Enhanced device performance of organic solar cells via reduction of the crystallinity in the donor polymer

Abstract

A new π-conjugated polymer, poly(2,5-dioctyloxyphenylene vinylene-alt-3,3-dioctylquater thiophene) (PPVQT-C8), consisting of alternating p-divinylene phenylene and 3,3-dialkylquater thiophene units, was synthesized for use in organic solar cell devices. The crystallinity of poly(quaterthiophenes) (PQTs) was reduced by introducing p-divinylene phenylene units between pairs of quaterthiophene units. A well-mixed nanoscale morphology of PPVQT-C8:PCBM photoactive layer resulted from this modification, which increased the power conversion efficiency relative to devices based on highly crystalline PQTs. Bulk heterojunction solar cells based on PPVQT-C8:PC60BM blends with a 1 : 3 ratio presented the best photovoltaic performances, with a short-circuit current density (Jsc) of 6.7 mA cm−2, an open-circuit voltage (Voc) of 0.67 V, a fill factor (FF) of 0.62 and a power conversion efficiency (PCE) of 2.8% under illumination of AM 1.5 with light intensity of 100 mW cm−2. The charge carrier mobility and morphology studies indicated that an optimized interpenetration network composed of PPVQT-C8: PCBM could be achieved in a blend ratio of 1 : 3.