The effect of overlap between absorption coefficients on the variation of current densities in intermediate band solar cells

Intermediate band solar cell (IBSC) has a structure that absorbs the subbandgap photons by the help of the intermediate band (IB) located inside its base region and increases the photocurrent without decreasing the output voltage. In this study, detailed balance equations are used to investigate the current density (total, electron and hole currents) variations of IBSC with IB energy level, under nonoverlap and overlap conditions, in the cases of equal and nonequal absorption coefficients, for E_G=1.95 eV. It is obtained that in both cases; the IBSC has two optimum IB levels, one below half of the band gap and the other above half of the bandgap, under nonoverlap condition. The optimum IB levels shift towards the half of the bandgap under overlap condition in the case of equal absorption coefficients. If the new optimum IB levels are used, the current contribution of IB level becomes independent of overlap. But the current resulting from the transitions between valance band to conduction band decreases sharply from 26 mA/cm² to 8 mA/cm².when overlap increases from 0 to 4 eV. The reduction in this current is compensated in the case of nonequal absorption coefficients.