Electrical transport mechanisms in amorphous silicon/crystalline silicon germanium heterojunction solar cell: impact of passivation layer in conversion efficiency

The dark current-voltage of the Au/n(+) (a-Si:H)/n(SiGe)/p(c-Si)/Ag heterojunction structure have been investigated in order to determinate the electrical conduction mechanisms. The forward current at different temperatures was found to be increased exponentially at low applied voltage (V <= 0.4V) indicating that the conduction mechanism of the diode was controlled by the thermionic emission mechanism. While, at bias voltages higher than 0.5 V, the results obtained show that the carriers conduction was described by the space charge limited current mechanism. The effect of front surface field (FSF) on the photovoltaic parameters of Au/n(+) (a-Si:H)/n(SiGe)/p(c-Si) heterojunction solar cell is studied. The experimental results obtained yielded to an improvement of about 50 mV for the open-circuit voltage, 1.1 mA cm(-2) for the short-circuit current density, and about 1% for the cell efficiency compared to the conventional cell i.e. without a-Si: H thin layer (FSF).