Improved Mechanical Adhesion Enabled by Bilayer Hole Transport Layers in Perovskite Solar Cells

We investigate buried-interface mechanical integrity in metal-halide perovskite half-cells using carbazole-based self-assembled monolayers (SAMs) and bilayer hole transport layers composed of metal oxide underlayers and SAMs. Combining macroscopic and microscopic characterization, we quantify interfacial fracture energy ( G c ​) and identify delamination pathways. SAM deposition on NiO x increases G c by approximately 10-fold compared with ITO, highlighting the importance of oxide underlayer selection. To isolate the effect of removing noncovalently bonded SAM molecules, we use vapor-deposited perovskite as a solvent-free model system, decoupling the rinse step inherent to solution processing. Removing loosely bound SAM molecules increases G c from 0.94 ± 0.08 J·m –2 to 4.82 ± 0.79 J·m –2 . These results show that oxide selection and SAM binding quality are both critical for strengthening buried interfaces and designing mechanically robust perovskite solar cells.