Harvesting solar energy using conjugated metallopolyyne donors containing electron-rich phenothiazine-oligothiophene moieties

A new family of soluble, solution-processable metallopolyynes of platinum(II) functionalized with electron-rich phenothiazine-oligothiophene rings and their corresponding dinuclear model complexes were synthesized and characterized. The organometallic polymers show different degrees of absorption capabilities in the solar spectral region, rendering some of them good electron donors for fabricating bulk heterojunction polymer solar cells by blending with a methanofullerene electron acceptor. The influence of the number of thienyl rings along the polymer chain on the optical and photovoltaic properties of these metallopolymers was studied. At the same donor:acceptor blend ratio of 1:4 or 1:5, the light-harvesting capability and solar cell efficiency notably increase as the number of thienyl rings is doubled. Photoexcitation of the polymer solar cells results in a photoinduced electron transfer from the π-conjugated metallopolyyne to [6,6]-phenyl C₆₁-butyric acid methyl ester and the best-performing polymer showed a power conversion efficiency (PCE) up to ∼1.3% with a corresponding peak external quantum efficiency of 63% under air mass (AM1.5) simulated solar illumination even at shorter absorption wavelength regime. The power dependencies of the solar cell parameters (including the short-circuit current density, open-circuit voltage, fill-factor and PCE) were also tested in detail.