Recombination saturation effects in silicon solar cells

Significant interest has recently been shown in the use of dark and illuminated current-voltage (I-V) measurements for the characterization of high-efficiency silicon solar cells. Similar nonideal behavior, in the form of “humps” in dark I-V curves, has been observed by various research groups but apparently different interpretations of this effect given. In this paper we present detailed computer simulations of solar cells with defects (producing recombination centers within the bandgap) at a number of specific positions in the devices. It is found that a distinct shoulder (or “hump”) occurs in the I-V characteristics when the recombination centers exhibit unequal electron and hole capture rates. Furthermore, it is shown that these shoulders are a result of the saturation of (Shockley-Read-Hall) recombination via the defect levels, which dominates behavior at low forward bias. As the bias voltage is increased, recombination in the defected region increases again, beyond the saturation level. The simulations show conclusively that the shoulders in the measured dark I-V curves of high-efficiency silicon solar cells produced at the University of New South Wales arise from the rear Si-SiO₂ interface