After Gutenberg

Sharp’s thin-film solar PV modules are covered with tempered glass for increased strength and minimum reflected surface glare. The Amorphous / Microcrystalline Thin-Film Tandem Cell design achieves some of the industry’s highest levels of conversion efficiency for thin-film, silicon-based solar cells. Since the silicon layer is only about 2 �m thick, roughly 1/100th as thick as conventional polycrystalline solar cells, cells with large surface areas can be manufactured at a competitive price.

On several different occasions this blog has mentioned BIPV (Building Integrated Photo Voltaic) systems, thin film photo voltaic materials, and even Power Glass, which is the use of very thin semi-transparent coatings and films that create large area monolithic solar cell structures that you can see through. Xsunx has focused on patented processes, such as reel-to-reel manufacturing techniques and multi-terminal cell structure designs, in the hope of introducing such thin film flexible plastics into commercial architecture.

Power Glass is a way to combine the use of natural day-lighting with a photo voltaic source of energy. Nevertheless, many public use buildings require lighting at night.

Add to the list of potentially energy-efficient construction a product from Sharp Solar that offers passive lighting by day and LED lighting by night. Expected to go on sale in 2007, Sharp’s LumiWall is powered by thin-film solar panels inside glazing. But, these panels not only harvest energy from sunlight, with integrated light-emitting diodes, they provide a source of lighting.

Sharp uses something they call “crystal thin film see through tandem cell”, i.e., the solar array is a laminate of amorphous silicon and crystal thin film silicon.

Rather than thin slices of silicon, we soon may see low-cost production of dye-sensitized solar cells. Investment costs for fabrication are low, and materials of what also known as Graetzel cells* may become cheap in a large-scale production. The lower costs of manufacturing dye-sensitized solar cells may compensate for lower efficiency compared to solid-state cells.

* Note: In 1991, Michael Graetzel reported that controlled formation of highly organized mesoporous titania thin films can achieve photo-sensitization over a wide-band-gap. “Dye excitation is followed by electron injection into the TiO2 and by dye re-charging via a redox electrolyte (mostly I-/I3-). Electrons are transported in the TiO2 nano-particles to the front contact, which consists of a transparent conductive oxide layer (TCO). The contact to the redox electrolyte is made by a (catalyst-coated) back contact. For backside illumination, that contact can also be made transparent using a TCO window.”

What sort of efficiency can be demonstrated? A Nature article (Subscription required) relates that, because of the high surface area of a 10-micron-thick, optically transparent film of titanium dioxide plus ideal spectral characteristics of a mono-layer of a charge-transfer dye, a high proportion of the incident solar energy flux (46%) can be harvested. Tests have shown “exceptionally high efficiencies for the conversion of incident photons to electrical current (more than 80%). The overall light-to-electric energy conversion yield is 7.1-7.9% in simulated solar light and 12% in diffuse daylight. The large current densities (greater than 12 mA cm-2) and exceptional stability (sustaining at least five million turnovers without decomposition), as well as the low cost, make practical applications feasible.”