Efficient green-solvent, additive-free and post-treatment-free organic solar cells enabled by dithiazolobenzotriazole-based polymer donors

• • PTzEH-F achieves 19.17% PCE as-cast from toluene without additives or post-treatments, demonstrating a viable route to eco-friendly processing while maintaining high efficiency. • • The ternary LbL device (PTzEH-F/L8-BO:PC71BM) reaches 20.27% PCE, indicating that DTzBT-based donors can be integrated into advanced device architectures for further gains. • • PTzMe-F, with N-methyl side chains, yields only 2.64% PCE (chloroform) due to poor solubility and miscibility with L8-BO, underscoring the critical role of side-chain engineering in morphology control. • • DTzBT building block lowers HOMO levels via thiazole fusion, enabling higher VOC while maintaining aggregation tunability, as evidenced by the improved performance of PTzEH-F over PTzMe-F.