Förster Resonance Energy Transfer Drives Higher Efficiency in Ternary Blend Organic Solar Cells

The use of a ternary blend is a promising strategy to enhance the power conversion efficiency of organic solar cells. However, an active layer thickness of ∼100 nm is typically required to achieve optimized performance in ternary blend organic solar cells. The efficiency of a thicker ternary blend film is limited by the low exciton diffusion length and charge carrier mobility of organic semiconductors, which leads to significant energy loss. In this work, we have employed a thick layer (∼300 nm) of ternary blend, featuring a donor–acceptor type diketopyrrolopyrrole (2DPP-BDT) based small molecule along with P3HT and PC71BM and established the role of Förster resonance energy transfer (FRET) to improve the power conversion efficiency (PCE). A dramatic enhancement (27%) in PCE was observed for the ternary blend organic solar cell compared to the binary blend solar cell containing P3HT:PC71BM as active layer. The performance enhancement is attributed to extended light absorption by the ternary blend photoactive layer, which emphasizes the contribution of 2DPP-BDT to harvest photons in the near-IR region of the solar spectrum. FRET between P3HT and 2DPP-BDT is found to be crucial in the exciton dissociation process. Steady state and transient absorption spectroscopy unambiguously established the role of FRET to enhance the device performance. This work highlights the significance of FRET to improve the performance of ternary blend organic solar cells.