Tailoring thin films additives

StiU another method used to produce PV cells is provided by thin-fiLm technologies. Thin films ate made by depositing semiconductor materials on a sohd substrate such as glass or metal sheet. Among the wide variety of thin-fiLm materials under development ate amorphous siUcon, polycrystaUine sUicon, copper indium diselenide, and cadmium teUuride. Additionally, development of multijunction thin-film PV cells is being explored. These cells use multiple layers of thin-film sUicon alloys or other semiconductors tailored to respond to specific portions of the light spectmm. 

Figure 2). Orientation of the films is used to tailor and control the CTE, and the low dielectric thin film layers provide more controlled impedance and reduced crosstalk than other substrate materials. In addition to MLBs, ordered polymer films can be used to advantage in multichip molecules where silicon chips are directly bonded to the interconnect substrate. The very low permeability of PBO and PBZT films will protect the chips from moisture. Flexible circuitry is another promising application area for these films. 

This chapter shows the potential of sol-gel chemistry for the synthesis of solution precursors used in the CSD of thin films with electrical properties. CSD is an alternative low-cost deposition technique to the vacuiun and high-temperature deposition methods that, in addition, makes it possible to obtain stoichiometric and uniform thin films. Electrical properties of electroceramic thin films are extremely sensitive to processing, microstructure, heterostructure, crystallinity, or charged defects of the film. Sol-gel offers the chance of controlling these film characteristics and therefore the functional properties by tailoring the solution chemistry and the thermal conversion of the as-deposited gel layer into a ceramic film. 

Modified Leverett Function Appropriate for Fuel Cell Media The standard Leverett function has been found to be appropriate for qualitative matching of the flow characteristics through the media however, actual measurements of PEFC diffusion media show different quantitative behavior. Kumbur et al. [47] presented a modified Leverett function appropriate for thin-film fuel cell DM to estimate the capillary pressure as a function of liquid saturation and hydrophobic additive content This empirical fit was derived from the direct measurement of capillary pressure-saturation for different types of DMs (cloth and paper) with PTFE content ranging from 0 to 20% of weight and a nnicrop-orous layer. Figure 5.35 depicts the measured capillary pressure (Pc) versus nonwetting liquid saturation for carbon paper DM tailored with 20% PTFE content. The nature of the capillary pressure-saturation curves exhibits a continuous S shape, rather than J shape, and yields four inflection points. For saturation leads under 0.5, the capillary pressure in the DM was fit to a modified Leverett function, appropriate for the hydrophobic pores ... 

---