Towards large-area perovskite solar cells: the influence of compact and mesoporous TiO2 electron transport layers

Titanium dioxide (TiO2) is a widely used electron transport material in organic-inorganic hybrid perovskite solar cells (PSCs). In order to reveal the influence of an additional mesoporous TiO2 (mp-TiO2) layer on fabricating large-area perovskite solar cells using TiO2 as the electron transport layer, we have conducted a comprehensive study on the solution-processed PSCs with or without an additional mp-TiO2 layer. Photoemission spectroscopy measurement indicates that, compared with the compact TiO2 (cp-TiO2) layers, the mp-TiO2 layers possess a slightly larger work function, which will improve the electron extraction efficiency at the perovskite-TiO2 interface. The PSCs with an additional mp-TiO2 layer exhibit better performances than those with only a cp-TiO2 layer. They suffer from a smaller efficiency loss when enlarging the device area from 0.16 to 1.44 cm2 and exhibit a better long-term stability. About 89% of the initial efficiency is retained after keeping in dry air for 1000 h for the device with an active area of 1.44 cm2. For both cases, increasing the active device area is beneficial to long term stability, photoluminescence measurement indicates that this is result from the degradation of perovskite films starts at the margin of the cells. Our work implies the indispensable role of the additional mp-TiO2 layer for optimizing the performances of large-area PSCs using TiO2 as the electron transport layer.