Zirconia Spacer: Preparation by Low Temperature Spray-coating and Application in Triple-layer Perovskite Solar Cells

Perovskite solar cells (PSCs) with structure of TiO2/ZrO2/carbon triple-layer are attractive recently because of their inexpensive raw materials, scalable fabrication process, and outstanding stability. But little progress has been made in the low temperature fabrication of TiO2/ZrO2/carbon triple-layer structured PSCs. A major reason is that it is rather difficult to construct the ZrO2 spacer layer at low temperature. Herein, we report a facile low-temperature spray-coating method to prepare effective ZrO2 spacer layer in TiO2/ZrO2/carbon triple-layer PSCs using urea to tune the porosity. After optimizing the amount of urea and the thickness of zirconia to 1100 nm, power conversion efficiencies (PCE) of 14.7% for a single cell and 10.8% for a module with 5 cells connected in series (5x0.9 cmx 2.5 cm) were achieved. Furthermore, the PSCs could be stable for 200 d at constant temperature (25 degrees C) and humidity (40%). With this spray coating method, the zirconia layer on flexible substrate can endure 50 times of bending without any cracking. Compared to the conventional screen-printing method of ZrO2 spacer layer, the spray-coating alternative developed in this work shows advantages of more convenient to process, preparation under lower temperature, and compatibility to flexible substrate.