Growth, characterization and thermodynamic modeling of absorber and transparent conducting oxides for copper indium diselenide based thin film solar cells

The absorber and transparent conducting oxides (TCO) layers are the most important in the CIS-based solar cell structure. This dissertation focuses on selected process development and fundamental issues in these two layers.; In hope of identification of low temperature route to CIS, the Cu-In-Se phase diagram was estimated using a sub-lattice model. The predicted Cu-In-Se phase diagram suggested a low temperature (∼210°C) liquid+alpha-CuInSe 2 two phase region. An alternative route to CuInSe2 formation that uses this low melting liquid to obtain grain growth was demonstrated using RTP on the stacked precursor structure Cu-Se/In-Se/Mo/glass. The influence of various ambient compositions on phase transformations after rapid thermal processing was determined. A 5.08% efficiency device with Voc = 0.296 V, Jsc = 34.65 mA/cm 2 and fill factor = 49.54% was produced by using the absorber that is obtained by RTP on the CuSe/InSe/Mo/Glass precursor under Se control in a PVD system. The correlation between the defects in the absorber to the device performance was analyzed by Deep-Level Transient Spectroscopy (DLTS). A midgap defect level attributed to CuIn was identified and is believed to contribute to the low Voc and fill factor.; For solar cell applications, it is desirable for the TCOs to have both high electrical conductivity and transparency. These two properties vary oppositely with F content. A method for estimating the solubility of F in all the binary oxides was developed and applied to fluorine-doped tin oxide (FTO) as a function of temperature and of the partial pressure of dopant precursor.; Sputter deposition and characterization of ZnO thin films for application as a transparent conducting electrode have been studied. The effects of processing conditions on film properties, evolution of structural and electrical properties, and the influence of ion damage on the thin film properties were investigated. A base pressure 2∼3 x 10-7 Torr, 5∼6 mTorr gas pressure and 200∼300 W were found to be the appropriate conditions for R.F. diode sputtering of ZnO:Al films. The lowest resistivity obtained was 2.7 x 10-3 O·cm with a transmittance above 85% and bandgap Eg about 3.35 eV at RF power 250 W, 5 mTorr Ar pressure, and 3 x 10-7 Torr base pressure.