Printable WO3 electron transporting layer for perovskite solar cells: Influence on device performance and stability

Abstract In this work the differences between two electron transporting materials used as n-type selective contacts for perovskite solar cells cells based on CH 3 NH 3 PbI 3-x Cl x are evaluated: the classical titanium dioxide (TiO 2 ) and tungsten oxide (WO 3 ) as a potential alternative. WO 3 presents the advantage of being printable and does not require high annealing temperature: allowing cheap, expendable and efficient solar cells. Although few reports have demonstrated the strong potentialities of WO 3 as efficient electron transporting layer for perovskite solar cells, we specifically focus our analysis on its influence on device stability. In this context, while solar cell performance under ambient conditions and continuous standard illumination is rapidly decreasing in the presence of WO 3 , we observe a drastic improvement of device stability in the dark under ambient conditions of WO 3 -based devices compared to TiO 2 . Exploiting Kelvin probe force microscopy (KPFM) the lower open-circuit voltage is explained, through transient photoluminescence measurements the crucial role played by oxygen vacancies and moisture is pointed out to rationalize this behavior. Finally, demonstrations of perovskite solar cells containing spincoated or printed WO 3 processed under ambient condition and presenting power conversion efficiency close to 10% are provided.