Efficient green-solvent, additive-free and post-treatment-free organic solar cells enabled by dithiazolobenzotriazole-based polymer donors
Developing organic solar cells (OSCs) processable from green solvents without additives or post-treatments is essential for sustainable manufacturing, yet high power conversion efficiency (PCE) remains difficult due to limited morphology control. Herein, we develop a new electron-deficient building block, dithiazolo[4',5':3,4;5'',4'':5,6]benzo[1,2-d][1,2,3]triazole (DTzBT), which fuses benzo[d][1,2,3]triazole (BTA) with thiazole to leverage S/N-mediated non-covalent interactions, enhance planarity and lower the HOMO. To isolate side-chain effects, two DTzBT-based donors, namely PTzMe-F (N-methyl) and PTzEH-F (N-2-ethylhexyl), have been designed and synthesized. PTzMe-F exhibits poor solubility and miscibility with L8-BO, yielding 2.64% PCE (chloroform). PTzEH-F exhibits excellent processability and favorable morphology, delivering 17.61% PCE (chloroform) and 19.17% as-cast from toluene without any additive or post-treatments. In addition, the ternary LbL device based on PTzEH-F/L8-BO:PC71BM achieved an impressive efficiency of 20.27%. Comprehensive characterization indicates that 2-ethylhexyl side chains afford optimal solubility while preserving strong intermolecular interactions and favorable phase separation. DTzBT mitigates BTA’s HOMO-raising tendency via electron-withdrawing thiazole fusion, reconciling aggregation tunability with energy-level control. These results show that precise backbone and side-chain co-design enables green-solvent, additive-free processing for high-performance OSCs, advancing sustainable photovoltaic manufacturing.