Low-Temperature-Deposited TiO₂ Nanopillars for Efficient and Flexible Perovskite Solar Cells

Organometal halide perovskite solar cells (PSCs) are promisingly applied to flexible solar cells because of the high power conversion efficiency (PCE) and intrinsic softness of perovskite materials. In the most efficient PSCs, mesoporous TiO₂ generally functions as the electron transporting layer. However, the mesoporous TiO₂ is typically generated through high-temperature thermal annealing that is not suitable for producing flexible PSCs. In this work, TiO₂ nanopillar arrays are directly deposited on flexible substrates using glancing angle deposition at low substrate temperature. The TiO₂ nanopillars strongly adhere to the flexible substrates, improving light harvesting in the perovskite layers, facilitating electron extraction and transportation, and enhancing the mechanical flexibility of the PSCs. The flexible PSCs hybridized with the TiO₂ nanopillars show a PCE as high as 13.3% and excellent photovoltaic stability after 500 cycles of bending at a small radius of curvature.