On July 21, 2022,Nature Energy published on line a research article titled“A universal close-space annealing strategy towards high-quality perovskite absorbers enabling efficient all-perovskite tandem solar cells”. The project was jointly developed by Professor Dewei Zhao, Solar Energy Institute, SCU, Professor Xiaofeng Li from Soochow University, and Dr. Fan Fu from Swiss Federal Institute of Materials Science and Technology (EMPA). Changlei Wang, Associate professor of Soochow University, is the first author of the paper. Prof. Dewei Zhao of Sichuan University, Prof. Xiaofeng Li of Soochow University and Dr. Fan Fu of EMPA of Switzerland are the corresponding authors of the paper. Sichuan University is the joint corresponding institution.

The broad bandgap tunability of organic–inorganic metal halide perovskites enables the fabrication of multi-junction all-perovskite tandem solar cells with ultra-high power conversion efficiencies (PCEs). Controllable crystallization plays a crucial role in the formation of high-quality perovskites. Here we report a universal close-space annealing strategy that increases grain size, enhances crystallinity and prolongs carrier lifetimes in low-bandgap (low-E_g) and wide-bandgap (wide-E_g) perovskite films. By placing the intermediate-phase perovskite films with their faces towards solvent-permeable covers during the annealing process, high-quality perovskite absorber layers are obtained with a slowed solvent releasing process, enabling fabrication of efficient single-junction perovskite solar cells (PVSCs) and all-perovskite tandem solar cells. As a result, the best PCEs of 21.51% and 18.58% for single-junction low-E_g and wide-E_g PVSCs are achieved and thus ensure the fabrication of 25.15% efficiency 4-terminal and 25.05% efficiency 2-terminal all-perovskite tandem solar cells.(abstract)

In this work, the collaborating team based on the existing all-perovskite stacked battery technology (Nat.Energy 2017, 2, 17018; Nat. Energy 2018, 3, 1093), developed a universal method for regulating the crystallization of perovskite films, which showed good results in improving the quality of perovskite films with different bandgaps. After Close Space Annealing (CSA), the crystal size of perovskite is significantly increased, the carrier lifetime is significantly increased, and the density of defect states is significantly decreased, which can effectively restrain non-radiative recombination and finally obtain high-efficient single-junction wide-band gap and narrow-band gap perovskite cells. The efficiency of all perovskite four - and two-end stacked solar cells is more than 25%. The maximum power output is still 90% of the original value, showing good working stability when the unpackaged stacked device works in an inert gas glove box for 450 hours.

The above research was supported by the National Key R&D Program, the National Natural Science Foundation of China, the Science and Technology Program of Sichuan Province, the Basic Research Funds of the Central Universities, and the Engineering Characteristic Team Project of Sichuan University.

Article link：https://www.nature.com/articles/s41560-022-01076-9