Solution Growth Of ZnO Rod Arrays And Electrodeposition Of CuSCN Hole Conductor And CuInS₂ Absorber Layer Films

The NPC solar cells have been widely studied due to their low cost and simple technique. This thesis majored on the preparation of semiconductors films for NPC cells by wet chemical methods: aqueous solution growth and electrodeposition. As the n-type electron conductor of NPC cells, the use of ZnO rod arrays has the advantage of 3D ordered structure with high specific surface area and the improvement of electron transport directly from the rod to the collection electrode. In order to protect the ZnO rod arrays from acidic etching in electrodeposition process, the electrolyte solutions used in the deposition were limited to neutral or weak basic condition.Zn(NO₃)₂/NH₃·H₂O and Zn(NO₃)₂/HMT growth systems were employed to study the aqueous solution growth of ZnO rod arrays. The highly c axis preferential aligned wurtzite ZnO rod arrays were grown. The PL measurements of the as-grown ZnO exhibited non UV emission while the defects emissions at 414nm and 493nm were obvious. The crystallinity was improved by different annealing, the result in Ar atmosphere was proved to be better by clearer UV emission and relatively stronger intensity compared with the defect emissions. Moreover, the stability of growth solution was improved by adding PEG and TEA, which adjusted driving force of the ZnO growth and promoted crystallization. After annealed in Ar, the PL spectra of the obtained rods showed high intensity of UV emission centered at 378 nm without obviously defects emissions in visible wavelength range.Stable aqueous electrolyte solution containing Cu²⁺ and SCN^- was prepared by adding TEA to chelate with Cu(II) cations. The electrolyte solutions were basic with pH in the range of 8.5⁹ and could be used in the electrodeposition of CuSCN as hole conducting layer on ZnO substrates. The dense p-type CuSCN thin films with Eg=3.88 eV and high transmittance were successfully deposited on ITO glass substrates at -500 mV. The decreasing of deposition potential, electrolyte concentration and deposition temperature would result in imperfect growth of CuSCN grains.The electrodeposition of CuSCN on ZnO rod arrays was studied. An energy band gap model and a thermal activation mechanism for the compact filling of CuSCN in the gaps of ZnO rod arrays was proposed based on FESEM observation, LSV measurements on different substrates and the current density transients on ZnO rod arrays at different temperature. The electrodeposited CuSCN/ZnO_rod interpenetrating heterojunctions exhibited clear rectification, indicating good electrical contacts formed between the internal surface of ZnO rod arrays and the embedded CuSCN. The one deposited at 0 oC had n=3.3, series resistance of 130Ω, the rectification ratio at±0.8V was 12.07.The compact chalcopyrite CuInS₂ films were also electrodeposited by neutral and weak basic aqueous electrolyte solutions with pH from 7.2 to 10.2 through adding chelating agents CitNa and TEA. pH of the electrolyte had great influence on the crystalline phase formed in the annealed films, which restricted proper deposition potential to a narrow range nearby -1200 mV. If a lower potential was applied, the deposited film tended to be loose, meanwhile a higher one leaded to formation of CuIn5S8 impurity phase. The band gaps of the annealed films were in the range of 1.29 eV to 1.46 eV, depending on pH. The electrodeposition of CuInS₂ on ZnO rod arrays was achieved, and the obtained CuInS₂/ZnO_rod heterstructure had nonlinear rectification characteristics with VOC=320mV and ISC=0.236mA/cm2 under irradiation with 70 W intensity.