Solvent-Assisted Low-Temperature Crystallization of SnO2 Electron-Transfer Layer for High-Efficiency Planar Perovskite Solar Cells

A high-quality polycrystalline SnO2 electron-transfer layer is synthesized through an in situ, low-temperature, and unique butanol-water solvent assisted process. By choosing a mixture of butanol and water as a solvent, the crystallinity is enhanced and the crystallization temperature is lowered to 130 degrees C, making the process fully compatible with flexible plastic substrates. The best solar cells fabricated using these layers achieve an efficiency of 20.52% (average 19.02%) which is among the best in the class of planar n-i-p-type perovskite (MAPbI(3)) solar cells. The strongly reduced crystallization temperature of the materials allows their use on a flexible substrate, with a resulting device efficiency of 18%.