Strategy of Enhancing Built‐in Field to Promote the Application of C‐TiO2/SnO2 Bilayer Electron Transport Layer in High‐Efficiency Perovskite Solar Cells (24.3%)

Combining two kinds of electron transport layer (ETL) which have complementary advantages into a bilayer structure to form a bilayer ETL is an effective way to transcend inherent limitations of single-layer ETL, which is very helpful in the development of perovskite solar cells (PSCs). In this work, a strategy is proposed to break constraints on the application of the staggered bilayer ETL in high-efficiency PSC, namely utilizing a built-in field to overcome the dilemma in ECBM making it possible to improve VOC and FF simultaneously by tuning the Fermi level of ETLs properly. According to the strategy, a bilayer ETL structure comprised of C-TiO2 and SnO2 layer and corresponding Li-doping process are developed, and the characterization results confirm the effectiveness of the strategy, making the potentials of the C-TiO2 (Li)/SnO2 bilayer ETL fully released for its application in high-efficiency PSCs: a VOC of 1.201 V for an ordinary triple-cation-perovskite-based PSC and a photoelectric conversion efficiency of 24.3% for a low-bandgap-perovskite-based PSC with high haze FTO superstrate are successfully achieved, indicating that the C-TiO2 (Li)/SnO2 bilayer ETL is a successful application paradigm of the proposed strategy and very promising in the application of high-efficiency PSCs.