The effects of high level injection on the performance of high intensity, high efficiency silicon solar cells

Abstract

With SCAP2D, a two-dimensional numerical code for silicon solar cells, we have explored the mechanisms controlling performance in high intensity high efficiency cells, focusing on the point contact cell for which record efficiencies have been reported. Our studies demonstrate that accurate Predictions of the intensity dependence of the short circuit current and open circuit voltage of these cells can be obtained by the inclusion of free carrier bandgap narrowing in the base and the reduction of the reported the Auger coefficient to be over four times the Dziewior and Schmid value [6-81. MODELING OF POINT CONTACT CELLSWe have examined with SCAP2D the steady-state short circuit current and open circuit voltage performance of two point contact cells reported by Sinton and Swanson, an 86 pm cell and a 240 pm cell [6,9]. minority carrier mobility in the base to approximately one-half the conventional value of Caughy and Thomas. In addition, the value for the ambipolar Auger coefficient by Dziewior and Schmid is retained, despite recent measurements which suggest it may be a factor of four larger than this. Band gap narrowing due to high injection conditions in the base may be another important limiting factor in silicon solar cells.

Physical parameters of highly injected silicon in the modeling of concentrator solar cells

“…As mentioned in The middle curve shows the experimental data assuming the BGN model used in [5]. The Auger coefficient needed to fit this data is nearly twice as large as that assumed in [5], which is shown in the bottom curve. The large difference between the lower curves is much bigger than any experimental error.…”

“…We should also like to point out that while the plieiiomma of carrier induced bandgap narrowing is likely to play a role in high-resistivity solar cells, the specific iiiodel used in [5]. from [16], may be questionablc.…”

“…Aueer Recombination /BandeaD Narrowing Bandgap narrowing due to carrier injection is an entirely plausible physical phenomenon whose possible effects in solar cells had been overlooked before [5]. From a modeling point of view, the main effect of this phenomenon is an increase in the intrinsic carrier density, n;; there is also a reduction in the effective ambipolar diffusion constant [ll].…”

“…From a modeling point of view, the main effect of this phenomenon is an increase in the intrinsic carrier density, n;; there is also a reduction in the effective ambipolar diffusion constant [ll]. In [5] , using the same data, the choice was made to extrapolate the value of C, = 3.8 x 10-31cmfi/sec [12] nieasured on heavily doped material ( N > 1 x liI"/cm3) to undoped highly injected material (n < 1 x 1017/cm3) and to modify n, accordingly.…”

“…Two significant changes have recently been proposed [5] as a. consequence of 2-D numerical modeling performed on high-resistivity point-contact concentrator solar cells. First, a sinaller than expected open-circuit voltage at high concentra.tions has been attributed in part to carrier-induced bandgap narrowing (BGN) rather than to Auger recombination exclusively.…”