Optimization of tin oxide-based electron transport layer for perovskite solar cells

The electron transport layer is the key material in perovskite solar cells (PSCs), and tin oxide (SnO₂) has been considered as an ideal electron transport material. The SnO₂ prepared by the low temperature sol-gel method suffers from low crystallinity and poor electron transport properties. In this paper, the crystallinity of SnO₂ was increased by adding water as solvent addictive to sol-gel precursor, which finally increased the efficiency of solar cells. SnO₂-based electron transport layer was prepared through a sol-gel method and the preparation conditions were optimized. It was found that adding proper amount of water as the solvent addictive to prepare SnO₂ sol-gel under 80 ℃ for 24 h benefits the hydrolysis of SnCl₂, enhancing the reaction and crystallinity of SnO₂. Finally, the SnO₂ film was prepared via spin-coating annealing method. With the increase of water, both the crystallinity and electron transport properties were enhanced. When 150 μL of water was added, the obtained SnO₂ layer was compact and smooth. The short-cut circuit current was 22.77 mA/cm^2, the open circuit voltage was 1.037 V, the filling factor was 0.492 and the photo-electron conversion efficiency was 11.617%. However, excessive water addictive leads to more defects in the prepared SnO₂ films and finally leads to the decrement of efficiency.