Tuning the donor-acceptor strength of low-bandgap platinum-acetylide polymers for near-infrared photovoltaic applications

Two near-infrared (NIR) absorbing metallopolyynes of platinum (P1 and P2) functionalized with a weakly electron-donating fluorene unit and two strong electron acceptors (viz. benzo[1,2-c:4,5-câ]bis([1,2,5]thiadiazole) and [1,2,5]thiadiazolo[3,4-i]dibenzo[a,c]phenazine) were synthesized and applied for NIR photovoltaic applications. With these designed weak donor-strong acceptor electronic traits, these metallopolymers possess narrow bandgaps of 1.54 and 1.65 eV and a low HOMO level of about 5.50 eV, thus inducing a power conversion efficiency up to 1% for bulk heterojunction solar cells at the NIR wavelength. Two low-bandgap polyplatinynes (P1 and P2) consisting of weakly electron-donating fluorene and strongly electron-withdrawing heteroquinoids are reported, which induce a significant charge-transfer in the polymer main chain. They have respective optical bandgaps of 1.54 and 1.65eV, with more favorable HOMO levels for near-infrared photo-to-electrical energy generation. Bulk heterojunction photovoltaic devices showing power conversion efficiency of up to 1% have been demonstrated.