Role of Morphology and Förster Resonance Energy Transfer in Ternary Blend Organic Solar Cells

Organic solar cells (OSCs) fabricated from ternary blend thin film absorbers are designed to maximize the range of absorption in the solar spectrum and thus increase the short-circuit current density (JSC) of the device. Herein, we report OSCs formed with two different compositions of ternary blend thin films comprising two electron donors and one acceptor, namely, PTB7-Th/PCDTBT/IT4F and PTB7-Th/PBDB-T/IT4F. We evaluate the role of Förster resonance energy transfer (FRET) and blend morphology to achieve composition-dependent device performance. We observed ≥10% increment in JSC for both the ternary blends as compared to that for the PTB7-Th:IT4F binary blend, resulting in an enhanced power conversion efficiency (PCE) up to 10.34% for the PTB7-Th:PBDB-T:IT4F blend. We provide evidence that the two foremost parameters that control the PCE are blend morphology and FRET between donor components. The improved exciton generation rate for PCDTBT-based ternary blends was achieved, suggesting effective contribution of FRET toward enhanced device photocurrent, whereas the PBDB-T-based ternary blend excelled mainly due to suppressed carrier recombination as a result of favorable orientation with PTB7-Th/IT4F.