Dual Plasmonic Effects for Performance Enhancement of PBDD4T-Based Organic Solar Cells

Limited light absorption constrains the power conversion efficiency of thin-film organic solar cells (OSCs). Plasmonic nanoparticles offer an effective strategy for enhancing light trapping without increasing absorber thickness. In this work, mixed cubic and ellipsoidal colloidal Cu nanoparticles (c-Cu NPs) were incorporated into the ZnO electron transport layer (ETL) of inverted PBDD4T:PC 71 BM-based OSCs at volume ratios of 0, 0.25, 0.5, and 1% to exploit their dual plasmonic response. An optimal loading of 0.5% c-Cu NPs increased the PCE from 5.05% in the pristine device to 9.11%, representing an improvement of over 80% through simultaneous enhancements in the open-circuit voltage, short-circuit current density, and fill factor. The external quantum efficiency was enhanced by more than 50%, which is attributed to the broadband localized surface plasmon resonance of mixed-shaped Cu nanoparticles, resulting from near-field enhancement and forward scattering effects. The overall performance improvement is ascribed to the synergistic enhancement of charge generation, carrier mobility, and charge collection. Furthermore, the reduced defect density and smoother morphology of the c-Cu NPs–embedded ZnO ETL facilitate more efficient charge transfer and collection in the devices.