Anion–π interactions suppress phase impurities in FAPbI3 solar cells

• Published in: Nature (London) 2023-11, Vol.623 (7987), p.531-537
• Main Authors: Huang, Zijian, Bai, Yang, Huang, Xudan, Li, Jiatong, Wu, Yuetong, Chen, Yihua, Li, Kailin, Niu, Xiuxiu, Li, Nengxu, Liu, Guilin, Zhang, Yu, Zai, Huachao, Chen, Qi, Lei, Ting, Wang, Lifen, Zhou, Huanping
• Format: Article
• Language: English
• Subjects: 119/118; 140/131; 140/146; 639/301/299/946; 639/638/298; Anions; Chemical interactions; Commercialization; Energy conversion efficiency; Fourier transforms; Halides; Humanities and Social Sciences; Impurities; Intermediates; Iodine; Lead compounds; Maximum power; Metal halides; multidisciplinary; NMR; Nuclear magnetic resonance; Perovskites; Photovoltaic cells; Photovoltaics; Point defects; Purity; Reaction kinetics; Science; Science (multidisciplinary); Solar cells; Sunlight
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-023-06637-w

Achieving both high efficiency and long-term stability is the key to the commercialization of perovskite solar cells (PSCs) 1 , 2 . However, the diversity of perovskite (ABX 3 ) compositions and phases makes it challenging to fabricate high-quality films 3 – 5 . Perovskite formation relies on the reaction between AX and BX 2 , whereas most conventional methods for film-growth regulation are based solely on the interaction with the BX 2 component. Herein, we demonstrate an alternative approach to modulate reaction kinetics by anion–π interaction between AX and hexafluorobenzene (HFB). Notably, these two approaches are independent but work together to establish ‘dual-site regulation’, which achieves a delicate control over the reaction between AX and BX 2 without unwanted intermediates. The resultant formamidinium lead halides (FAPbI 3 ) films exhibit fewer defects, redshifted absorption and high phase purity without detectable nanoscale δ phase. Consequently, we achieved PSCs with power conversion efficiency (PCE) up to 26.07% for a 0.08-cm 2 device (25.8% certified) and 24.63% for a 1-cm 2 device. The device also kept 94% of its initial PCE after maximum power point (MPP) tracking for 1,258 h under full-spectrum AM 1.5 G sunlight at 50 ± 5 °C. This method expands the range of chemical interactions that occur in perovskite precursors by exploring anion–π interactions and highlights the importance of the AX component as a new and effective working site to improved photovoltaic devices with high quality and phase purity. The use of anion–π interactions during perovskite film formation is shown to give better quality perovskite layers with high phase purity, leading to improved photovoltaic devices with high power conversion efficiency.