Characterisation of the GaAs-based intermediate band solar cell with multi-stacked InAs/InGaAs quantum dots

We report on both the photovoltaic and the optical properties of GaAs p-i-n solar cell (SC) and GaAs p-i-n SC with multiple InAs quantum dot (QD) layers in the i-region. Current-voltage and impedance spectroscopy measurements have been used to characterise the two SC devices. Refractive index, extinction and absorption coefficients were deduced from spectroscopic ellipsometry. I-V measurements in dark and illumination conditions have been carried out to investigate the photovoltaic effect in these devices. Our results suggested that the presence of trap states could cause the degraded photovoltaic performance of the QD SC device. The C-V characteristics of the QD SC device show forward bias region with negative values of capacitance, which is caused by the filling process of the dots near the junction. The equivalent circuit model consisting of two-series connected RC networks with a series resistance Rs was found to give a good fit to the experimental data.