Recently 12% efficient indium tin oxide (ITO) on silicon solar cells have been reported. Experiments indicate the presence of a thin interfacial insulating layer. Thus, these devices appear to belong to a class of semiconductor-insulator-semiconductor (SIS) solar cells where one of the semiconductors is a degenerate wide-band-gap oxide. We have developed a theory in terms of minority-carrier tunnel current transport through the interfacial layer where one semiconductor is in a nonequilibrium mode. The wide-band-gap semiconductor serves to block band-to-band majority-carrier current and thus, in principle, give better device performance than with an MIS solar cell. The effects of interfacial layer thickness, substrate doping level, surface states and interface charge, temperature on the performance of SIS solar cells have been calculated. These indicate that real-world ITO on silicon cells should be able to achieve 20% efficiency under AMl illumination. Other combinations of semiconductors would yield even better performance.

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The behavior of ITO-SiOx-pSi tunneling solar cell (MIS type) under concentrated light illumination is analyzed theoretically. Conversion efficiency as high as 22.7% is predicted at 75×AM1 illumination. At still higher light concentration the efficiency drops mainly owing to the resistance of the SiOx layer. The numberical calculations show the important role of the interface states in the tunneling process, electrical charge storage, and carrier recombination. Large current flowing through the diode can induce significant quasi-Fermi level drop across the insulator layer and electric charge storage in the depletion region. The operation of the diode cannot be explained by the standard MIS theory of low current densities. Therefore a more general treatment is presented here.

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Using the results of I. Lundström and C. Swensson for the tunneling capture cross-section of deep traps, the authors present a theoretical approach for accurately evaluating the tunneling current assisted by deep traps in Schottky diodes