Broad-band plasmonic Cu-Au bimetallic nanoparticles for organic bulk heterojunction solar cells

• We prepared novel bimetallic Cu-Au NPs with core-shell nanostructures.
• The Cu-Au NPs exhibited broad-band LSPR absorption at wavelengths of 550–850 nm.
• The incorporation of Cu-Au NPs improved the light harvesting efficiency of OSC.
• The performance of Cu-Au NPs-embedding OSCs increased by up to 13.4%.

In this work, a facile preparation of Cu-Au bimetallic nanoparticles (NPs) with core-shell nanostructures is reported. Importantly, as-prepared Cu-Au NPs are highly stable, solution-processable and exhibit a broad localized surface plasmon resonance (LSPR) band at long wavelengths of 550–850 nm. Highly efficient plasmonic organic solar cells (OSCs) were fabricated by embedding Cu-Au NPs in an anodic poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer. The average power conversion efficiency (PCE) was enhanced from 3.21% to 3.63% for poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PC61BM) based devices, from 6.51% to 7.13% for poly[(ethylhexyl-thiophenyl)-benzodithiophene -(ethylhexyl)-thienothiophene](PTB7-th):PC61BM based devices and from 7.53% to 8.48% for PTB7-th:PC71BM based devices, corresponding to 9.5–13.4% PCE improvement. Such an improvement is very comparable to that (12.5%) obtained in those with plasmonic Au NPs but achieved at lower cost. This study thus demonstrates a novel and cost-effective approach to enhance the photovoltaic performance of OSCs, in combination with the broad-band plasmonic Cu-Au bimetallic nanostructures.

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