Analysis of high-efficiency silicon solar cells

Performance data on high-efficiency concentrator (>18 percent at 25 suns) silicon solar cells are compared to results from an exact numerical model in which all parameters for the calculation are taken from the existing literature on bulk silicon. The numerical solution of the transport equations includes the effects of Fermi-Dirac statistics, bandgap narrowing, and Auger recombination. Cell performances as a function of sunlight concentration are predicted with reasonable accuracy using this model. Evidence for the existence of bandgap-narrowing effects is found by comparing experimental data to calculated values of spectral quantum efficiencies and open-circuit voltages under a variety of lifetime assumptions. The validity of using superposition with simple diode equations to approximate the behavior of silicon solar cells also is examined.