Shen Li, Lu Jitao, Liu Heyuan, Meng Qingguo, Li Xiyou
College of Chemical Engineering and Environmental Chemistry, Weifang University, Weifang 261061, China.
Institute of New Energy, China University of Petroleum (East China), Qingdao 266580, China.
J Phys Chem A. 2020 Jul 2;124(26):5331-5340. doi: 10.1021/acs.jpca.0c02248. Epub 2020 Jun 18.
Singlet fission (SF) is a spin-allowed carrier multiplication process that has potential to overcome the Shockley-Queisser limit of solar energy conversion efficiency for single-junction solar cells. It is of importance to prescreen appropriate SF candidates for both basic research and practical applications of SF. Besides common polycyclic aromatic hydrocarbons (PAHs), diketopyrrolopyrrole (DPP) derivatives also undergo efficient SF. A series of DPP derivatives with fused aromatic substituents were investigated considering their conjugation length, constitution, and the introduction of terminal substituents. A comparison of SF properties between nonfused and fused aromatic-substituted DPP derivatives was carried out. Detailed analysis focused on elucidating the relationship between the frontier molecular orbital energies, multiple diradical characters, and SF-relevant excited-state energy levels. Compared to nonfused aromatic-substituted DPP derivatives, fused aromatic-substituted DPP derivatives which contain three aromatic units (thiophene or furan) still share more appropriate energy levels for SF sensitizers. Changing the five-membered aromatic units with benzene ring and introducing -F, -OMe, and -COOH as terminal substituents are both effective ways to improve their performance as SF sensitizers. The results of this research help us to understand the SF properties of DPP derivatives deeply and are beneficial for the design of new DPP-based SF sensitizers.
单线态裂变（SF）是一种自旋允许的载流子倍增过程，它有潜力克服单结太阳能电池太阳能转换效率的肖克利-奎塞尔极限。为SF的基础研究和实际应用预先筛选合适的SF候选物很重要。除了常见的多环芳烃（PAHs）外，二酮吡咯并吡咯（DPP）衍生物也会发生高效的SF。考虑到其共轭长度、结构以及末端取代基的引入，对一系列具有稠合芳基取代基的DPP衍生物进行了研究。对非稠合和稠合芳基取代的DPP衍生物之间的SF性质进行了比较。详细分析集中在阐明前沿分子轨道能量、多重双自由基特征和与SF相关的激发态能级之间的关系。与非稠合芳基取代的DPP衍生物相比，含有三个芳基单元（噻吩或呋喃）的稠合芳基取代的DPP衍生物对于SF敏化剂仍具有更合适的能级。用苯环改变五元芳基单元并引入-F、-OMe和-COOH作为末端取代基都是提高其作为SF敏化剂性能的有效方法。本研究结果有助于我们深入了解DPP衍生物的SF性质，并有利于新型基于DPP的SF敏化剂的设计。
