Modeling Down-Conversion and Down-Shifting for Photovoltaic Applications

The efficiency improvements achieved by adding idealized, top-mounted, down-conversion (DC) and luminescent down-shifting (LDS) layers to a commercial grade silicon solar cell are studied. A comparison is then made to silicon nanocrystals (Si-NC) LDS layer coupled to a silicon solar cell, where the optical properties of the Si-NC are based on measured data. Since the modeled DC and LDS layers are electrically isolated from the solar cell, the devices are studied by modifying the incident AM1.5G spectrum according to the bandgap, absorption and emission profiles, and global efficiency of the DC and LDS layers. Simulation results indicate that a minimum DC/LDS efficiency of 1 % is required to enhance the solar cell efficiency, and that this threshold rises to 38% for a Si-NC based LDS layer. Additionally, the incorporation of an optimal, perfectly efficient DC layer (200%) is shown to enhance the photovoltaic efficiency from 14.1 % to 16.6%as opposed to 16.3% for a perfect LDS layer (100%).