Enhanced power conversion efficiency in iridium complex-based terpolymers for polymer solar cells

By introducing various low concentrations of Iridium complexes to the famous donor polymer of PTB7-Th backbone, new heavy metal containing terpolymers have been demonstrated. When blended with PC71BM, an obvious increase of power conversion efficiency (PCE) is obtained in 1mol% Ir containing polymer for different photovoltaic devices either using Ca or PDIN as cathode interface layers. The impact of molecular weight on the photovoltaic performance has been particularly considered by using three batches of control polymer PTB7-Th to ensure a fair and more convincing comparison. At similar molecular weight conditions (M-n: similar to 60kgmol(-1), M-w: 100-110kgmol(-1)), the 1mol% Ir containing PTB7-ThIr1/PC71BM blends exhibits enhanced PCE to 9.19% compared with 7.92% of the control PTB7-Th. Through a combination of physical measurement, such as optoelectrical characterization, GIWAXS and pico-second time-resolved photoluminescence, the enhancement are contributed from comprehensive factors of higher hole mobility, less bimolecular recombination and more efficient slow process of charge separation. Polymer solar cells: low concentrations of Iridium complexes boost efficiencyOnly 1mol% of Ir complex can do the trick to greatly enhance the efficiency of PTB7-Th: fullerene polymer solar cell from 7.9 to 9.2%. A collaborative research led by Youtian Tao from Nanjing Tech University, China shows that the power conversion efficiency of PTB7-Th: fullerene polymer solar cell can be enhanced by conjugating extremely low ratio of heavy metal Ir complex via ancillary ligand. The conclusions have proved robust for PTB7-Th with different molecular weight, different Ir complex concentrations and different cathode interface materials such as calcium or PDIN. These results prove the importance of heavy metal complex for highly efficient photovoltaic devices and demonstrate a promising design approach toward more efficient photovoltaic polymer donor materials.