On the role of interface states in MOS solar cells

The various ways in which the interface states can affect the operation of the MOS solar cell has been discussed. Interface states affect the oxide voltage and the silicon band bending and cause an excess diode current to flow by recombination tunneling via interface states. It has been shown that the open-circuit voltage of an MOS solar cell is determined by the zero-voltage silicon band bending φoi, the oxide tunneling transmission factor at open circuit TocT, and the change in the oxide voltage between short and open circuit δVox. The dependence of Voc on the oxide thickness tox is therefore dictated by the change in the above three parameters with increasing tox. The most advantageous situation is that in which the interface-state density Nis as well as the product Nistox decrease with increasing oxide thickness. Experimental data obtained so far indicate that this is what happens in reality if the oxide is grown under suitable conditions, and the decrease in state density accounts partially for the increase in Voc with tox.