Guo Jing, Hu Ke, Qiu Beibei, Zhang Jinyuan, Yang Dengchen, Zhou Liuyang, Li Shaman, Meng Lei, Zhang Zhanjun, Li Yongfang
School of Chemical Science, University of Chinese Academy of Sciences, Beijing 100049, China.
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
ACS Appl Mater Interfaces. 2021 Aug 4;13(30):36033-36043. doi: 10.1021/acsami.1c06830. Epub 2021 Jul 21.
Optimization of morphology and precise control of miscibility between donors and acceptors play an important role in improving the power conversion efficiencies (PCEs) of all-small-molecule organic solar cells (SM-OSCs). Besides device optimization, methods such as additives and thermal annealing are applied for finely tuning bulk-heterojunction morphology; strategies of molecular design are also the key to achieve efficient phase separation. Here, a series of A-D-A-type small-molecule donors (SM4, SM8, and SM12) based on benzodithiophene units were synthesized with different lengths of alkylthio side chains to regulate crystallinity, and their miscibility with the acceptor (BO-4Cl) was investigated. Consequently, SM4 with a short alkylthio substituent had a high crystallization propensity, leading to the oversized molecular domains and the poor morphology of the active layer. Meanwhile, SM12 with a longer alkylthio substituent showed weak crystallinity, causing a relatively looser π-π stacking and thus adversely affecting charge-carrier transport. The SM-OSC based on the small-molecule donor SM8 with a mid-length alkylthio substituent achieved a better PCE over 13%, which was attributed to a more harmonious blend miscibility without sacrificing carrier-charge transport. Eventually, the modulation of phase separation and miscibility via controlling the lateral side chains has proven its potential in optimizing the blend morphology to aid the development of highly efficient SM-OSCs.
优化形态以及精确控制给体和受体之间的混溶性在提高全小分子有机太阳能电池（SM-OSC）的功率转换效率（PCE）方面起着重要作用。除了器件优化外，还应用了添加剂和热退火等方法来微调本体异质结的形态；分子设计策略也是实现有效相分离的关键。在此，合成了一系列基于苯并二噻吩单元的A-D-A型小分子给体（SM4、SM8和SM12），其具有不同长度的烷硫基侧链以调节结晶度，并研究了它们与受体（BO-4Cl）的混溶性。结果，具有短烷硫基取代基的SM4具有较高的结晶倾向，导致活性层的分子域过大且形态不佳。同时，具有较长烷硫基取代基的SM12结晶度较弱，导致π-π堆积相对松散，从而对电荷载流子传输产生不利影响。基于具有中等长度烷硫基取代基的小分子给体SM8的SM-OSC实现了超过13%的更好的PCE，这归因于在不牺牲载流子电荷传输的情况下更和谐的共混混溶性。最终，通过控制侧链来调节相分离和混溶性已证明其在优化共混形态以助力高效SM-OSC发展方面的潜力。
