Effects of intermediate plasmonic structures on the performance of ultra-thin-film tandem solar cells

Although solar cells can meet the increasing demand for energy of modern world, their usage is not as widespread as expected because of their high production cost and low efficiency. Thin-film and ultra-thin-film solar cells with single and multiple active layers are being investigated to reduce cost. Additionally, multiple active layers of different energy bandgaps are used in tandem in order to absorb the solar spectra more efficiently. However, the efficiency of ultra-thin-film tandem solar cells may suffer significantly mainly because of low photon absorption and current mismatch between active layers. In this work, we study the effects of intermediate plasmonic structures on the performance of ultra-thin-film tandem solar cells. We consider three structures| each with a top amorphous silicon layer and a bottom micro-crystalline silicon layer, and an intermediate plasmonic layer between them. The intermediate layer is either a metal layer with periodic holes or periodic metal strips or periodic metal nano-clusters. Using a finite difference time domain technique for incident AM 1.5 solar spectra, we show that these intermediate layers help to excite different plasmonic and photonic modes for different light polarizations, and thereby, increase the absorption of light significantly. We find that the short-circuit current density increases by ∼12%, ∼6%, and ∼9% when the intermediate plasmonic structure is a metal hole-array, strips, and nano-clusters, respectively, from that of a structure that does not have the intermediate plasmonic layer.