Developing a single semiconducting material that can effectively tap sunlight, and generate easily separable "excitons" is the holy-grail in photovoltaic technologies. An exciton is essentially a Couloumbically bound pair of electron and a hole. These excitons, which are generated when semiconductors absorb sunlight, can be split (this is much trickier than it sounds!) and sent along opposite directions to generate a non-zero electric current, if the material system is part of a closed electric circuit. This is how a solar cell works. This also helps us understand why engineers would like a semiconductor which absorbs over the entire solar spectrum.

For making a good solar cell we need a semiconductor which (i) absorbs over the entire solar spectrum, and (ii) gives exciton sufficient time (called the "exciton lifetime" in textbooks) so that charge separation is realistically possible. Developing materials of this kind are promising from the point of view of solar cells. We set out making materials of this kind, and succeeded in finding a material that has almost full solar spectrum absorption (it is Cu doped ZnO made in a specific fashion). We do not know how promising the exciton life time etc are at the moment. We now wish to use this material system for making solar cells.

Currently we are using this material for another promising environmental application; namely, detoxification of water. The basic principle is the following: light-generated excitons in these systems can be split in order to kick-start a set of electron-transfer reactions in polluted waters, within which these photocatalysts are dispersed. The elctron-transfer reactions, if carefully directed, can result in complete oxidation of the toxic organic poisons in the polluted water, which in turn should help in the detoxification of water. In this case, the semiconductor is called a photocatalyst, since it uses light and facilitates oxidation of toxic organic wastes, without getting modified during the detoxification process.

We have achieved this, using semiconductor nanoparticles that were made using soft-chemical routes (<60 degrees C). In fact our most efficient "photocatalyst" is made at room temperature, without the aid of any furnace or oven! This essentially means that we have a photocatalyst which can be made at very low cost, and with very little carbon foot-print (which means minimum pollution). In addition, these nanoparticles are expected to be environmentally benign and biologically inert, since they belong to the size-regime where these particles are known to be non-toxic. Further more, we have developed synthetic paradigms and rules for photocatalyst design, the combination of which is expected to be helpful in making photocatalysts viable for use in the developing world.

In order to know the details of our work, please feel free to talk to me.

Ref: This work has been communicated, and should be in print soon.