Low Density of Gold Nanorods in the Anodic Layer for Enhancing the Efficiency of Organic Solar Cells

The effect of using an anodic layer with low density (similar to 6x10(8) cm(-2)) of gold nanorods (GNR) in organic bulk heterojunction poly(3-hexylthiophene) (P3HT) and phenyl-C-61-butyric acid methyl ester (PCBM) solar cells was studied. GNRs were deposited using several techniques, which produced various densities of GNRs on the anode layer. The anodic layers were characterized microscopically and spectroscopically. The power conversion efficiency and the short-circuit current for experimental devices incorporating GNR anodic layer showed an enhancement of up to 18% as compared to the control device. The results suggest that the electric field in the P3HT: PCBM active layer was increased by the localized surface plasmon resonances in GNRs. The increase in the electric field enhanced the photo-generation of excitons in the active layer near the plasmon peak, which improved the short-circuit current and the overall power conversion efficiency. Interestingly, photovoltaic devices with a low density of GNRs in the anodic layer showed an increase in the power conversion efficiency that was superior to that of devices with a higher density of GNRs in the anodic layer. This suggests that although the anodic layer with a higher density of GNRs absorbed more light, part of this light was confined in the anodic layer itself, and prevented from reaching the active layer of the bulk heterojunction device. In such cases, the power conversion efficiency was even found to be decreased with respect to the value for the control device.