Side-chain engineering is an important strategy in designing novel polymer semiconductor materials for high-efficient organic solar cells. The use of trialkylsilyl side chains can improve the photovoltaic efficiency by decreasing the energy of the HOMO of the polymer and improving its crystallinity and hole mobility. Compared to simple linear derivatives, α-branching in the alkyl groups of trialkylsilyl side chains causes strong aggregation and excessive phase separation in the photoactive layer, leading to poor device performance. β-Branching of the alkyl groups has not yet been used in trialkylsilyl side chains. Herein, we describe a new polymer (J77) with triisobutylsilyl side chains to investigate the effect of β-branching on the molecular aggregation, optical properties, energy levels, and photovoltaic properties. We find that compared to α-branching, β-branching of alkyl groups in trialkylsilyl side chains significantly reduces aggregation. This enables J77 to form blend morphologies in films that provide high-efficient solar cells in combination with different non-fullerene acceptors. Moreover β-branching of the alkyl groups in trialkylsilyl side chains lowers the HOMO energy level of J77 and increases the open-circuit voltage of J77-based solar cells without sacrificing short-circuit current density or fill factor.

侧链工程是设计用于高效有机太阳能电池的新型聚合物半导体材料的重要策略。三烷基甲硅烷基侧链的使用可以通过降低聚合物的HOMO能量并提高其结晶度和空穴迁移率来提高光伏效率。与简单的线性衍生物相比，三烷基甲硅烷基侧链的烷基中的α-支化会在光敏层中引起强烈的聚集和过度的相分离，从而导致较差的器件性能。烷基的β-支化尚未在三烷基甲硅烷基侧链中使用。本文中，我们描述了一种具有三异丁基甲硅烷基侧链的新型聚合物（J77），以研究β-支化对分子聚集，光学性质，能级和光伏性质的影响。我们发现，与三烷基甲硅烷基侧链中的烷基的α-支化相比，β-支化显着降低了聚集。这使J77能够在薄膜中形成混合形态，从而提供高效的太阳能电池以及不同的非富勒烯受体。而且，三烷基甲硅烷基侧链中的烷基的β-支化降低了J77的HOMO能级并增加了基于J77的太阳能电池的开路电压，而不会牺牲短路电流密度或填充因子。