Long-range absorption enhancement in organic tandem thin-film solar cells containing silver nanoclusters

We investigate the optical properties of silver nanoparticles used in tandem ultrathin-film organic photovoltaic cells. Experimental results indicate that the enhancement of an incident optical field persists into an organic dielectric for distances of up to 10 nm from the center of an array of approximately 5-nm-diameter nanoparticles. Furthermore, this enhancement exists far from the resonant particle surface-plasmon excitation energy. We propose a model to explain this long-range enhancement and investigate the role that cluster spacing, shape, and an embedding dielectric medium with a complex dielectric constant play in determining plasmon enhancement. This effect is shown to increase the efficiency of tandem organic solar cells, and the implications for further solar cell efficiency improvements are discussed.