Laser Annealing of TiO2 Electron-Transporting Layer in Perovskite Solar Cells

Solution-processed TiO2 and other metal-oxide electron-transporting layers (ETLs) for perovskite solar cells commonly require high-temperature annealing (>450 °C), causing the underlying indium-tin oxide (ITO) to degrade and inhibiting the use of flexible plastic substrates, such as poly(ethylene naphthalate). Laser-based solar cell manufacturing is attracting increased interest and can enable rapid and low-temperature fabrication of perovskite solar cells. By using novel pulsed ultraviolet laser processing on the solution-processed TiO2, we demonstrate a champion 17.1% efficient flexible perovskite solar cell. We can independently control the annealing of the ETL without affecting the underlying ITO or substrate due to the shallow absorption depth and short pulse duration of the laser. Ellipsometry and X-ray photoelectron spectroscopy verify that the laser-annealed TiO2 thin film is stoichiometric and relatively denser than the thermally annealed control sample. The efficiencies of the laser-processed devices exceeded those fabricated via hot plate, but with the added benefit of a high-throughput, low-temperature, and flexible-substrate-friendly process.