Development of p(+), p, i, n, and n(+)-type CuInGaSe2 layers for applications in graded bandgap multilayer thin-film solar cells

Copper indium gallium diselenide layers with p(+), p, i, n, and n(+)-type electrical conduction, as predetermined, have been electrodeposited from aqueous solutions in a single bath. The photoelectrochemical cell has been used as the key analytical tool to determine the electrical conduction type, and X-ray fluorescence has been used to determine the stoichiometry of the corresponding layers. Optical absorption, X-ray diffraction, and atomic force microscopy have been used to investigate the bandgap, bulk structure, and surface morphology of the material layers, respectively. It has been found that the bandgaps of these layers can be varied in the range 1.10-2.20 eV. A four-layer n-n-i-p solar cell structure was fabricated and a corresponding energy band diagram for the device constructed. Current-voltage and capacitance-voltage measurements were carried out to assess the devices, and these parameters (V-oc approximate to 570 mV, J(sc)approximate to 36 mA cm(-2), and FF approximate to 0.40) indicate encouraging characteristics enabling further development of multilayer thin-film solar cells based on CuInGaSe2. The addition of a p(+) layer to the structure improved device parameters as expected due to improvements at the metal contact to the p(+) surface of the n-n-i-p-p(+) structure. (c) 2007 The Electrochemical Society.