Effect of electron-transport polymer addition to polymer/fullerene blend solar cells

We report on a study of the effect of device annealing on the performance of bulk heterojunction organic solar cells made from a ternary blend of poly(3-hexylthiophene) (P3HT), [6,6]-phenyl C61-butyric acid methyl ester (PCBM) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). Photovoltaic device characteristics before and after annealing were measured under air mass 1.5 simulated solar illumination (100 mW/cm2). Annealing times up to ∼15 min resulted in a sharp increase in short circuit current density and power conversion efficiency, with more gradual improvements upon further annealing. This performance improvement is attributed partly to enhanced optical absorption and partly to improved charge collection, which may result from enhanced charge carrier mobilities.