This paper presents a structure-property model for carbon fiber derived from a polyethylene (PE) precursor that relates tensile modulus to the elastic properties and angular distribution of constituent graphitic layers, as measured using wide-angle x-ray diffraction of individual carbon fiber filaments. The observed relationship and interpretation of data using a uniform-stress model has revealed fundamental differences in the nature of the microstructure present in carbon fiber produced from polyethylene compared to carbon fiber produced from polyacrylonitrile (PAN) or pitch precursors. Specifically, it was found that the shear modulus, indicative of the shear between adjacent graphitic layers of the carbonized fiber is lower for polyethylene-derived carbon fiber than for PAN- or pitch-derived carbon fiber, suggesting that the covalent CC sp3 crosslink density connecting adjacent graphitic layers in PE-derived carbon fiber is reduced. This structure that is less crosslinked is anticipated to be easier to orient during carbonization and high-temperature graphitization processes, yielding a highly oriented structure necessary for high tensile modulus.

To develop low-cost carbon fiber, The Dow Chemical Company and others have explored the sulfonation of polyethylene fibers as an alternative to the incumbent poly(acrylonitrile) route. Although the process of polyethylene sulfonation and subsequent thermal carbonization in an inert atmosphere has been known to provide carbonaceous material for over 35years, we have found the chemical understanding of this transformation to be insufficient. Herein, we report a series of studies that have led to our current understanding for both the sulfonation and subsequent thermal treatment steps. Sulfonation of hydrocarbon model compounds yields completely conjugated and functionalized products. Spectroscopic data suggest that sulfonated polyethylene is similar; containing extended conjugated systems with sulfonic acids and various other oxygen-containing functional groups. Near-Edge X-ray Absorption Fine Structure data have identified that between 150 and 200°C the polymer undergoes a cross-linking step, while evolved gas analysis has identified concomitant release of SO2 and H2O. Above 600°C, H2 is produced and a graphenic carbon microstructure is obtained.

L'invention concerne des procedes pour preparer des polymeres carbones, tels que des fibres de carbone, consistant a sulfoner un polymere au moyen d'un agent de sulfonation qui renferme un gaz SO 3 afin de former un polymere sulfone ; a traiter le polymere sulfone au moyen d'un solvant chauffe, la temperature du solvant etant d'au moins 95 °C ; et a carboniser le produit resultant en le chauffant a une temperature comprise entre 500 et 3000 °C.

Despite significant growth in photovoltaics (PV) over the last few years, only approximately 1.07 billion kWhr of electricity is estimated to have been generated from PV in the US during 2008, or 0.27% of total electrical generation. PV market penetration is set for a paradigm shift, as fluctuating hydrocarbon prices and an acknowledgement of the environmental impacts associated with their use, combined with breakthrough new PV technologies, such as thin-film and BIPV, are driving the cost of energy generated with PV to parity or cost advantage versus more traditional forms of energy generation. In addition to reaching cost parity with grid supplied power, a key to the long-term success of PV as a viable energy alternative is the reliability of systems in the field. New technologies may or may not have the same failure modes as previous technologies. Reliability testing and product lifetime issues continue to be one of the key bottlenecks in the rapid commercialization of PV technologies today. In this paper, we highlight the critical need for moving away from relying on traditional qualification and safety tests as a measure of reliability and focus instead on designing for reliability and its integration into the product development process. A drive towards quantitative predictive accelerated testing is emphasized and an industrial collaboration model addressing reliability challenges is proposed.

Multilayer oxide thin film stacks of aluminum doped zinc oxide (AZO) and tin doped indium oxide (ITO) have been sequentially deposited on soda lime glass substrates by RF sputtering of AZO and ITO ceramic targets at a substrate temperature of 150 °C. The ratio of the AZO thickness to the ITO thickness is varied while keeping the total thickness of the stack constant. The electrical and optical properties of the multilayer stacks have been investigated as a function of this ratio and the number of interfaces. The experimental results are compared and their impact on device performance is demonstrated by simulations with validated AMPS-1D models. XRD and microscopy measurements have been carried out to understand the microstructure of the multilayer system and to establish its correlation with the opto- electric properties. The results have been evaluated for use of these multilayer TCO stacks as potential window layers for the photovoltaic solar cell applications.

The lifetime-limiting failure mechanisms of CuInGaSSe (CIGSS) solar devices made by Shell Solar Industries (SSI) were investigated. In our study, SSI minimodules were exposed to dry-heat 85°C, damp-heat 85°C/85% RH and aerobic and anaerobic room temperature and 85°C water baths. After 200 hours exposure to moisture-containing environments, the average device performance decreased by more than 30% that of the initial state. The observed degradation was primarily due to losses in short circuit current density (Jsc) and fill factor (FF). The as-received device layers were relatively dense and free of voids. Interestingly, unreacted Cu-Ga particulates were found at the Mo-CIGSS interface. Corresponding with these particulates, CIS-rich defects were found within the bulk CIGSS material. Post-environmental weathering, Kirkendall-like voids were found in the Al:ZnO and CdS layers of these devices. Additionally, ToF-SIMS analysis revealed the Cu-Ga/CIS defects were enriched in Na and O. Our results indicate that in addition to moisture-induced failure of the window layers, the unreacted Cu-Ga particulates and the corresponding CIS-defects may facilitate moisture and/or oxygen-induced failure of these devices.

The solar power industry is enjoying rapid growth, but challenges remain to produce new photoactive materials with the proper balance of cost and efficiency. Much of the fundamental science concerning alternative materials has not yet been elucidated. Using ab initio density functional theory to predict band structure and densities of state for 3-D unit cells, four binary and ternary silver selenides have been identified as prime candidates for use as an absorber layer in photovoltaic cells. Thin films of these silver selenides were grown, and morphology, stoichiometry, and structure were analyzed using SEM, EDS, and XRD. Optoelectronic characterization of the films was performed using UV-Vis, Hall Effect, and photoluminescence measurements. These data were used to judge the quality of the materials and to confirm the accuracy of the predictive capability of calculations.

In our study, Shell Solar Industries (SSI) minimodules were subjected to dry heat (85°C), damp heat (85°C/100% RH), and anaerobic/aerobic 85°C water baths. After 168 hrs exposure to moisture-containing environments, the SSI power generation decreased by over 50% of that of the original state. Analytical characterization performed before and after the exposure identified degradation of the Al:ZnO and Mo layers as likely device failure routes. To elucidate the observed degradation mechanism, individual Al:ZnO and Mo films were sputtered onto borosilicate glass and exposed to both 85°C/100% RH and a room temperature water bath. After 24 hrs the resistivity and optical transmission of the Al:ZnO films increased significantly following both exposure methods. XPS surface analysis of the films revealed changes in the O to Zn bonding ratio suggesting film hydration may have occurred. In addition, after 48 hours by both exposure methods the Mo films corroded, and the film resistivities increased. Our results show Al:ZnO layer degradation limits the lifetime of CIGSS based PV devices, whereas Mo degradation is considered a non-lifetime-limiting failure.