A Heterodimer Strategy toward Enhancing Solar Spectrum Absorption and Elevating the Triplet Energy Level of Singlet Fission Materials

Singlet exciton fission (SF) holds great potential in third-generation solar cell devices. Two major challenges in the design of SF materials are improving the triplet energy level and achieving broad-spectrum light absorption. Here, we demonstrate that heterodimer engineering, utilizing a conjugated high-energy-absorbing antenna coupled with a low-energy-absorbing SF material, provides an effective strategy to simultaneously capture high-energy photons and elevate the triplet energy level. A heterodimer (TP) comprising an energy-harvesting antenna, perylenediimide (PDI), and a singlet fission chromophore, terrylenediimide (TDI), was used in this study. Upon photoexcitation of the TP thin film at 490 nm, the excited state with PDI singlet character undergoes ultrafast energy relaxation to the TDI chromophore, subsequently achieving efficient singlet fission (SF) with a time constant of τSF = 8.7 ± 0.4 ps and a triplet yield of 189%. Both sensitized experiments and calculated energetics consistently confirm that the triplet energy level exceeds 0.98 eV. The ability to tune the triplet energy and absorption range of SF chromophores through heterodimer engineering provides a method to design new SF materials.