Effects Of The Center Units Of Small-Molecule Donors On The Morphology, Photovoltaic Performance, And Device Stability Of All-Small-Molecule Organic Solar Cells

Rational design and synthesis of new small-molecule donors are critically important to achieve highly efficient small-molecule organic solar cells (SM-OSCs) with desirable device stability. Herein, two new acceptor-donor-acceptor (A-D-A) structured small-molecule donor materials SM-DTBDT and SM-BDT with dithieno[2,3-d:2 ',3 '-d ']benzo[1,2-b:4,5-b ']dithiophene (DTBDT) and benzodithiophene (BDT) as the core D-units are designed and synthesized, respectively. After thermal annealing treatment, the power conversion efficiencies (PCEs) of the SM-DTBDT- and SM-BDT-based devices with Y8 as acceptor material reach 12.45% and 10.68%, respectively. The main reason for the different device performance can be ascribed to the different crystallinity and morphology features of the small-molecule donor:Y8 blend films. Compared with the SM-BDT:Y8 blend films, the SM-DTBDT:Y8 blend films show a smoother surface, more uniform phase separation, mixed edge-on and face-on orientations, and enhanced crystallinity, resulting in the more efficient exciton dissociation and charge transport. In addition, it is observed that the SM-DTBDT-based devices also exhibit better stability. This work shows that fine-tuning the center units of small-molecule donors can not only increase the photovoltaic performance but can also be an effective method to improve the device stability.