Cu-Au Bimetallic Nanoparticles For Surface Plasmon Resanonce Enhancement In Organic Photovoltaic Devices

In recent years, a variety of plasmonic nanostructures have been developed and applied to fabricating plasmonic photovoltaic devices. Typically, plasmonic nanostructures such as noble metallic nanoparticles（NPs） can be incorporated into the interfacial layer or photoactive layer, enhancing the the light absorption of the photovoltaic devices. In addition, metallic NPs and nanostructures in the active layer can scatter incident light to produce longer propagation path. NPs with different size, shape, doping concentration have great plasmonic effect on light absorption of photovoltaic device.Gold NPs show good stability and typical localized surface plasmon resonance（LSPR）. Copper NPs that are cheaper relative to gold and silver have good electrical conductivity properties and wide LSPR in the visible range. Thus, copper NPs have been considered to have great application potential in optics and electronics. Nevertheless, copper NPs suffer from low stability due to their facile oxidation. To overcome this shortage, one of solutions is to wrap the copper NPs with gold shell. The core-shell Cu-Au NPs are expected to be more stable than copper NPs and less expensive than gold NPs. The as-prepared Cu-Au NPs were characterized using X-ray diffraction（XRD）, scanning electron microscope（SEM）, transmission electron microscope（TEM）, energy dispersive spectroscopy（EDS） and ultraviolet-visible（UV-vis） spectroscopy. The core-shell structure of the Cu-Au NPs has been verified. Cu-Au NPs exhibits a broad absorption band with the maximum at long wavelengths of 650-700 nm.The plasmonic photovoltaic device has been fabricated by incorporating Cu-Au NPs into the PEDOT:PSS layer. The NP-doped PEDOT:PSS layer was characterized using atomic force microscope（AFM）, transmittance spectroscopy, UV-visible absorption spectroscopy. The plasmonic effect of the NPs and the morphyology of NP-doped PEDOT:PSS layer have been clearly demonstrated. The J-V test revealed that PCE of the P3HT:PC₆₁BM device with 0.88 wt% Cu-Au NPs was improve by 13.4%（from 3.20 % to 3.63 %）, and Jsc improved by 32 %（from 8.24 mA?cm-2 to 10.91 mA?cm-2）. As for PTB7-Th-based devices, similar improvements in PCE and Jsc were also observed. The average PCE of PTB7-Th:PC₆₁BM devices increased from 6.51 % to 7.13 %, corresponding to an improvement of 9.5 %. The PCE of PTB7-Th:PC71BM devices increased from 7.53 % to 8.48 %, yielding an improvement of 12.6 %.