CdSe solar cells with ZnTe as the window layer deposited by CSS process have shown Voc's around 630mV. However the currents were very low and also the voltages were not meeting the desired objectives. To improve the performance the contact energy at the ZnTe/Cu interface should be minimized by doping the window layer. Thermal evaporation was used to deposit ZnTe to have more control over the composition of the film. Initial experiments were done by depositing Cu doped ZnTe films on plain glass by co-evaporating both ZnTe and Cu. The conductivity was in the order of 10e3 which shows copper present in the film in the order of 1e22 S/cm³. This accomplishes a tunneling contact with the top electrode. Using the ZnTe:Cu contacts in complete devices resulted in disappointing voltages and currents. Efforts were made to deal with the poor performance of the cells. Devices were made on different types of TCO coated glass substrates but, were resulting in the same numbers which shows the type of TCO has an insignificant effect on the performance. The Cu doping has been helping in raising the Vocs but at the same time marred the currents whose effect has been unexplainable. Further experiments have been made changing the ZnTe thickness and concentration of Cu doping. Experiments were done increasing the substrate temperature as high as 5000C during ZnTe deposition and a Se flux has been introduced so as to compensate the loss of Se from CdSe at such high substrate temperature. But these experiments resulted in dismal performance indicating the domination of defects in the undoped ZnTe layer.

A new strategy was developed to switch the luminescence of semiconductor quantum dots with chemical stimulations. It is based on the photoinduced transfer of either energy from CdSe-ZnS core-shell quantum dots to [1,3]oxazine ligands or electrons from the organic to the inorganic components. Upon addition of base or acid, energy or electron transfer pathways respectively become operative, leading to changes in the luminescence of the nanoparticles. These changes are fully reversible and can be exploited to probe the pH of aqueous solutions from 3 up to 11 and this design can lead to the development of pH-sensitive luminescent probes for biomedical applications based on the semiconductor quantum dots. Secondly, an operating principle to transduce the supramolecular association of complementary receptor-substrate pairs into an enhancement in the luminescence of sensitive quantum dots was identified. This system is based on the electrostatic adsorption of cationic quenchers on the surface of anionic quantum dots. The adsorbed quenchers efficiently suppress the emission character of the associated nanoparticles on the basis of photoinduced electron transfer. In the presence of target receptors able to bind the quenchers and prevent electron transfer, however, the luminescence of the quantum dots is restored. Thus, complementary receptor-substrate pairs can be identified with luminescence measurements relying on this system and this protocol can be adapted to signal protein-ligand interactions. Thirdly, a photochromic spiropyran with dithiolane appendage to adsorb on the surface of cadmium sulfide system was designed. The properties of the resulting photochrome-nanoparticle assemblies vary significantly with the experimental conditions selected for the preparation of the inorganic component. Finally, photochromic materials based on the photoinduced transfer of electrons from CdSe-ZnS core-shell quantum dots to bipyridinium dications were developed.

Since the phase stability region of CuInSe2 (CIS) extends as wide as a few atomic percent, composition variation in a microscopic scale is nature to this material and can be detected by EPMA or TEM-EDS. As the detection volume is kept as small as possible (e.g. we used an electron probe with a diameter of 3nm to measure a TEM specimen thinned by a focused ion beam to a 80 nm thickness), the composition data fluctuate rather significantly. For a near-stoichiometric CIS film prepared by co-evaporation or a selenized film using binary selenides as precursor, the composition variations in a nanometer scale were quite distinct. Due to the tedious procedures for making TEM specimens and doing measurements, we normally used EPMA for the composition analysis. Although the composition was measured in a micrometer scale, its variation still can be detected and expressed by the standard deviation. Our results showed that the selenized films prepared by using binary selenides as precursors (they were used to make the device in this work) had much better composition uniformity as compared with the films selenized from the elemental precursors. We also found that even the time period for the selenization process was short (rapid thermal selenization) or long (conventional selenization), the composition variation did not make any changes. Since there still has problems for making devices by using rapid thermal selenization, we successfully fabricated the CIS thin-film solar cells through the conventional selenization processes. The I-V characteristics of the best CIS cell is in the following: Voc=0.398 V, Jsc=41.14 mA/cm2, fill factor (FF)=54.58%, efficiency= 9.29%. We also made a CIGS cell and found that the open circuit voltage was increased to 0.461 V. However, the efficiency was 4.42%. It still needs more effort to boost its short circuit current and fill factor.

Thesis (Ph.D.)--University of Central Florida, 2008. / Adviser: Neelkanth G. Dhere. On t.p. "x" and "y" are subscripts. Includes bibliographical references (p. 130-142).

Thesis (Ph. D.)--University of Massachusetts Amherst, 2009. / Includes bibliographical references (p. 153-161). Print copy also available.

Dissertation (Ph.D.)--University of Toledo, 2009. / Typescript. "Submitted as partial fulfillment of the requirements for the Doctor of Philosophy in Physics." Bibliography: leaves 132-148.

Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xiv, 141 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 135-141).

Thesis (M.S.)--Florida State University, 2006. / Advisor: Peter Kalu, Florida State University, College of Engineering, Dept. of Mechanical Engineering. Title and description from dissertation home page (viewed Sept. 22, 2006). Document formatted into pages; contains x, 77 pages. Includes bibliographical references.

Techn. University, Diss., 2004--Dresden.

In today's "silicon age" in which we live, field-effect transistors (FET) are the workhorse of virtually all modern-day electronic gadgets. Although silicon currently dominates most of these electronics, layered 2D transition metal dichalcogenides (TMDCs) have great potential in low power optoelectronic applications due to their indirect-to-direct band gap transition from bulk to few-layer and high on/off switching ratios. TMDC WSe2 is studied here, mechanically exfoliated from CVT-grown bulk WSe2 crystals, to create a few-layered ambipolar FET, which transitions from dominant p-type behavior to n-type behavior dominating as temperature decreases. A high electron mobility μ>150 cm2V-1s-1 was found in the low temperature region near 50 K. Temperature-dependent photoconduction measurements were also taken, revealing that both the application of negative gate bias and decreasing the temperature resulted in an increase of the responsivity of the WSe2 sample. Besides TMDCs, Group III-VI van der Waals structures also show promising anisotropic optical, electronic, and mechanical properties. In particular, mechanically exfoliated few-layered InSe is studied here for its indirect band gap of 1.4 eV, which should offer a broad spectral response. It was found that the steady state photoconduction slightly decreased with the application of positive gate bias, likely due to the desorption of adsorbates on the surface of the sample. A room temperature responsivity near 5 AW-1 and external quantum efficiency of 207% was found for the InSe FET. Both TMDC’s and group III-VI chalcogenides continue to be studied for their remarkably diverse properties that depend on their thickness and composition for their applications as transistors, sensors, and composite materials in photovoltaics and optoelectronics.