Revealing the Critical Role of the HOMO Alignment on Maximizing Current Extraction and Suppressing Energy Loss in Organic Solar Cells

• Published in: iScience Vol. 19; no. C; pp. 883 - 893
• Main Authors: Zhang, Jianyun, Liu, Wenrui, Zhang, Ming, Liu, Yanfeng, Zhou, Guanqing, Xu, Shengjie, Zhang, Fengling, Zhu, Haiming, Liu, Feng, Zhu, Xiaozhang
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 27.09.2019; Elsevier
• Subjects: Energy Storage; Materials Characterization; Science & Technology - Other Topics; SOLAR ENERGY; Solid State Physics; Solid State Physics; Materials Characterization; Energy Storage
• ISSN: 2589-0042; 2589-0042
• DOI: 10.1016/j.isci.2019.08.038

For state-of-the-art organic solar cells (OSCs) consisting of a large-bandgap polymer donor and a near-infrared (NIR) molecular acceptor, the control of the HOMO offset is the key to simultaneously achieve small energy loss (Eloss) and high photocurrent. However, the relationship between HOMO offsets and the efficiency for hole separation is quite elusive so far, which requires a comprehensive understanding on how small the driving force can effectively perform the charge separation while obtaining a high photovoltage to ensure high OSC performance. By designing a new family of ZITI-X NIR acceptors (X = S, C, N) with a high structural similarity and matching them with polymer donor J71 forming reduced HOMO offsets, we systematically investigated and established the relationship among the photovoltaic performance, energy loss, and hole-transfer kinetics. We achieved the highest PCEavgs of 14.05 ± 0.21% in a ternary system (J71:ZITI-C:ZITI-N) that best optimize the balance between driving force and energy loss. [Display omitted] •NIR acceptors with high structural similarity and variable HOMO levels were designed•We achieved the highest PCE of 14.36% by combining J71, ZITI-C, and ZITI-N acceptors•We revealed the importance of the optimized driving force on the device performance Energy Storage; Materials Characterization; Solid State Physics