Xiaofei Han

Graduation Semester and Year

2011

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering

Department

Materials Science and Engineering

First Advisor

Meng Tao

Abstract

Electrodeposition has the advantages of low-cost, high-throughput and large-area processing which is particularly suitable for solar cells fabrication. Two common metal oxides prepared by electrodeposition are discussed here, ZnO and Cu2O. ZnO is largely used in the solar cells as the window and transparent contact material. Cu2O is potential absorption material for next generation solar cell. n-type doping of these metal oxides was revealed during electrochemical deposition. For naturally n-type ZnO, n-type doping is achieved by substituting the cation (Zn) with a group III element (Al, Ga and Y) and for naturally p-type Cu2O, n-type doping is realized by substituting the anion (O) with a halogen (Cl). In both cases, the doping mechanism is believed to be co-precipitation of either ZnO with group III metal oxide (Al2O3, Ga2O3 and Y2O3) or Cu2O with Cu halide (CuCl). Cl doped Cu2O films were electrodeposited on Cu coated glass substrate. Photocurrent measurement determined its n-type conductivity. The resistivity of Cl doped Cu2O was calculated through IV relationship and the lowest resistivity of Cl-doped n-type Cu2O is around 7 O-cm which is suitable for solar cell application. Photocurrent measurement confirms the conductivity of this Cl-doped Cu2O is n-type. XRD shows the Cl-doped Cu2O is pure Cu2O and SEM shows the grain of Cu2O is small, about 100 nm. Once p-type Cu2O is realized, a p-n homojuction Cu2O cell with reasonable high efficiency can be achieved. Al, Ga and Y doped ZnO deposited by electrodeposition shows high transmittance, low absorbance and low resistivity. The minimum sheet resistance is 1.5 O with Y doped ZnO and the co-responding resistivity is 6.3 x 10-5 O-cm calculated by a parallel circuit model from stack sheet resistance. Different annealing conditions were used for lowest resistivity of ZnO realization. A UV-vis spectrum was used for transmittance and absorbance observation. XRD profiles show the ZnO doesn't mix with ITO after annealing and the SEM images show Y doped ZnO is hexagonal shape with sub-micro grain size. Thermal stability test shows this Y doped ZnO can still maintain low resistivity and high reflectance after 500 °C annealing in N2 ambient. This low resistance and high transmittance ZnO can be used as either top transparent contact or back reflector in the thin film solar cell.

Disciplines

Engineering | Materials Science and Engineering

Comments

Degree granted by The University of Texas at Arlington

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