Plasmonic effects of gold nanostructures in organic solar cells

Abstract

Gold (Au) nanospheres, nanorods and nanoprisms were synthesized using the seed-mediated growth method. The structural, optical, and morphological properties of Au nanostructures were explored. Transmission electron microscope (TEM) and scanning electron microscope (SEM) were used to identify the shape and size of Au nanostructures. The average diameters of Au nanospheres (AuNSs) and Au seeds were 6 and 4 nm, respectively. Au nanoprisms with average edge length of 68 nm and Au nanorods (AuNRs) with an average length of 70 and width of 40 nm (aspect ratio of 1.9) were obtained. In UV-Vis spectra, plasmon absorption peaks of these nanostructures were located in the range of 395 to 629 nm for Au seeds (with the smallest sizes) to AuNRs (with largest sizes). X-ray diffraction (XRD) confirmed the face-centered cubic crystalline structure of Au, while Raman showed strong vibrational modes. Additionally, the structural, optical, and morphological properties of Poly[N-9'-heptadecanyl-2,7-carbazole-alt- 5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]:[6,6]-Phenyl-C61-butyric acid methyl ester (PCDTBT: PC70BM) layers with AuNSs, AuNRs, and Au nanoprisms were characterized.UV-Vis spectra were obtained within the absorption range of 378 – 564 nm. PCDTBT: PC70BM with Au nanoprisms absorbed at high intensity in comparison to the other samples. SEM micrographs revealed compact morphology with pin-hole defects. XRD and Raman analysis showed no crystalline domains. The electron transport layer, titanium dioxide (TiO2) and hole transport layer, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) were spin-coated and characterized. PCDTBT: PC70BM based organic solar cells (OSCs) were fabricated with Au nanostructures were incorporated between the electron-hole transport layer and the active layer. Analysis of the electrical characteristics of the devices was done using current density voltage (J-V). Power conversion efficiency (PCE) for the pristine device was 2.04 %, while AuNSs with plasmonics achieved 1.19%. A month after fabrication, the PCE for pristine and plasmonic devices with AuNSs increased to 2.08 and 1.72%, respectively. When compared to the other plasmonic devices, the device with AuNSs performed the best.