Highly efficient Ternary Solar Cells of 10.2% with Core/Shell Quantum Dots via FRET Effect

Ternary organic solar cells (OSCs) with the efficiency over 10% are fabricated as an inverted structure with core/shell type quantum dots (QDs) as third component. Forster resonance energy transfer occurs due to overlap between the emission range ((em)=500-800nm) of InP/ZnS QDs and the absorption range ((abs)=550-800nm) of PTB7-Th donor polymer. InP/ZnS QDs increase the photocurrent of the hybrid active layer via the strong emission properties of ZnS shells surrounding the InP core QDs, which transfer photon energy to PTB7-Th (UV-vis spectroscopy and photoluminescence). X-ray photoelectron spectroscopy (XPS) depth profiling reveals that InP/ZnS QDs are distributed on the surface of the hybrid active layer, while grazing-incidence wide-angle X-ray scattering (GIWAXS) analysis reveals that these QDs enhance the crystalline structure of the hybrid active layer. The incorporation of an ethanedithiol (EDT)-modified ZnO layer as an electron transport layer enhances the carrier transport and decreases carrier recombination, providing a uniform morphology and surface potential favorable for electron extraction and transport, as indicated by atomic force microscopy and electrostatic force microscopy analyses. Due to the synergistic effects of InP/ZnS QDs and the EDT-modified ZnO layer, the power conversion efficiency (PCE) is 10.2% via the enhancement in short-circuit current density (J(SC)) from 17.4 to 18.4mAcm(-2) and fill factor (FF) from 67.2 to 69.3%.