10.1021/acs.nanolett.8b01440.s001 Xiu Gong Xiu Gong Qiang Sun Qiang Sun Shuangshuang Liu Shuangshuang Liu Peizhe Liao Peizhe Liao Yan Shen Yan Shen Carole Grätzel Carole Grätzel Shaik M. Zakeeruddin Shaik M. Zakeeruddin Michael Grätzel Michael Grätzel Mingkui Wang Mingkui Wang Highly Efficient Perovskite Solar Cells with Gradient Bilayer Electron Transport Materials American Chemical Society 2018 F doping level power conversion efficiency perovskite energy level alignment heterojunction PSCs SnO 2 ETL charge carrier transport device V OC F-doped SnO 2 bilayer ETL Gradient Bilayer Electron Transport Materials Electron transport layers SnO 2 nanocrystal AM 1.5 G illumination V OC Efficient Perovskite Solar Cells 2018-05-21 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Highly_Efficient_Perovskite_Solar_Cells_with_Gradient_Bilayer_Electron_Transport_Materials/6359720 Electron transport layers (ETLs) with suitable energy level alignment for facilitating charge carrier transport as well as electron extraction are essential for planar heterojunction perovskite solar cells (PSCs) to achieve high open-circuit voltage (<i>V</i><sub>OC</sub>) and short-circuit current. Herein we systematically investigate band offset between ETL and perovskite absorber by tuning F doping level in SnO<sub>2</sub> nanocrystal. We demonstrate that gradual substitution of F<sup>–</sup> into the SnO<sub>2</sub> ETL can effectively reduce the band offset and result in a substantial increase in device <i>V</i><sub>OC</sub>. Consequently, a power conversion efficiency of 20.2% with <i>V</i><sub>OC</sub> of 1.13 V can be achieved under AM 1.5 G illumination for planar heterojunction PSCs using F-doped SnO<sub>2</sub> bilayer ETL. Our finding provides a simple pathway to tailor ETL/perovskite band offset to increase built-in electric field of planar heterojunction PSCs for maximizing <i>V</i><sub>OC</sub> and charge collection simultaneously.