# Physical mechanisms contributing to nonlinear responsivity in silicon concentrator solar cells

#### Abstract

Comparison of experimental data with the results of present models indicates that silicon solar cell operation at high solar concentration is not completely understood. That silicon concentrator cells are not fully understood was first recognized as nonlinearities experimentally observed in the response of the short circuit current to increasing solar concentration. In order to interpret the experimentally observed sublinear responsivities, a review in the literature of the physical mechanisms which have significance for solar cell operation at high solar intensities is essential. These phenomena include bandgap narrowing, Auger recombination, carrier diffusion, and the loss of base conductivity modulation. In this thesis, through modeling with the Solar Cell Analysis Program in One and Two Dimensions, SCAP1D and SCAP2D, an extensive study of these phenomena on the steady-state performance of two major cell designs for silicon concentrator solar cells, the conventional design and the back-contacted design, is made. The back-contacted design includes both the interdigitated back contact (IBC) solar cell and the point contact concentrator (PCC) solar cell. Simulations with SCAP1D and SCAP2D of the sublinear responsivity have led to two important insights into the physical operation of silicon solar cells under high solar concentration: (1) in the case of high-resistivity base cells of conventional design, the loss of base conductivity modulation, coupled with a large source of recombination, has been identified as a cause of sublinear responsivity; and (2) in the case of the back-contacted cells, that is, the IBC and PCC cells, a self-consistent description of the cell performance has been found through the inclusion of the free carrier bandgap narrowing model by Abram et al., the reduction of the minority hole mobility in the base to approximately one-half (200 cm$\sp2$-V$\sp{-1}$-sec$\sp{-1}$) the majority hole value determined by Irwin, and the use of the ambipolar Auger coefficient of Dziewior and Schmid, 3.8 $\times$ 10$\sp{-31}$ cm$\sp6$-sec$\sp{-1}$.

#### Degree

Ph.D.

Gray, Purdue University.

#### Subject Area

Electrical engineering

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