Next generation solar cells

From the point of view of buildings, the most obvious renewable electricity source is the solar cell. High unit cost is the barrier which is preventing production achieving economies of scale. But here again things could be about to change. The solar cells of the future are likely to use thin film technology, for example titanium-oxide coated nanocrystals with ruthenium dye which mimic photosynthesis and which are now being developed in Switzerland. They absorb light strongly in the red and green parts of the visible spectrum. They should prove to be a fraction of the cost of silicon-based cells.

The next step in the progression is to create cells which absorb light in the infra-red part of the spectrum. These would be coated with

Part Gratzel Cell

Figure 21.2

Compact fuel cell hydrogen generator (courtesy of New Scientist)

a dye that is transparent yet still absorbs enough in the invisible part of the spectrum to provide electricity. Michael Gratzel of the University of Lausanne estimates that a 10 per cent conversion rate should be possible (New Scientist, 23 January 1999, p. 40). So, being transparent, they will have an application for windows as well as roofs.

Creating the solar cell which will use an organic solid to replace the liquid electrolyte of conventional cells is Gratzel's latest objective. Others are looking at capturing energy using biological rather than electrochemical cells. This is literally mimicking natural photosynthesis; in current terms, 'biomimicry'.

A chance discovery in a laboratory could be the key to the ultimate breakthrough in solar cell technology. It resulted from etching silicon with a powerful laser hundreds of billions of times brighter than the sun. The result was a jet black structure of microscopic spikes which absorbs 97 per cent of visible light. What really surprised the researchers was that it absorbs 97 per cent of infra-red part of the spectrum and even extends into the microwave end of the spectrum. Normal grey silicon is transparent to infra-red light. Not only does this create a whole new field of opportunity for communications it could also herald the birth of much more efficient solar cells. A normal silicon cell will absorb only about half the light that falls on it. At 97 per cent absorption rate the black silicon photovoltaic cell could represent a quantum leap in efficiency and therefore cost effectiveness (New Scientist, 13 January 2001, pp. 34-37).

In 2004 it was reported that a team in the Los Alamos National Laboratory in New Mexico had found a method of considerably increasing the efficiency of crystalline solar cells. Normally a single photon knocks one electron out of the crystal structure creating a current. However, when a high energy photon hits a nanocrystal semiconductor the extra energy liberates two or even three electrons. A solar cell which

Figure 21.2

Compact fuel cell hydrogen generator (courtesy of New Scientist)

employs this technology could convert 60 per cent of solar energy into electricity. The theoretical limit of conventional solar cells is 44 per cent (Physical Review Letters, vol. 92, pp. 186, 601 and reported in New Scientist, 15 May 2004, p. 16).

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

Get My Free Ebook


Post a comment