Bimetallic Ag‒Au‒Ag nanorods used to enhance efficiency of polymer solar cells

Abstract

In this work, various sizes of bimetallic Ag–Au–Ag nanorods (NR), designated NR1, NR2, and NR3, were successfully synthesized and introduced into the hole-transporting layer (HTL, PEDOT:PSS) of polymer solar cells (PSCs) to enhance the power conversion efficiencies (PCEs) by taking advantage of the broadband cooperative plasmonic effect. With an increase in the length of Ag in the bimetallic NRs, a wider range of wavelengths, from the visible to the near-infrared region, could be absorbed. This was attributed to the transverse and longitudinal plasmon excitations of the NRs. As a result, P3HT:PC61BM-based PSCs with NR1 or NR2 embedded in the HTL showed a 9% and 10% enhancement in the PCE, respectively, relative to the reference device. Notably, NR3, with broad localized surface plasmon resonance excitations, showed a major improvement in the PCE of up to 18% with the same P3HT:PC61BM-based device structure. High-performance PSCs were achieved when NR3 was embedded into the HTL of PTB7:PC71BM-based PSCs. A device with the optimized doping content of 7 vol% NR3 can significantly enhance the short-circuit current density (Jsc) by 12%, and achieves an excellent level of performance with a PCE of 7.36%, accounting for a 19% enhancement contrast, relative to the control device. The origin of the performance improvement of PSCs with NRs was analyzed using TEM, SEM, and UV–Vis characterizations, along with theoretical simulations. It was found that the enhancement could be ascribed to the broad absorption region, appropriate doping concentration, and the scattering-induced absorption enhancement of the active layer. The findings herein successfully demonstrate a general and efficient approach toward the enhancement of the performance of PSCs by incorporating the Ag–Au–Ag NRs into the HTL, and indicate that an appropriate doping content and NR size can significantly influence Jsc and the fill factor.