| In Part 1 of this thesis minerals from the Cu-Bi-S and Cu-Sb-S phase systems are identified as candidates for use as the solar absorber in thin film PV devices. Thin films of the mineral wittichenite, Cu3BiS 3, were synthesized on fused silica substrates by heating Cu-Bi metal precursor films and Cu-S-Bi metal sulfide precursor films under H2S. The effect of precursor composition and structure, heating temperature, heating profile, and gas composition and pressure were systematically investigated. Phase-pure Cu3BiS3 films 250-1000 nm thick were synthesized, with the morphology of the films being dependent on the composition, structure, and heating profile of the precursor films. Regardless of processing conditions, Cu3BiS3 thin films produced in this two-step process are either discontinuous or contain hollow pockets between the film and substrate. The electrical resistivity of these Cu3BiS3 films ranged from 3-200 Ω·cm.; Cu3BiS3 thin films were also synthesized in a one-step process by reactive sputter deposition of Cu-S and Bi on heated fused silica substrates. Films produced by this process are crystalline, phase-pure, dense, smooth, and continuous. As-deposited films, 300-600 nm thick, have a direct forbidden band gap of 1.4 eV, an optical absorption coefficient of 1 x 105 cm-1 at 1.9 eV, p-type conductivity, and an electrical resistivity of 84 Ω·cm. The crystallite sizes of the films may be increased, and the electrical resistivity of the films decreased to 9.6 Ω·cm, by post-deposition annealing under H2S. Cu3BiS3 thin films of similar quality, 1.2 mum thick, were deposited on TCO coated soda-lime and borosilicate glass substrates by the same method. Material and method compatibilities were also investigated as a preliminary step in the application of combinatorial methods to the development of thin film PV devices based on Cu3BiS3.; In Part 2 of this thesis the effect of AC electrodeposition conditions on copper deposition into porous aluminum oxide templates are systematically investigated. A FFDOE was utilized to study the effect of five variables: frequency, voltage, pulsed or continuous deposition, electrolyte concentration, and barrier layer thinning voltage, on the quality of copper deposition into oxalic acid-anodized templates. Continuous AC sine wave deposition conditions yielded excellent uniformity of pore-filling, but damaged the PAO template when deposition was continued until bulk copper was deposited on the surface of the electrode. Pulsed electrodeposition yielded comparable uniformity of pore-filling and no damage to the PAO template.; Further optimization of pulsed deposition conditions was accomplished by examining the effect of square and sine waveforms, and pulse polarity, on the quality of copper deposition into sulfuric and oxalic acid-anodized templates. Pulsed square waveforms produced better pore-filling than pulsed sine waveforms. For sine wave depositions, the oxidative/reductive pulse polarity was more efficient than the commonly used reductive/oxidative pulse polarity. For square wave depositions into sulfuric acid grown pores, the reductive/oxidative pulse polarity produces more uniform pore-filling, likely as a result of enhanced resonant tunneling through the barrier layer and reoxidation of copper in faster filling pores. |
