Low-Temperature Photocrystallization of Atomic Layer Deposition-Processed Tin Oxide for Highly Efficient and Flexible Perovskite Solar Cells.

Atomic layer deposition (ALD) enables an excellent surface coverage and uniformity in the preparation of large-area metal-oxide thin films. In particular, ALD-processed SnO₂ has demonstrated great potential as an electron transport layer in flexible perovskite solar cells (PSCs) and tandem modules. However, the poor electrical conductivities and surface wettabilities of amorphous SnO₂ remain critical challenges for commercialization. In this study, a low-temperature and rapid crystallization process for amorphous SnO₂ is introduced, based on the use of high-power ultraviolet (UV) exposure (UV-SnO₂) to achieve high-performance flexible PSCs. The generation of highly dense O₃/OH radicals under UV exposure effectively ruptures the imperfect and weak bonds in the SnO₂ matrix, thereby facilitating the formation of nanocrystalline SnO₂. This transformation enhances the conductivity and shifts the energy levels upward, promoting electron injection and transfer from the perovskite. Rigid and flexible devices exhibit remarkable power conversion efficiencies (PCEs) of 22.86 and 21.49%, respectively. Furthermore, the flexible device demonstrates an excellent mechanical durability and environmental stability, retaining 93.3% of its initial PCE after 1500 bending cycles (r = 12 mm) and 87.4% after 1000 h under 1 sun illumination. These results highlight the potential of photocrystallization for advancing flexible PSC technologies.