| dc.description.abstract | In an attempt to increase the maximum theoretical efficiency of solar cells, one proposed device is called intermediate band solar cells (IBSC). The candidate material system chosen for this study is nitrogen doped cuprous oxide, which is reported to have an intermediate band, in conjunction with zinc oxide, ZnO/N:Cu2O. This thesis has three main parts, a literature study, an experimental material study of Cu2O and Aluminium doped ZnO (AZO), and finally an attempt at experimentally producing an AZO/N:Cu2O IB solar cell was made.
The literature study revealed that the largest challenges are the difficulty of producing monocrystalline Cu2O without CuO or Cu, the high resistivity of Cu2O, and charge transport and recombination at the AZO/Cu2O interface. Cu2O and AZO need to be deposited with as high crystalline quality and low resistivity as possible.
The purpose of the material study was to optimize deposition parameters for thin films produced by pulsed laser deposition (PLD). X-ray diffraction (XRD) and four point probe were the main characterization techniques, but some X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) was also performed on select Cu2O films. The best AZO film produced was deposited at a substrate temperature of 400 degrees celcius and a substrate-target distance of 55 mm. It had a resistivity of 3.69 x 10^(-3) Ohm cm and its (002) oriented crystallite size of 84 A;.The optimal Cu2O film was produced with a substrate temperature of 750 degrees celcius and was either produced with a flow rate of 3 sccm of O2 and no N2, or with 3 sccm of O2 and 30 sccm of N2. The film produced with no nitrogen had a larger (111) oriented crystallite size, 336 Angstrom to 313 Angstrom; , whilst the film with 30 sccm of N2 had a lower resistivity 93 Ohm cm to 217 Ohm cm.
For the purpose of producing an IB material, nitrogen doping of the Cu2O films was attempted by adjusting the flow ration of N2/O2. For the conditions used in this thesis, XPS results indicate negligible nitrogen inclusion.
The last part of the thesis is design and fabrication of a complete solar cell structure, using the optimal parameters from the materials study. The structure proposed was Glass Substrate/Mo electrode/AZO/ZnO/N:Cu2O/Au electrode. In these preliminary tests, the design exhibited ohmic rather than diode characteristics.This was determined to be due to oxygenation of the Mo electrode. | |
