Characterization of CuInSe2 material and devices:: comparison of thermal and electrochemically prepared absorber layers

CuInSe(2)-based absorber layers for photovoltaic devices have been fabricated using two different scalable processes, electrodeposition and sputtering, both followed by thermal annealing. The structural properties of the absorber layers were studied by SEM, XRD and MiniSIMS. Sputtered absorber layers exhibit larger grain sizes than electrodeposited layers, but both types of film consist of randomly orientated crystallites. Electrodeposited layers appear to have a uniform composition with evidence of a MoSe(2) layer at the back contact, whilst sputtered layers show no evidence for a MoSe(2) layer. The external quantum efficiency spectrum of films and completed devices was measured, and the band gap and broadening parameters were obtained using electroreflectance spectroscopy. A device based on electrodeposited CuInSe(2) achieved an AM 1.5 efficiency of 6.6%, whilst a device based on sputtered CuInSe(2) had an efficiency of 8.3%. Impedance measurements were used to calculate doping densities of 2 x 10(16) and 4 x 1015 cm(-3) for the electrodeposited and sputtered devices, respectively.