The theory of the Schottky barrier solar cell

Abstract

The theory of Schottky barrier solar cells has been investigated and the following contributions have been made. A model of Schottky barrier solar cells with an insulating layer is described, which takes into account more accurately than has been done so far, the dependence of the barrier height on the density of interfacial states (D S) and consequently the various potential drops in the cell. Also taken into account is the recombination traffic through the interfacial surface states. This effect is important at high values of DS when it lowers the predicted efficiency. Recombination in the transition and bulk regions is also considered, but this does not usually have a very marked effect. Numerical results are given for an Au - SiO2-n--type Si contact. (Chapter 2)The effect of different meteorological conditions on Schottky barrier solar cells has been investigated. Similar results to those for p-n junction cells have been obtained, namely that although the output power density is reduced, a much higher conversion efficiency is possible when the solar cell is illuminated with diffuse radiation. (Chapter 3)The removal of the usual assumptions regarding the quasi-Fermi levels and the depletion layer, has led us to a formalism which yields the variation with position of the quasi-Fermi levels and of the band edges. However, one interesting point is that, when the n-type S.B.S.C. is being illuminated under short circuit conditions, the reduction Vi in the potential developed across the interfacial layer is found to be negative, whereas with the device forward biased without illumination VV is always positive (or zero when the bias voltage equals zero). (Chapers15 & 6)Whilst retaining the important features of the more general formalism, the usual assumptions regarding the slopes of the quasi-Fermi levels and the potential drop across the bulk region were carefully reintroduced, thereby facilitating the construction of a simplified model of a p-type S.B.S.C. Allowance for the imperfect communication between the metal and the bands of the semiconductor, shows that recombination in the semiconductors bulk and transition regions can dominate for interfacial layer thicknesses 2 25. The results of the calculations made show that the J-V characteristics of the p-type S.B.S.C. are strongly controlled by the parameters of the interfacial layer, which in effect determine the extent of the recombination within the solar cell. The reduction VV in the potential developed across the interfacial layer when the device is illuminated, is found to be negative for short circuit conditions, and positive at the maximum power point. (Chapter 7)

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