The new photovoltaics

Silicon photocells are seen in many places but the technology is severely limited. Silicon will never give tightly rollable devices let alone transparent ones or even low cost power generation on flexible substrates. No hope here of strong thermo-photovoltaic effects, where heat generates the electricity when light does not. No hope of generating useful power when the light hits at a narrow angle or is reflected from windows or otherwise polarised. The typical silicon photovoltaic unit is heavy, inflating transport and installation costs and it may break into dangerous shards of glass. Amorphous silicon gives thinner layers but it has stability problems and all the above limitations as well, so, if we want a breakthrough we have to look elsewhere. There is certainly no chance of either option being printed at high speed, reel to reel on low cost substrates using low temperature processes.

Fortunately there are many new alternatives and they are the subject of the major conference, Photovoltaics beyond Conventional Silicon 17-18 June in Denver Colorado. Organiser Dr Harry Zervos of IDTechEx says, "We chose the title carefully because it is not just a matter of escaping from silicon. Silicon nano-ink proprietary processes are developed by Kovio and Innovalight for example; they do promise many of the features that conventional silicon can never achieve. However, nothing will serve all the needs and this unique conference will give the full picture, bringing it alive with visits to see world renowned local facilities." To further enrich the event, there will be optional masterclasses by international experts.

All the new forms of photovoltaic unit employ thin films and, to increase output and reduce cost, they are increasingly printed reel to reel. For example, G24 Innovations prints Dye Sensitised Solar Cells DSSC by ink jet and Nanosolar is building two factories to ink jet print Copper Indium Gallium diSelenide CIGS photovoltaics. Others claim a better result, but not necessarily a lower cost, by using RF sputtering or chemical vapour deposition for example and there are exciting new technologies being proven such as Optomec Aerosol jet ® deposition which overcomes some disadvantages of ink jet. Increasingly, the new photovoltaics will be co-deposited with batteries and other components. It will even form part of the new industries concerned with stretchable electronics, not least in healthcare, and electronic smart packaging. We are only just beginning to grasp what will be possible. People are even working on edible electronics and electronics that morphs into different shapes. The conference will look closely at both device and production technology.

Certainly this is not just a matter of dreaming. First Solar has taken orders of over $1.5 billion in recent months in the USA and France for its thin film cadmium telluride photovoltaic units, because they are more economical than conventional silicon. These devices did not need to be printed reel to reel to achieve that success.

These are exciting times, with wristwatches being developed that charge the battery from transparent photovoltaics over the viewing glass so the battery then lasts longer than you do. Photovoltaics is in space. This has its own requirements of radiation and heat tolerance, very high efficiency and very light weight so these are being met by complex multilayer constructions using GaAs-Ge and other thin films. However, if we are to generate very large amounts of power from broad widths of tape unrolled alongside hundreds of miles of freeway, we may care little about efficiency and a great deal about cost, so the exciting new organic photocells made by high speed printing processes may be the answer, even at the 5-6% efficiency now achieved.

 

 

Some of these disparate needs are shown below:

 

 

In short, the photovoltaic business is fragmenting as it grows to tens of billions of dollars yearly. Conventional silicon will be around for at least ten years but the many large new market segments that are opening up will be served by the new photovoltaics, and eventually conventional silicon will vanish from the scene. The heavy government subsidies that prop up sales of conventional silicon photovoltaics today will no longer be necessary

To some extent, this revolution is part of the move to a $300 billion market for printed electronics. Indeed, 1500 organisations are working on printed and potentially printed electronics and electrics and by far the favourite topic is the new photovoltaics, with the largest concentration - 440 organisations - working on this aspect and several already selling new photovoltaic products. Of the developers of new PV, about half are academic, but many of these are spinning off startups. The largest number of developers is in Europe, but the USA is investing as much as any territory. In Japan, a large number of major corporations is involved, including Honda setting up reel to reel CIGS production in the last year. For this reason, the IDTechEx conference is flying in best in class speakers from all over the world. It will be a truly international event, addressing the needs of two billion people that lack access to electricity and the two billion mobile phone owners who want to avoid flat batteries and much more besides. No one will need convincing that this is a huge new industry in the making.

 

 

Attend Photovoltaics Beyond Conventional Silicon, USA, June 2008 or next month Printed Electronics Europe 2008.

 

Also read Printed Photovoltaics and Batteries: Technologies, Forecasts and Players.