Efficient ternary blend polymer solar cells with a bipolar diketopyrrolopyrrole small molecule as cascade material

Abstract

We present a ternary strategy to enhance the power conversion efficiency (PCE) of bulk heterojunction polymer solar cells (PSCs) with a bipolar small molecule as cascade material. A bipolar diketopyrrolopyrrole small molecule (F(DPP)2B2), as the second electron acceptor, was incorporated into poly(3-hexylthiophene) (P3HT): [6,6]-phenyl-C61-butyric-acidmethyl-ester (PC61BM) blend to fabricate ternary blend PSCs. The introduction of the bipolar compound F(DPP)2B2 can not only broaden the light absorption of the active layer because of its absorption in near infrared region but also play a bridging role between P3HT and PC61BM due to the cascaded energy level structure, thus improving the charge separation and transportation. The optimized ternary PSC with 5wt% F(DPP)2B2 content delivered a high PCE of 3.92% with a short-circuit current density (Jsc) of 9.63mAcm−2, an open-circuit voltage (Voc) of 0.62V and a fill factor (FF) of 64.90%, showing an 23% improvement of PCE as compared to the binary systems based on P3HT:PC61BM (3.18%) or P3HT:F(DPP)2B2 (3.17%). The results indicate that the ternary PSCs with a bipolar compound have the potential to surpass high-performance binary PSCs after carefully device optimization.