Improving device performance of perovskite solar cells by micro–nanoscale composite mesoporous TiO2

In perovskite solar cells, the morphology of the porous TiO2 electron transport layer (ETL) largely determines the quality of the perovskites. Here, we chose micro-scale TiO2 (0.2 µm) and compared it with the conventional nanoscale TiO2 (20 nm) in relation to the crystallinity of perovskites. The results show that the micro-scale TiO2 is favorable for increasing the grain size of the perovskites and enhancing the light scattering. However, the oversized TiO2 results in an uneven surface. The evenness of the perovskites can be improved by nanoscale TiO2, while the crystallinity and compactness are not as good as those of the films based on micro-scale TiO2. To combine the advantages of both micro-scale and nanoscale TiO2, by mixing 0.2 µm/20 nm TiO2 with a ratio of as the composite ETL, the device average power conversion efficiency was increased to 11.2% from 9.9% in the case of only 20 nm TiO2.