Improved Efficiency of Si MOS Solar Cell due to Surface States and Oxide Charges

The effects of interface states and fixed oxide charges on a MOS solar cell operation are theoretically analyzed and optimum design condition is deduced. In a p-MOS cell, negative fixed charges or acceptor type surface states with small hole capture cross section and large tunneling capture cross section are found to be effective to improve the efficiency due to the enhancement of the built-in voltage, while give negative effects in an n-MOS cell. However, efficiency improvement rate by surface states is also found to be rather smaller than that by fixed charges. The obtained maximum improvement factor as compared with the corresponding Schottky diode is 2.25 at the fixed surface charge density of 3×1012cm-2and the oxide thickness of 12 Å.