TiO 2 nanocrystal paste contains nanocrystals with narrow range of size which form a very uniform and transparent film of mesoporous TiO2. The paste can be applied as thick film by blade coating or screen printing for dye sensitized solar cells. For perovskite solar cells, the paste is first diluted and deposited as a thin film using spin coating. Thermal post-treatment is required after deposition. For thick films, a short ethanol vapor treatment helps level off the wet film. By thermal treatment, at around 100 °C the solvent is evaporated, at below 400 °C the binder is removed and at >500 °C nanocrystals are sintered into a sufficiently good conductivity film.