Metal-organic framework nanocrystals enabled efficient and durable two-step perovskite photovoltaics

The complete conversion of PbI2 into high-grade perovskite material with less trap-state density and long-term durability still remains challenging for two-step perovskite photovoltaics. In this work, nanoscale UiO-66, as a classical Zr-MOFs with respectable stability and high specific surface area, has been innovatively introduced into the PbI2 layer to facilitate the conversion process by morphology tuning and also ultimately improve the durability of the resultant perovskite photovoltaic devices. The added UiO-66 has impressively changed the morphology of PbI2 film from a pristine compact one into a porous structure, providing better contact with organic salt during second-step deposition, consequently benefitting the thorough and uniform perovskite conversion process. Importantly, the addition of UiO-66 has effectively suppressed the halide vacancies formation due to the increased halide vacancy formation energy at the interface, as evidenced by density functional theory (DFT) calculation, leading to noticeably enhanced charge transport property and greatly improved optoelectronic property. Furthermore, the crystal orbital Hamilton population (COHP) calculation result directly proves that the incorporation of UiO-66 has enhanced the stability of perovskite materials by intensifying the bonding interaction of Pb-I bonds at the interface. Consequently, the UiO-66-assisted devices deliver a champion power conversion efficiency of 23.05% with noticeably improved stability, significantly outperforming the pristine devices. This work demonstrates the brightening potential of MOFs to assist the consequential manufacture of highly efficient and stable perovskite solar cells for upscaling process and deployment in the near future.