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.

Effects of Annealing Time on Triple Cation Perovskite Films and Their Solar Cells.

Cesium (Cs) contained triple-cation and mixed halide perovskite (CsFAMA) is broadly employed as light absorption layers for efficient and stable perovskite solar cells (PSCs) fabrication with high reproducibility. On the other hand, thermal annealing is a universal post-treatment method for perovskite films preparation. Moreover, thermal management highly depends on perovskite materials. However, no specialized study has been reported on CsFAMA perovskite to date. Herein, we have systematically investigated the influence of thermal annealing and annealing time on CsFAMA films and their solar cells. We demonstrated that heating time of 45 or 60 min at 100 °C is desirable. More interestingly, we found that the unannealed CsFAMA films exhibit ultrahigh photoluminescence (PL) intensities, much stronger than that of annealed films. Note that PL intensities gradually weaken as a function of annealing time. In particular, the PL intensities of fresh films (after antisolvent dripping) are at least 200 times higher than that of 60 min annealed films. To our knowledge, it is the first time to report this PL behavior. We speculate that it is due to quantum confinement effect of perovskite crystal nuclei and "cage effect" of DMSO intermediates in the fresh films. To this point, the unannealed CsFAMA films may have great potential in PL emission applications.