Optical analysis of light management for finger designs in CPV systems

Abstract

Concentrated photovoltaic (CPV) systems can achieve high energy conversion efficiencies due to their use of concentrating optics and highly efficient solar cells; however, power losses arising from the front surface reflection and metallization shading typically contribute a significant fraction to the total power loss for these devices. In flat silicon photovoltaic (PV) modules, the front-metal finger shape is often shaped to minimize shading losses. Finger shape is even more relevant for CPV cells where the current density and front metal shading are much higher. This study compares the optical performance of five light management finger designs in CPV systems with two different refractive homogenizers. The optical efficiency and loss analysis were determined using ray-tracing simulations. It is shown that shaped, light diverting metal fingers can improve the optical efficiency in CPV systems by up to 9.9% absolute compared to rectangular fingers, corresponding to an absolute cell efficiency increase of 3.0%. Although sharp edged triangular finger structures may be challenging to fabricate, significant optical gains can still be achieved with trapezoid or rounded cap finger shapes.