Characterisation of monolithic tandem solar cells containing strain balanced quantum well sub-cells

Abstract

This thesis presents the milestone efficiency of 30.6% under 54x concentration achieved by a monolithic tandem solar cell containing strain balanced quantum well sub-cells. This is the first demonstration of tandem cells containing quantum well sub-cells. Characterisation and modelling of the quantum efficiency and dark currents of monolithic tandem cells containing quantum well sub-cells are also presented for the first time. Predictions performed by a simulation program indicate that 32.3% efficiency at 500x concentration can be achieved and in combination with an active Ge substrate efficiencies of 37.5% are possible. The model created in the simulation program is presented which makes possible the accurate fitting of quantum efficiency and prediction of dark current. The procedure developed to process tandem solar cells into concentrator devices is presented. A detailed account of the characterisation methods used for tandem solar cells are also described. Going further, a new optical concept for building integrated PV design was examined in this thesis. The design is based on a Buffon lens as an alternative to convex and Fresnel lens designs. The low cost design presented can be accommodated in the space of a double glazing window for glass facades.