Benzo[<i>b</i>]thiophene-Series Solid Additives for Improving the Morphology and Photovoltaic Performance of Organic Solar Cells

Morphology control of the active layer plays a crucial role in affecting the performance of organic solar cells (OSCs). Herein, three benzo[b]thiophene (BzT)-series compounds, namely BzT, 5-bromobenzo[b]thiophene (BzTB5), and 5-chlorobenzo[b]thiophene (BzTC5), were developed as volatile solid additives (VSAs) in OSCs. Theoretical calculations revealed that BzT-series VSAs have more negative electrostatic potential distributions and larger dipole moments than do thiophene[3,2-b]thiophene (TT)-series VSAs, leading to stronger interactions with Y6. These interactions promoted ordered molecular stacking, better improved the miscibility between PBDT-DTBT and Y6, and induced smoother surface, smaller phase separation, tighter lamellar and π–π stacking, and large crystal coherence length values. These characteristics promoted the exciton diffusion, charge separation, transport, and collection, leading to simultaneously enhanced fill factor and short-circuit current density. As a result, the power conversion efficiency (PCE) significantly increased by 23.3%. In addition, BzT increased the PCE of PM6:Y6-based OSCs from 14.2% to 16.1%, PM6:IT-4F-based OSCs from 11.9% to 12.5%, PM6:PYTT-based OSCs from 13.3% to 14.4%, and D18:Y6-based OSCs from 15.4% to 17.7%. The long-term storage stability of BzT-treated OSCs was also improved. BzTB5 and BzTC5 also exhibited effective PCE enhancements of about 8%. This work demonstrated the potential of BzT-series as universal VSAs in improving the morphology and photovoltaic properties of OSCs.