Room-Temperature Processing of TiO_x Electron Transporting Layer for Perovskite Solar Cells

In order to realize high-throughput roll-to-roll manufacturing of flexible perovskite solar cells, low-temperature processing of all device components must be realized. However, the most commonly used electron transporting layer in high-performance perovskite solar cells is based on TiO₂ thin films processed at high temperature (>450 °C). Here, we demonstrate room temperature solution processing of the TiO_x layer that performs as well as the high temperature TiO₂ layer in perovskite solar cells, as evidenced by a champion solar cell efficiency of 16.3%. Using optical spectroscopy, electrical measurements, and X-ray diffraction, we show that the room-temperature processed TiO_x is amorphous with organic residues, and yet its optical and electrical properties are on par with the high-temperature TiO₂. Flexible perovskite solar cells that employ a room-temperature TiO_x layer with a power conversion efficiency of 14.3% are demonstrated.