perovskite solar cells, titanium dioxide (TiO2), large area, stability, Materials of engineering and construction. Mechanics of materials, TA401-492, Chemical technology, TP1-1185

Titanium dioxide (TiO _2 ) 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 TiO _2 (mp-TiO _2 ) layer on fabricating large-area perovskite solar cells using TiO _2 as the electron transport layer, we have conducted a comprehensive study on the solution-processed PSCs with or without an additional mp-TiO _2 layer. Photoemission spectroscopy measurement indicates that, compared with the compact TiO _2 (cp-TiO _2 ) layers, the mp-TiO _2 layers possess a slightly larger work function, which will improve the electron extraction efficiency at the perovskite-TiO _2 interface. The PSCs with an additional mp-TiO _2 layer exhibit better performances than those with only a cp-TiO _2 layer. They suffer from a smaller efficiency loss when enlarging the device area from 0.16 to 1.44 cm ^2 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 cm ^2 . 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-TiO _2 layer for optimizing the performances of large-area PSCs using TiO _2 as the electron transport layer.