Analysis of Non-Conventional Front Contact Patterns Impact on Concentrator Solar Cells Performances Through a 2.5-D Distributed Electrical Model

A 2.5-D distributed circuit model for concentrator silicon solar cells has been developed in order to assess cell performance in the presence of particular top contact grid pattern geometries. Three kinds of front contact patterns have been considered: a conventional comb-like pattern, a square-like pattern and a fractal (auto-similar) one. Typical electrical parameters have been chosen for bulk resistivity, emitter resistivity, metal-semiconductor contact resistivity and metal resistivity. In this way an accurate assessment of ohmic losses can be carried out. Simulations have been performed by means of ORCAD PSPICE software. A 100 μm-wide, 5 μm-thick contact frame has been applied to the cell perimeter and the current was supposed to be extracted by four points, in correspondence of the mid points of the four sides of the cell. The simulations have been carried out under the assumption of a uniform irradiance distribution incident onto the cell surface (an arbitrary irradiance distribution however can be simulated) with a concentration factor of 50. For each of the three structures geometrical parameters such as finger width, finger spacing, total coverage and number of autosimilarity levels have been varied in order to achieve the optimal performance in terms of power delivered by the cell, for three different values of cell dimensions, 1 cm × 1 cm, 1.5 cm × 1.5 cm and 2 cm × 2 cm. Simulations results show that fractal contact grid pattern provides the best performance in all three cases and the power difference increases with increasing cell dimensions; for a 2 cm × 2 cm cell, difference between fractal and square patterns reaches 13%.