Modulated aggregation on terpolymer towards 19.2 % green solvent processed binary organic solar cells

Abstract

Organic solar cells (OSCs) with efficiencies over 20 % demonstrate significant potential in the photovoltaic market. However, the fabrication of state-of-the-art OSCs often relies on the use of highly toxic solvents. To advance OSCs toward industrial production, it is crucial to develop efficient and environmentally friendly solvent-processed OSCs. In this contribution, 1,2,3-benzothiadiazole is used as a third monomer to modify the benchmark donor D18, affording three terpolymers: PiBTX (X = 10, 20, 30). Thanks to the steric hindrance introduced by 1,2,3-benzothiadiazole, the PiBTX terpolymers exhibit good solubility in the non-halogenated solvent o-xylene and high luminous efficiency. Moreover, the PiBTX terpolymers enable the modulation of multiple properties, including reduced HOMO energy levels, increased J-aggregation in both solution and film, and improved miscibility with the acceptor. Hence, the terpolymers PiBTX outperform D18 in o-xylene-processed OSCs. Notably, owing to efficient charge generation, transport, and extraction, leading to higher J_SC and FF, as well as the lower-lying HOMO energy level and potential Förster resonance energy transfer that reduce non-radiative recombination loss, the PiBT20 terpolymer achieves an impressive efficiency of 19.2 %, ranking among the highest for OSCs processed with green solvents. This work offers a robust strategy for designing efficient polymer donors that are compatible with green solvents.