Enhanced light harvesting through Förster resonance energy transfer in polymer-small molecule ternary systemElectronic supplementary information (ESI) available: Additional details of materials, sample characterizations, sample analysis and device characterizations are provided. See DOI: 10.1039/c6tc04667c

We report a conceptually new approach for preparing a ternary blend of polymer/small molecule/metal oxide using plasma nanotechnology and realized it in the fabrication of a high-performance self-powered broadband photodetector. Here, we demonstrate the Förster resonance energy transfer (FRET) effect in a polymer-small molecule system with the incorporation of rubrene, a small molecule. The high absorption of rubrene in the visible region expands the spectral absorption and assists in developing nano-morphology for enhanced charge transport. The polymer absorbs in the UV region and non-radiatively transfers the absorbed energy to rubrene by FRET effect. The time-resolved photoluminescence study reveals efficient excitation energy transfer from the polymer to the small molecule occurring on a nanosecond timescale, thereby confirming the occurrence of FRET. We also demonstrate the synergistic effect of FRET and energy cascade dominated mechanisms when used in the ternary structure (polymer/small molecule/metal oxide) to realize high-performance broadband self-powered photodetector with a very low dark current of 32 pA cm −2 and a high photoconductive gain of 24.34 at zero bias. Conclusively, this configuration has the potential to be directly utilized in traditional multiple donor/acceptor systems with separate spectral responses to work synergistically, thereby allowing an enhancement in both light absorption and photocurrent generation. A conceptually new approach to fabricate a robust ternary structure is introduced for light harvesting devices. An interesting photophysical mechanism of the ternary blend in a real device is highlighted where FRET strongly contributes to the performance enhancement of the device.