Model calculations for metal-insulator-semiconductor solar cells

An analytical approach to calculating MIS solar cell properties has been formulated and utilized to study solar cell efficiency as a function of interfacial layer thickness, various interfacial film parameters and band gap. Three models are considered regarding interface state recombination kinetics. Calculations are presented for the case of interface states being in equilibrium with the metal (Model (I), in equilibrium with the majority carriers of the semiconductor (Model II) and in equilibrium with the minority carriers (Model III). It is found that in all three cases, the efficiency of low barrier height, Schottky barrier cells can be increased very significantly. For example, it is shown that for a band gap of 1.5 eV and a barrier height of 0.5 eV, it appears possible to increase the cell efficiency from essentially zero to 12%. If the barrier height is 1.0 eV, an efficiency of over 20% is possible. It is determined, however, that MIS solar cell performance is limited by leakage currents due to minority carrier diffusion back into the bulk. As a result, the upper limit of performance is defined by that for a homojunction. These calculations identify ranges of surface state density and interfacial barrier heights necessary for a good MIS solar cell.