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

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: PC₇₁BM 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: PC₇₁BM 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: PC₇₁BM affects the Urbach energy of PTB7-Th: PC₇₁BM, 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.