Efficiency enhancement of ternary blend organic photovoltaic cells with molecular glasses as guest acceptors
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Previously reported glass-forming perylenediimide (PDI-glass) and diketopyrrolopyrrole (DPP-glass) acceptors were used as ternary components to modulate the morphology and electron transport properties of bulk heterojunctions composed of the polymer blend poly(3-hexythiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM). Both ternary acceptors show strong absorption in the visible range and energy levels intermediate between that of P3HT and PCBM. In the blends, both amorphous materials occupy the interface between P3HT and PCBM domains without significantly altering film morphology. The incorporation of 20% PDI-glass and 15% DPP-glass in ternary blend devices has resulted in conversion efficiency enhancements of 38% and 36%, respectively. Additionally, the incident photon to electron conversion efficiency of the ternary devices of these materials was increased with additional photocurrent between 660 and 750 nm, indicating that these materials efficiently contribute to light harvesting. This justifies the efficiency enhancements via the charge transfer mechanism. Furthermore, these ternary devices show high stability towards both moisture and oxygen.