Rational design and engineering of Y-series small molecule acceptors for high-performance organic solar cells

The molecular engineering of small molecule-based acceptors (SMAs) is essential for developing high-performance organic solar cells (OSCs). Specifically, these SMAs need to have suitable band alignment, low energy band gaps, robust electron mobility, as well as excellent solubility and processability. In this study, we present two rational design strategies for a series of six SMAs (Y11M1-Y11M6) derived from the Y11 molecule. These SMAs utilize a benzotriazole-dithieno-pyrrole-based core, donor, acceptor, and bifunctional acceptor units. The results indicate that engineered SMAs exhibit more negative LUMO levels (−3.90 eV to −3.69 eV ), smaller band gaps (1.22 eV to 1.47 eV ), superior solubility, and high electron hopping rate and electron mobility compared to the reference Y11. Moreover, these materials demonstrate the optimal light-harvesting efficiency, broader infrared absorption, and lower binding energies, leading to improved short-circuit current density and charge mobility in OSCs. The electronic excitation analyses reveal that Y11M1-Y11M6 SMAs facilitate charge flow, exciton dissociation, and charge separation while minimizing the recombination losses. This research promotes the design of SMAs and highlights their potential to advance OSCs for commercial solar applications.