PACz film, enhancing the coverage, uniformity, and buried interface properties of the perovskite film. On the other hand, compared to Al 2 O 3 modification alone, doping Al 2 O 3 with Me-4PACz allowed direct contact between the perovskite and Me-4PACz, resulting in better buried interface passivation. As a result, we achieved an efficiency of 22.71% for single-junction wide-bandgap perovskite solar cells (1.68 eV). Additionally, the efficiency of perovskite/silicon tandem solar cells was improved from 28.68% to 30.92%, with a significant reduction in hysteresis. Furthermore, the tandem cells demonstrated no degradation after 4200 s of operation at the maximum power point.