Domain modulation and energetic disorder in ternary bulk-heterojunction organic solar cells

Abstract

The compatibility of the third component mixing into binary blends primarily decides the device performance in ternary organic solar cells (t-OSCs). We added a wide-bandgap PCDTBT polymer as a third component into PTB7-Th: PC 71 BM binary blend, which improves photoconversion efficiency (PCE) with efficient energy transfer, enhanced light absorption, and better morphology of the ternary blends. The enhanced PCE is attributed to the absorption improvement and non-radiative Förster resonance energy transfer (FRET) between PTB7-Th/PCDTBT polymers and the formation of a more fine bi-continuous interpenetrating network with a large donor/acceptor interfacial area with improved phase separation in the ternary system. Simultaneously, the addition of PCDTBT into PTB7-Th: PC 71 BM binary blend promotes the energetic disorder at the donor/acceptor interface in t-OSCs. This energetic disorder is studied in terms of Urbach energy and electroluminescence quantum efficiency. It was observed that the addition of PCDTBT into PTB7-Th: PC 71 BM affects the Urbach energy of PTB7-Th: PC 71 BM, which changes in bulk from 42 to 40.50 meV, and 42.70–50 meV for donor/acceptor interface. Interestingly, the energetic disorder at the donor/acceptor interface increases while the disorder in bulk decreases after the addition of PCDTBT polymer. Our results indicate that incorporating a wide-bandgap polymer as a third component is an appropriate way to design high-performance devices. • The addition of PCDTBT polymer into the matrix of PTB7-Th promotes the domain modulation with high J sc and FF , resulting in high PCE in ternary OSCs. • More bi-continuous interpenetrating donor/acceptor networks with improved phase separation in the ternary blend of PTB7-Th: PCDTBT: PC 71 BM. • Urbach energy and EL QE provide a better insight into the charge carrier's bulk and interfacial properties in ternary OSCs.