5. Technology Developments

5.1 Thin films

Thin film technologies are set to increase their share of PV manufacturing capacity in 2002 as a number of companies start to manufacture in volume from their new plants, or expand their existing production levels. These technologies are based predominantly on inorganic thin film materials such as amorphous silicon, cadmium telluride and copper indium (gallium) diselenide.

Efforts continue to enhance the performance of these thin film cells as demonstrated by scientists at the Institute for Photovoltaics (IPV) at the Research Center, Jülich who have reported this quarter a stable efficiency of 11.2 per cent for a square centimeter area silicon thin film solar cell. The cell efficiency after over 1000 hours of sun exposure was a stable 11.2 per cent.

The next step is to apply the technology to larger solar modules. These silicon thin film solar cells consist of several layers formed by deposition on a glass substrate. The first layer is a transparent conductive oxide (TCO). Sunlight passes through this to fall on the silicon layers. The best results have been achieved with cells having more than one silicon layer, which are situated one above the other. In the 11.2 per cent efficient cell, a layer of amorphous silicon was in tandem with a layer of micro-crystalline silicon. At Jülich, process technology for larger glass substrates (30 x of 30 square centimeters) is being put in place.

The silicon coating is functioning already; systems for metallic oxide coating as well as laser scribing are to be inaugurated in the second half of the year. In addition, the Institute is cooperating with RWE Solar GmbH, which already manufactures 0.6 square meter sized modules based on amorphous silicon. A module with the new tandem structure with an active area of 644 square centimeters showed a starting efficiency of 10.3 per cent.

This used a glass substrate already pre-coated with a commercial metallic oxide (TCO). Jülich scientists are planning to incorporate zinc oxide as the TCO, as used in the 11.2 per cent cell.

Honda has marked its presence on the PV scene by announcing their development of a solar cell enabling a 40% production cost reduction. The new cell, to be set up at Honda's production bases at home and abroad, will go on sale in cooperation with housing makers as early as fiscal 2003, Honda officials have said. One cell measures 1 square meter and is made of a thin film of copper indium gallium diselenide. Honda officials said they will soon start using new cells at a factory in Shizuoka Prefecture and that they expect the cells to produce a total of 100,000 kilowatt-hours of electricity a year in January next year, when it will be using a total of 1,000 such cell units there.

5.2 Organic cells

During the past three months, there have been a number of news items in regard to the development of organic cells. The potential use of organic materials in solar cells has been exemplified by the use of organic dye sensitizers in Gratzel type cells, now in the early stages of production in Australia at Sustainable Technologies International. These use an organic dye to absorb light, coupled to an inorganic semiconductor (titania) in a liquid mixture or gel. However, like inorganic semiconductor thin film cells, these cells also need tin oxide coated glass electrodes (which are high cost and mechanically rigid), and the packaging required to hold in the liquid or gel is a source of potential unreliability in the long term.

Recent announcements show growing effort and progress in the use of solid state organic cells which have the potential for a broad range of lightweight, flexible product configurations as well as low cost.

Scientists from the Fraunhofer Institute for Solar Energy Systems ISE are investigating and developing simple layered structures using electrically conductive plastics. In addition to increasing the lifespan of these cells, they are working on improving the conversion efficiency, which is currently at three percent. One of their approaches is to modify surfaces: plastics are usually smooth, and hence they reflect light. However, their surface, or even the photoactive layer itself, can be structured cheaply and over large areas by embossing them. Backed by many years of experience in this field, they have succeeded in creating fine patterns that efficiently trap sunlight in the cells.

Scientists at the University of California reported in the journal Science that they have come up with a hybrid material combining aspects of inorganic and organic cells. The material combines polymers with semiconducting rod-shaped molecules, and boasts a power conversion efficiency of 6.9 per cent.

BP Solar and SolarAMP, L.L.C. have announced that they have established a joint effort focused on developing the first commercial solid-state (organic) molecular photovoltaic (PV) module. This relationship aims to leverage SolarAMP's extensive research base in molecular PV and BP Solar's considerable expertise in PV manufacturing technologies.

BP Solar and SolarAMP will specifically address removal of the need for a liquid electrolyte in their joint development program. Realizing the commercial production of organic cells may be expected to take many years. The status of the current technology can be considered to be analogous to that of current inorganic thin films fifteen, or more, years ago. However, it is noteworthy that the leading PV manufacturer, Sharp, has announced this quarter, plans to mass-produce a 50% cheaper solar panel based on the use of organic pigments.

6. Upcoming events

Extracted from on line sample edition