Theoretical studies of new iridium-based terpolymer donors for high-efficiency triplet-material-based organic photovoltaics: Incorporation of different iridium(III) complexes

Screening potential terpolymer donors for high-performance triplet-material-based organic photovoltaics (T-OPVs) has been a challenge. Herein, four terpolymer donors, with different bis-tridentate iridium(III) complexes incorporated into the backbone of PTB7Ir, were designed and investigated by DFT and TD-DFT methods. The results show that, for designed 1-4 molecules, the bis-tridentate architecture in iridium complexes contributes to the formation of the orbital transitions involving iridium atoms, and promotes the enhancement of spin-orbit coupling (SOC) in heavy metals. Based on the efficient exciton transformation channel from the lowest singlet (S1) state to the third triplet (T3) state, the designed 1-3 have smaller energy differences (Delta ES1-T3) and larger SOC matrix elements (< S1|HSOC|T3 & rang;) between S1 and T3, resulting in the faster intersystem crossing (ISC) and triplet exciton formation. Furthermore, 1-3/PC71BM heterojunctions with-Delta GCRT<-0.1 eV (-Delta GCRT refers to the driving force of triplet charge recombination) could exhibit suppressed triplet charge recombination (CRT) processes. The calculation results suggest that designed 1-3 systems can present enhanced inter-facial charge transfer and photovoltaic performance, and become promising candidates for iridium-based terpolymer donors in T-OPVs. This work will provide valuable guidance for the molecular design of T-OPV terpolymer donors.