Can photovoltaics scale fast enough to make a significant difference to the environment as a green energy source? This was a question posed by Raffi Garabedian, CTO of First Solar, during a panel discussion on 'green photonics' and solar energy taking place at Photonics West yesterday in San Francisco.

Whether photovoltaics can make a difference as a green energy source is unclear, according to Garabedian – for instance, it was pointed out by the panel moderator, Stephen Eglash, the executive director of the Energy and Environment Affiliates Program at Stanford University, that while China might be investing heavily in solar power, it is also investing in coal power stations to meet its energy needs. Homer Antoniadis, the global technology director at DuPont Photovoltaic Solutions, added that in India, the price of solar panels is too high for the country to adopt solar power fast enough to make a difference to its carbon emissions.

The overriding message from the panellists, and what they're all aiming for, is higher efficiencies. Antoniadis noted that, because the cost of installing solar panels is so high, the efficiencies have to be improved substantially to make a difference to the overall cost of solar energy.

At the moment, according to Antoniadis, crystalline silicon panels with relatively low efficiencies of around 15 per cent make up the majority of photovoltaics active today, and he stated that crystalline silicon will be the dominant class of solar cell over the next five years. However, he added that other photovoltaic technologies will have a role and will operate alongside crystalline silicon. Cadmium telluride, it was noted, is extremely cheap to produce and is therefore excellent for large-scale installations. Garabedian commented that there isn't going to be one single product that will meet the world's photovoltaic needs.

One of the more exciting areas of research touched upon during the discussion was perovskite solar cells, an area with huge potential which has grown from the first scientific paper published only 18 months ago, to now a large number of groups working on the material.

The properties of perovskite mean the material can be stacked on top of silicon. The material has a particular crystal structure, which allows electrons and holes to travel through thicker solar cells that absorb more light and therefore generate more electricity.

The current efficiency record for a perovskite solar cell is 15 per cent. Antoniadis said perovskites represent a huge opportunity for the solar industry, but that reliability is a constraint with the material and there is an issue with producing it cost-effectively.

Lifetime of solar panels was also noted as an important factor for the uptake of photovoltaics – panels would have to last 25 years or more to make them suitable for installing on buildings.

So, what kind of efficiencies is the industry aiming for? Martin Green, a professor at the University of New South Wales in Australia, believes that 40 per cent with unfocussed sunlight is achievable, but that is quite a long way off in the future, he said. There are other factors, such as cost of manufacture and reliability, that come into play, but higher efficiencies would make photovoltaics a much more attractive energy source and one that can make more of a difference in curbing climate change.