Efficiency optimizastion in intermediate band solar cells

The last generation photovoltaic devices aim to tackle the losses associated with the non absorption of below band gap photons and the thermalisation of above band gap photons to the band edges. In this thesis, numerical analysis were carried out on the new intermediate band solar cell (IBSC) that absorbs the sub-band gap photons through the intermediate band (IB) inserted inside the base region of n+-i-p+ structure. IB increases the photocurrent of the IBSC without decreasing the output voltage. The operation performance of IBSC has been investigated by two different mathematical models that are the detailed balance model (DBM) and the quasi-drift-diffusion model (QDDM), respectively.Maximum efficiency was obtained as 63,2% for EG=1,95 eV and 54,8% for EG=1,12 eV, under ideal conditions, when DBM has been applied. The effect of overlap on the performance of IBSC has been analyzed in detail. It was seen that the efficiency was decreased sharply when the overlap existed between absorption coefficients. The losses due to the thermalisation of the above band gap photons to the band edge, have also been reduced by carrier multiplication via Auger generation. Four types of IBSC including the Auger mechanism have been investigated and the maximum efficiency obtained was about 70% at nearly the band gap of silicon.The effects of mobility, effective density of states and non-linearity term due to high concentration of sun light on the efficiency of IBSC have also been studied using QDDM. The efficiency has been reduced at lower mobility values of excess carriers, at lower density of states and higher sun concentration including non linearity term. When the effective density of states was reduced from 1019 cm-3? to 1017 cm-3 in QDDM, not only the efficiency of IBSC has been reduced but also the optimum IB and the optimum base width has been changed. When the new optimum IB and the optimum base width values were used, the efficiency was improved by amount of 15%.Finally, the effect of internal electric field due to the non uniform generation of the electrons and the holes in the base region has been investigated using QDDM. It was concluded that, this internal electric field would not affect the efficiency of IBSC when the IB could be kept half filled through the base layer.