Competing effects of field localization and absorption enhancement using plasmonic nanostructures in thin film a-Si solar cells

The, sometimes, competing effects of field localization at plasmonic resonances and the use of nanoplasmonic structures to enhance light absorption in thin film solar cells is discussed in this paper. Resonant nanoplasmonic structures are embedded in the front or back metal oxide layer of the solar cell for absorption enhancement. The intense field localization at plasmonic resonances leads to loss in the metal nanostructure itself and in the very near surrounding dielectric even if the dielectric is of low loss. A nanoplasmonic metal cross is used, as an example, to enhance the light absorption of the thin film silicon solar cell and a full wave analysis is performed to study the detailed field patterns. Although a broadband enhancement of the total light absorption is demonstrated, the practical enhancement needed in the semiconductor part of the solar cell is reduced due to absorption loss caused by field localization. and the improvement of solar cell performance is lower than expected. Methods to reduce field localization loss will be discussed in the presentation. A new plasmonic structure that exhibits broadband enhancement of light absorption with lower absorption loss due to field localization is proposed.