Enhanced photocurrent response in photocells made with platinum-poly-yne/C₆₀ blends by photoinduced electron transfer

We report photocurrent and photoluminescence measurements on blends of the organometallic polymer Pt-poly-yne and C₆₀. Due to efficient intersystem crossing, triplet excitons with a binding energy of at least 0.8 eV are created after photoexcitation of Pt-poly-yne. We find that electrons are transferred from Pt-poly-yne onto C₆₀ by efficient ionization of the triplet exciton. This process gives rise to a photocurrent quantum yield of up to 1-2% in photocells fabricated in a layer structure of indium-tin oxide (ITO)/Pt-poly-yne and 7 wt.% C₆₀/aluminium. Evidence for the ionization of the strongly bound triplet excitons is provided by studies of luminescence in the blends. There is only partial quenching of the singlet emission band, but complete quenching of the triplet emission band, and the lifetime of the triplet emission at room temperature is reduced from 2 to 0.1 μs upon addition of 7 wt.% C₆₀.