Plasmonic rear reflectors for thin-film solar cells: design principles from electromagnetic modelling

The use of plasmonic structures to enhance light trapping in solar cells has recently been the focus of significant research, but these structures can be sensitive to various design parameters or require complicated fabrication processes. Nanosphere lithography can produce regular arrays of nanoscale features which could enhance absorption of light into thin films such as those used in novel solar cell designs. Finite-difference-time-domain simulations are used to model a variety of structures producible by this technique and compare them against the use of mirrors as rear reflectors. Through analysis of these simulations, sensitivity of device performance to parameters has been investigated. Variables considered include the feature size and array period, as well as metal and absorber materials selection and thickness. Improvements in idealized photocurrent density are calculated relative to the use of rear mirrors that are a standard for solar cells. The maximum simulated increase to photocurrent density was 3.58mA/cm² or 21.61% for a 2μm thick Si cell relative to the case where a silver mirror is used as a rear reflector. From this, an initial set of design principles for such structures are developed and some avenues for further investigation are identified.