Strategic Halogen Substitution to Enable High-Performance Small-Molecule-Based Tandem Solar Cell with over 15% Efficiency

摘要

Small molecules have been recently highlighted as active materials owing to their facile synthesisis method, well-defined molecular structure, and highly reproducible performance. In particular, optimizing bulk heterojunction (BHJ) morphologies is important to achieving high performance in solution-processable small molecule solar cells (SM-SCs). Herein, a series of benzodithiophene-based active materials with different halogen atoms substituted at the end-group, are reported, as well as how these halogen atoms affect the morphology of BHJ architectures through microstructure analyses. Materials with chlorine atoms show a well-mixed morphology and interpenetrating networks when blended with [6,6]-phenyl-C-71-butyric acid methyl ester, facilitating effective charge transportation. This controlled morphology helps attain excellent performance with a power conversion efficiency (PCE) of 10.5% and a highest fill factor of 78.0% without additives. In addition, it can be applied to two-terminal (2T)-tandem solar cells, attaining an outstanding PCE of up to 15.1% with complementary absorption in the field of the 2T-tandem solar cells introducing the SM-SCs. These results suggest that tailoring interactions with halogen atoms is an effective way to control BHJ architectures, thereby achieving remarkable performance in SM-SCs.