Light trapping in thin film plasmonic solar cells

Advanced light management in thin-film solar cells is becoming increasingly important to reduce semiconductor layer thicknesses (and thus costs) while still absorbing the full solar spectrum in the cell. Here, we discuss how the excitation of surface plasmon resonances in metal nanoparticles can serve to enhance the trapping of light in thin-film solar cells. We discuss three geometries, with particles either at the top or back of the cell, or embedded in the solar cell, and compare these different designs. We demonstrate the effectiveness of the plasmonic light trapping concept by presenting experimental data on ultra-thin n-i-p a-Si:H solar cells with plasmonic back reflectors. We show that using a properly designed scattering structure, the performance of cells on randomly textured Asahi substrates can be surpassed. The periodic patterns are made via an inexpensive and scalable nanoimprint method. Electromagnetic modeling is shown to agree well with measurements, and used to understand further details of the device.