Impact of fluorine substituted π-bridges on the photovoltaic performance of organic small-molecule donor materials

Two analogue molecules, BDTP-2F with difluorobenzene pi-bridges and BDTP-4F with tetrafluorobenzene pi-bridges, are designed to investigate the impact of fluorine substituted pi-bridges on photovoltaic performance. In comparison with BDTP-4F, BDTP-2F has a slightly red-shifted absorption spectrum but has a higher HOMO level, indicating that the increment of fluorine substitutions on the phenyl pi-bridge blue-shifts the absorption spectrum and down-shifts the HOMO level of small molecules. Particularly, much different photovoltaic performance is obtained when applying Y6 as an acceptor to blend with BDTP-2F and BDTP-4F as donors, respectively. The device based on BDTP-2F:Y6 yields a power-conversion efficiency (PCE) of 10.21%, while a much lower PCE of 5.76% is achieved for the BDTP-4F:Y6-based device, ascribing to the different morphological properties of the blend films. The results demonstrate that the engineering of fluorine substitutions on the pi-bridge is an effective strategy to manipulate the photovoltaic properties of small-molecule donor materials.

Automated summary

The study found that fluorine substitutions on the phenyl pi-bridge can affect the absorption spectrum and HOMO level of small molecules, ultimately impacting the photovoltaic performance. When blended with Y6, BDTP-2F shows a higher power-conversion efficiency compared to BDTP-4F.