High-efficiency ternary nonfullerene organic solar cells with record long-term thermal stability

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 8; no. 43; pp. 2297 - 22917
• Main Authors: Zhang, Cai'e, Ming, Shouli, Wu, Hongbo, Wang, Xiaodong, Huang, Hao, Xue, Wenyue, Xu, Xinjun, Tang, Zheng, Ma, Wei, Bo, Zhishan
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 21.11.2020
• Subjects: Charge transfer; Coherence length; Commercialization; Efficiency; Energy charge; Energy conversion efficiency; Energy transfer; Excitons; Interfaces; Miscibility; Morphology; Photoelectricity; Photovoltaic cells; Physics; Solar cells; Thermal stability
• DOI: 10.1039/d0ta07887e
• ISSN: 2050-7488

Achieving high-efficiency organic solar cells (OSCs) with long-term thermal stability is a major challenge toward commercialization. In the present study, a ternary blend strategy was employed to improve the thermal stability of OSCs with a novel small molecular acceptor ITC6-2F serving as the second acceptor. Compared with its parent compound ITC6-IC , the introduction of fluoro substituents at the two end groups can reduce the π-π stacking distance and enhance the intermolecular interactions in films. The PBDB-T : IDT-PDOT-C6 : ITC6-2F -based ternary blend film exhibits a reduced lamellar distance and an increased crystalline coherence length, compared to the corresponding binary blend films. Photo-physics and device physics analyses demonstrate that the charge-transfer state energy is dominated by PBDB-T and IDT-PDOT-C6 in the ternary OSCs. Also, ITC6-2F can facilitate the photonic energy transfer to IDT-PDOT-C6 and promote more excitons to reach the donor/acceptor (D/A) interfaces to achieve high-efficiency photoelectric conversion. More importantly, the enhanced intermolecular interactions and good miscibility between the two acceptors help to "freeze" the film morphology, leading to a significantly improved long-term thermal stability. The device efficiency remained at 80.3% of its initial value after 137 days of continuous heating at 75 °C in a nitrogen-filled glove box, which is a record result for high-efficiency OSCs reported so far. ITC6-2F as a third component in OSCs helps "freeze" the film morphology, leading to significantly improved long-term thermal stability.