Thesis (Ph.D.)--McMaster University, 2003. / Advisor: A.H. Kitai. Includes bibliographical references (leaves 193-199). Also available via World Wide Web.

Organic solar cells (OSCs) have attracted significant attention due to their potential of large area solution fabrication capability at low-cost. For bulk heterojunction (BHJ) OSCs, a thin film of transparent conducting indium tin oxide (ITO), coated on glass or flexible plastic substrate, is widely used as a front electrode. However, indium is not abundant on Earth. Its price has increased continuously over the past 10 years and will likely become an obstacle for the commercialization of OSCs at low cost. Aluminum-doped zinc oxide (AZO) is a promising ITO alternative due to its advantages of high electric conductivity, optical transparency, non-toxicity and low cost. However, reports on OSCs using AZO electrode are quite limited, due to the relatively lower power conversion efficiency (PCE) of AZO-based OCSs as compared to that of ITO-based OCSs. This work focused on studies of high performance AZO-based OSCs through AZO surface modification, absorption enhancement and process optimization. The optical and electronic properties of AZO film including transmittance, sheet resistance, surface morphology and surface work function were characterized. AZO-based OSCs with conventional and inverted structures were fabricated. It was found that AZO-based OSCs with inverted structure demonstrated superior performance than the ones with conventional structure. The inverted structure avoids the use of acidic PEDOT:PSS hole transporting layer, allows the improving of the absorbance of the OSCs and therefore its efficiency. An AZO front transparent cathode was used for application in high performance inverted BHJ OSCs. The photoactive layer consisted a blend of poly[[4,8-bis[(2- ethylhexyl)oxy] benzo [1,2-b:4,5-b'] dithiophene-2,6- diyl][3-fluoro- 2-[(2-ethylhexyl) carbonyl]thieno[3,4-b]thiophenediyl]](PTB7):3'H-Cyclopropa[8,25][5,6]fullerene- C70- D5h(6)-3'-butanoicacid, 3'-phenyl-, methyl ester (PC70BM). A structurally identical control OSC having an ITO front cathode was also fabricated for comparison studies. The structure of OSCs was optimized to achieving absorption enhancement in the active layer. AZO and ITO were modified with a 10 nm thick solution-processed ZnO interlayer to facilitate the efficient electron extraction. The results revealed that bilayer AZO/ZnO and the ITO/ZnO cathodes possess similar electron extraction property. AZO layer has a transparency cutoff at wavelength < 380 nm, results in a slight decrease in the short-circuit current density (JSC). However, the decrease in JSC is very small because the main energy of solar irradiation falls in the spectrum with wavelength > 380 nm. It shows that AZO-based OSCs have a promising PCE of 6.15%, which is slightly lower than that of a control ITO-based OSC (6.57%). AZO-based OSCs, however, demonstrate an obvious enhancement in the stability under an ultraviolet (UV)-assisted acceleration aging test. The significant enhancement in the stability of AZO-based OSCs arises from the tailored absorption of AZO electrode in wavelength < 380 nm, which serves as a UV filter to inhibit an inevitable degradation process in ITO-based OSCs due to the UV irradiation. In order to further investigate the degradation mechanism of OSCs under UV exposure, the change in charge collection characteristics of the OSCs made with ITO/ZnO and AZO/ZnO front cathode before and after UV exposure was examined. It was found that there was an obvious decrease in the charge extraction efficiency of ITO-based OSCs after UV exposure, while there was no observable change in the charge extraction efficiency of OSCs made with AZO/ZnO cathode under the same acceleration aging test. This work demonstrates that AZO is a suitable ITO alternative for application in OSCs, offering an improved device stability, comparable PCE and cell fabrication processes with an attractive commercial potential.

Zinc oxide (ZnO) is a II-VI semiconductor material that offers tremendous potential as a light emitter in the blue-to-UV range. It has a wurtzite structure, and a direct band gap that can be tuned from 3.0 to 4.0 eV by alloying with Cd or Mg, respectively. In this work, ZnO thin films were grown by metalorganic chemical vapor deposition (MOCVD) on n-Si 2 ° off (100), amorphous glass, n-GaAs (100), and c-plane sapphire substrates. Diethyl zinc (DEZn) and tert-butanol (TBOH) were chosen as precursors. For the first time, Second Harmonic Generation Imaging was applied to the mapping of ZnO epilayers. The images obtained highlighted the polycrystalline character of the thin films, and provided insight as to the growth mode of ZnO on Si. The influence of substrate temperature on the structural properties of the epilayers was investigated by X-ray diffraction and optical microscopy. Grain sizes as high as 54 nm were measured. The optimum temperature range for this system proved to be 450 – 500 °C. The influence of the VI:II ratio during growth on the optical properties of the epilayers was studied by UV-vis-near IR spectroscopy. The lowest Urbach tail E0 parameter was measured for material grown at a VI:II ratio of 18:1. The films’ free electron concentration was shown to decrease by over two orders of magnitude, from 1019 to 1017 cm-3, as the VI:II ratio increased from 10 to 60:1. This decrease in carrier concentration with rising VI:II ratio was paralleled to the surge at 12 K of a photoluminescence (PL) emission band characteristic of p-type ZnO. The band gap energies extracted from room temperature transmission spectra ranged between 3.35 and 3.38 eV, in agreement with the value of 3.35 eV measured by room temperature PL. Moreover, variable temperature PL spectra were recorded between 12 and 298 K on ZnO grown on Si. The 12 K spectrum was dominated by a donor-bound exciton (D°X) at 3.36 eV, while the 298 K scan displayed strong free exciton emission (FX) at 3.29 eV. The width of the D°X band proved to be as narrow as 7 meV. The intensity ratio between the room temperature near-band edge emission and the defect-related green band was as high as 28:1, highlighting the optical quality of the layers deposited in this work. The electrical properties of the thin films were studied by Hall measurements (van der Pauw configuration), and a maximum room temperature mobility of 11 cm2/Vs was recorded. Furthermore, a palladium (Pd) Schottky barrier diode on ZnO was fabricated. The barrier height and ideality factor were calculated from current–voltage measurements to be 0.83 eV and 1.6, respectively. The capacitance–voltage curve of the diode yielded a carrier concentration in the depletion region of 8·1017 cm-3. This study has shown that the optical and electrical properties of ZnO depend strongly on the growth conditions employed. A suitable choice of growth parameters can yield high quality ZnO that may be used for various devices. Keywords: Hall, MOCVD, optical spectroscopy, photoluminescence, Schottky barrier diode, SH Imaging, X-ray diffraction, ZnO.

Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). Includes bibliographical references (p. 241-266). Also available via the World Wide Web.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Title from PDF t.p. (viewed Feb. 3, 2010). Additional advisors: Derrick R. Dean, Sergey B. Mirov, Sergey Vyazovkin, Mary Ellen Zvanut. Includes bibliographical references (p. 122-145).

Electrical and optical properties of the (N,Ga)-doped ZnO films have been studied. Three growth regions were identified to obtain ZnO films with different conduction types depending on the N/Ga flux ratio in doping process. The PL spectra show evident competition between neutral-donor bound exciton (D0X) and neutral-acceptor bound exciton (A0X) according to the N/Ga ratio. From the temperature-dependent PL spectra, the nitrogen acceptor level was identified to be about 126 meV in (N,Ga)-doped p-type ZnO. / For nitrogen doping of ZnO thin films, DMHy was used as the nitrogen dopant source. A narrow temperature window from about 500&deg;C to 550&deg;C for efficient nitrogen doping was identified. However, p-type ZnO was not obtained by nitrogen mono-doping, which results from the low solubility of N and the self-compensating effect of native defects, and/or N-induced complexes. By co-doping N with Ga in proper ratios, p-type ZnO films were successfully achieved with a high hole concentration of 3.51 x 1017 --2.41 x 1018cm-3, Hall mobility of 1.1 --4.29 cm2/V-s and resistivity of 0.6 -- 16.2 O cm. But the conduction type critically depends on the growth conditions. Based on the successfully fabrication of (N,Ga)-doped p-type ZnO, a p-ZnO:(N,Ga)/n-ZnO homojunction was fabricated. The I-V measurement shows clear rectifying behavior with a turn-on voltage of about 3.7 V. / Further investigation of the effect of N/Ga doping ratios on the conduction type of ZnO samples reveals that successful doping depends much on engineering a stable local chemical bonding environment. Under mono-doping conditions (via N-Zn4), nitrogen solubility is limited and nitrogen acceptors are readily compensated by native donors and/or N-related donors; under appropriate N/Ga flux ratios, cluster-doping (via Ga-N3O and Ga-N4) can be realized to achieve p-type ZnO; while excessively high N/Ga ratios cause the doped ZnO n-type conductivity again, which may be because that under excessively high N/Ga ratio range, N-Zn4 configuration dominates and thus cause more N-related donors and degrade the ZnO film quality, similar as the mono-doping case. By tuning the N/Ga ratio in doping, it is expected to create appropriate chemical environments to enhance the formation of desired dopant species for stable p-type ZnO. / In this work, Metal-organic chemical vapour deposition (MOCVD) growth of ZnO and its p-type doping have been studied. The group V element N was used as primary dopant to make ZnO p-type. In the growth of ZnO by MOCVD, it was found that the structural and morphological properties of deposited ZnO strongly depend on growth conditions. Low VI/II ratio and high growth rate favor the growth of ZnO nanostructures (nanowires, nanobelts); while high VI/II ratio and low growth rate favor the growth of ZnO thin films. / The semiconductor ZnO is currently gaining intense interest in the research community because of its prospect in optoelectronic applications, such as blue/ultraviolet emitters and detectors, and high speed electronic devices. However, making reliable and reproducible p-type ZnO is still a bottleneck, which impedes the practical application of ZnO-based devices. The difficulty is mainly due to the self-compensation effect of native defects and the low solubility limit of acceptor dopants. Although substantial research is currently being carried out worldwide towards this goal, the effective p-type dopant and its doping process have not yet been identified. / Wang, Hui. / "Apr 2008." / Adviser: Aaron H. P. Ho. / Source: Dissertation Abstracts International, Volume: 70-03, Section: B, page: 1860. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 204-217).

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 140-151).

The physical properties of cadmium sulfide and zinc oxide thin films, deposited from aqueous solution, were investigated using electron and x-ray diffraction techniques. The conventional method and two new methods were used to deposit cadmium sulfide thin films. Moreover, a new method for the deposition of zinc oxide was devised. Experiments were conducted on the cadmium sulfide thin films in order to make their semiconducting properties favorable for use as solar cells. Cds-Cu(x)S solar cells were fabricated, and their I-V characteristic curves plotted, using an X-Y recorder. The photovoltaic effects in chemically deposited Cds films have been clearly demonstrated.

Thesis (M.S.)--Ohio University, November, 2003. / Title from PDF t.p. Includes bibliographical references (leaves 58-62).