Perovskite solar cells (PSCs) have the advantages of low material cost , The advantages of easy fabrication of large area devices and high photoelectric conversion efficiency have attracted wide attention. SnO2 is widely used in n-i-p PSCs because of its high transmittance, high electron mobility, suitable energy level, good stability under UV irradiation and easy processing at low temperature. However, defects in the bulk and surface (oxygen vacancies (VO), dangling hydroxyl groups (-OH), and unsaturated coordinated metal atoms) easily cause carrier accumulation and nonradiative recombination loss. In addition, the insufficient coordination of metal, halogen and organic ions in perovskite can also cause interfacial chemical reactions, which deteriorates the efficiency and stability of the device. Therefore, the optimization of the buried interface of PSCs is the key to achieve its high efficiency and stability. However, due to the non-exposed nature of the buried interface, it is challenging to study and optimize it.
In view of this, Ji Xiaofei, an assistant researcher of Lu Linfeng's team at Shanghai Institute of Advanced Studies, developed a simple and effective strategy by adding formamidine oxalate (FOA) to SnO2 nanoparticles to suppress both the bulk and surface defects of SnO2 and the FA +/Pb2 + related defects at the perovskite buried interface. Ffective targeted defect passivation is achieved. The research results are based on "Target Therapy for Buried Interfacial Engineering Enables Stable Perovskite Solar Cells with 25.05%". Efficiency is published in Advanced Materials. It is
found that formamidine ions and oxalate ions are distributed in the SnO2 layer in a longitudinal gradient manner, and mainly gather at the SnO2/perovskite buried interface to regulate the crystal growth of perovskite, reduce the bulk phase and interface defects, and improve the energy level matching between perovskite and SnO2. The results showed that the energy conversion efficiency of PSCs increased from 22. 40% to 25. 05% after FOA treatment, and the storage stability and photostability of PSCs were also significantly improved. The schematic diagram
of FOA regulating perovskite crystal growth, improving interface energy level matching and reducing interface defects. This study provides an effective way for targeted treatment of buried interface defects and improving the performance of PSCs. The first authors of the paper are Ji Xiaofei, an assistant researcher at the Institute of Advanced Studies, and Bi Leyu, a doctoral student at City University of Hong Kong. The corresponding authors of the paper are Professor Guo Xugang of Southern University of Science and Technology, Professor Alex Jen and Dr. Fu Qiang of City University of Hong Kong. The research was supported by the National Natural Science Foundation of China, the Major Special Project of Basic and Applied Basic Research of Guangdong Province, Shenzhen Science and Technology Innovation Committee and Shanxi Science and Technology Department.
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