Improvement of Open Circuit Voltage of SnO 2–nSi Solar Cells

Abstract

Tunnel metal-insulator-semiconductor (MIS) SnO2–nSi solar cells were made by oxidizing (100) and (111) Si substrates at various oxidation temperatures and times, and by spray-depositing SnO2 to the surface. Open-circuit voltage V oc decreases with increasing oxidation temperature, and the cells made on (100) Si have higher V oc than those on (111) Si which were made under the same oxidation conditions. V oc is related to the n-factor and effective barrier height. The n-factor increases linearly with increase of the density of surface states D ss, while the effective barrier height decreases slowly with increase of D ss. For the improvement of V oc, it is effective to increase D ss. Experimental results support the theoretical prediction. When the oxidation temperature decreases, D ss increases, which results in an increase of the n-factor and V oc. The (100) solar cell has a higher V oc than the (111) cell because it has a higher D ss.