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.

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“…It is remarked that the boundary conditions of the typical optimization problem can be overcome by engineering the light path: By redirecting the light from the metal grid lines onto the active cell area, the effective shading can become much smaller than the actual metal coverage. 13,14 This has been demonstrated by cloaked contacts 15,16 or effectively transparent contacts 17 and prismatic covers. 18,19 However, these technologies are associated with a more complex process chain or additional optical components and often come with additional constraints such as requirements for narrow fingers or a low maximal finger height, which limit practical application.…”

“…It is remarked that the boundary conditions of the typical optimization problem can be overcome by engineering the light path: By redirecting the light from the metal grid lines onto the active cell area, the effective shading can become much smaller than the actual metal coverage 13,14 . This has been demonstrated by cloaked contacts 15,16 or effectively transparent contacts 17 and prismatic covers 18,19 .…”