MIS solar cells: A review

The metal-thin film insulator-semiconductor (MIS) structure is currently receiving much attention in solar cell studies. Both theoretical and practical investigations indicate that this structure offers a means of overcoming the principal deficiency of Schottky barrier solar cells, namely low open-circuit photovoltage, while maintaining the attractive features that have led the metal-semiconductor junction to be considered as a possible alternative to the p-n junction for large-area, terrestrial, solar cell applications. The thin insulating layer allows control over not only the magnitude of the dark current flowing through the diode, but also the dominant type (majority or minority carrier) of this current. Desirably low values of dark current have been postulated for majority devices incorporating suitable charge-trapping centers, located either within the insulator or at the semiconductor-insulator interface, and for minority carrier devices employing suitable insulator thicknesses, metal work functions and semiconductor resistivities. Theories based on these models are reviewed in this paper and are further examined, for relevance to practical solar cells, in the light of experimental data from a variety of MIS solar cells employing Si and GaAs substrates.