Preparation of Efficient Organic Solar Cells Based on Terpolymer Donors via a Monomer-Ratio Insensitive Side-Chain Hybridization Strategy

Creating new donor materials is crucial for further advancing organic solar cells. Random terpolymers have been adopted to overcome shortcomings of regular alternating donor–acceptor (D-A) polymers of which the performance is often susceptible to batch-to-batch variations. In general, the properties and performance of efficient D1-A-D2-A and D-A1-D-A2 terpolymers are sensitive to the D1/D2 or A1/A2 monomer ratios. Side-chain hybridization is a strategy to address this problem. Here, six D1-A-D2-A-type random terpolymers comprising D1 and D2 monomers with the same π-conjugated D unit but with different side chains were synthesized. The side chains, containing either fluorine or trialkylsilyl substituents were chosen to provide near-identical optoelectronic properties but provide a tool to create a better-optimized film morphology when blended with a non-fullerene acceptor. This strategy allows improving the device performance to over 18 %, higher than that obtained with the corresponding D1-A or D2-A bipolymers (around 17 %). Hence, side-chain hybridization is a promising strategy to design efficient D1-A-D2-A terpolymer donors that are insensitive to the D1/D2 monomer ratio, which is beneficial for the scaled-up synthesis of high-performance materials.