Analysis of multi-crystalline silicon solar cells at low illumination levels using a modified two-diode model

Current-voltage characteristics of multi-crystalline silicon solar cells measured under several low illumination levels are analyzed. The fitting analysis is conducted using a modified two-diode equivalent circuit accounting for an additional ohmic series resistance in the vicinity of grain boundaries and allowing for variable diode ideality factors. Apart from the shunt resistance-a key factor at very low illumination levels-the model indicates two other current transport mechanisms at low illumination levels, both related to recombination, but each of them can be allocated to a different region in the cell: (1) recombination in the crystalline region and (2) recombination at grain boundaries. The role played by each mechanism is studied depending on illumination level. (C) 2010 Elsevier B.V. All rights reserved.