Insulated Interlayer for Efficient, and Photostable Electron-Transport-Layer-Free Perovskite Solar Cells.

Currently, the most efficient perovskite solar cells (PSCs) mainly use planar and mesoporous titanium dioxide (TiO2) as an electron-transporting-layer (ETL). However, due to its intrinsic photocatalytic properties, TiO2 can decompose perovskite absorber and lead to poor stability under solar illumination (ultraviolet light). Herein, simplified architectural ETL-free PSC with enhanced efficiency and outstanding photostability is produced by the facile deposition of Bathocuproine (BCP) interlayer. Power conversion efficiency (PCE) of ETL-free PSC improves from 15.56% to 19.07% after inserting the BCP layer, which is the highest efficiency reported for perovskite solar cells involving ETL-free architecture, versus 19.03% for the n-i-p full device using TiO2 as ETL. The BCP interlayer has been demonstrated to be with several positive effects on the devices photovoltaic performances such as "modulation doping" of perovskite layer, surface modification of FTO work function, and enhancing the carrier charge efficiency between FTO and perovskite. Moreover, the BCP- based ETL-free devices exhibits outstanding photo stability: the unencapsulated BCP-based ETL-free PSCs sustain over 90% of their initial efficiencies after 1000 h storage in the air and maintain 92.2% after 450 h exposure to full solar irradiation (without UV filter), compared to only 14.1% in the n-i-p full cells under the same condition.