Analysis of the light trapping effect on the performance of silicon-based solar cells: absorption enhancement

Nowadays, there is a great interest in discovering alternative approaches to reduce the cost per the output power of first generation crystalline silicon solar cells. Light propagation in solar cells is controlled by interaction between periodic structure filters and light. Therefore, designing ultrathin solar cells in which light is trapped in the active layer is so important to efficiently absorb the light. In the present paper, the combination of a distributed Bragg reflector (DBR) with a rectangular- or triangular-shaped grating is introduced as a photonic backside filter for both TE and TM polarizations. It is shown that by applying this DBR with a triangular grating, it is possible to enhance the efficiency of crystalline solar cells up to 20% for 2.5 [mu]m Si cells in TE-polarized incident light. By optimizing the shape of the grating, the efficiencies can be increased to 22.1% and 23.52% in 5 [mu]m and 7.5 [mu]m Si solar cells for TE-polarized incident light, respectively. Similar results have been achieved for TM-polarized incident light. In addition, introducing rectangular or triangular grating structures improves light trapping over the solar spectrum from 400 to 1100 nm which is revealed by calculation of the electric field. The triangular-shaped gratings are an effective approach for light trapping in thin crystalline solar cells and will inspire low-cost high-efficiency solar cell designs. Finally, efficiency as a function of angle of incidence of light for a triangular grating has been obtained. Finding results in this work show promise for designing ultrathin solar cells with enhanced light absorption.