The effects of chromatic aberration on the performance of GaInP/GaAs/Ge concentrator solar cells from Fresnel optics

Results are reported for the effects of chromatic aberration on the electrical performance of triple junction (3J), GalnP/GaAs/Ge concentrator solar cells for indoor measurements. A Fresnel lens was moved away from the solar cell such that the concentration level increased, and then decreased while the lens-to-cell distance continued to increase. From such movement, the FF exhibited a series of minima and maxima in the region where light is apparently focused as determined by the naked eye. These effects are due to chromatic aberrations that affect the FF, and to some extent, the subcell short circuit currents in the 3J stack. Aberrations can drive the 3J device in a top cell-or middle cell-limited mode, and make the top cell FF become more predominant than the middle cell FF, or vice versa with the 3J FF influenced more by either subcell FF. It is shown that the multijunction celt power output is also affected, and the gain in power depends on the size of the solar cell relative to the size of the beam waist, and the focal length of blue light relative to that of red light.

Introduction

The continuing development of triple junction (3J) GainP/GaAs/Ge concentrator solar cells is making this technology closer to maturity and commercialization. It is recognized as the solar cell technology that produces the most W/cm² at 500 suns than any other while progress in boosting the efficiency keep rising. Already there has been another record efficiency of 37.30/₀ at 175 suns that was recently reported, as there have been other reports, that are continuing to stream in₁ from field tests on their reliability [1]–[3]. Successful demonstration of 3J concentrators operating at 1000 suns under steady state illumination has been published [4], [5] as well. However, one area that needs fudher studying to increase solar cell performance is in the system optics of the module, that is, Fresnel optics. Some studies focusing on improving Fresnel lenses to increase multijunction cell performance have been documented for dual junction GalnAs/GaAs concentrator cells [6].