High efficiency thin film solar cells with enhanced optical absorption by excitons

Research Project Outline

Thin film structures are essential for achieving low cost solar cells. However, thinning the active regions of solar cells often reduces the optical absorption efficiency. Enhancement of optical absorption in thin films is therefore required to keep the bulk efficiency and also to improve the total efficiency of solar cells. In this project, we pursue the ways to enhance optical absorption in thin films and to develop high efficiency solar cells. Exciton absorption is one of the promising candidates, because it can be added to the normal band-to-band absorption. Semiconductors with high exciton binding energy such as ZnO, GaN and CdAlSe2 are important materials in the shorter wavelength regions. The semiconductors sensitive to the main part of the solar spectrum exhibit rather lower binding energies, but by constructing superlattice and/or quantum dot structures, the exciton absorption can be considerably enhanced even in these materials. These investigations are based on the high quality thin films and heterostructures with wide areas grown by MBE, MEE and magnetron sputtering.