Daniel Lincot appointed to the Chair in Technological Innovation at Collège de France

Your lectures at Collège de France will focus on photovoltaic solar energy and the energy transition. What message do you want to convey?

The opportunity to teach at Collège de France will allow me to present the latest scientific and industrial advances in photovoltaic conversion of solar energy. They open up radically new ways for its large-scale use. Virtually unlimited and renewable, it raises many hopes in the fight against climate change.  I would also like to respond to certain critics who tend to minimise its interest because of its 'intermittency' or 'dilution', or who claim that solar cells require the use of rare earths, are not recyclable, or barely pay for the grey energy needed to manufacture them. I want to provide quantitative and up-to-date information, without denying the questions that arise for large-scale development. And it is not only a question of evoking the technological side but also the social, economic and of course ecological stakes.

Since the 2000s, the deployment of photovoltaic energy has been growing rapidly and is accelerating today. What was the state of progress when you started research in the 1970s?

The photovoltaic effect, i.e. the fact that light is able to generate electricity when it shines on certain materials, was discovered at the beginning of the 19th century by a French scientist, Edmond Becquerel, whose 200th birthday we have just celebrated. It was not until 1954 and silicon cell technology that conversion efficiency took off at 6% and then 13%. The technology was immediately transferred to the nascent space industry. However, the costs were too high for other applications. In the 1970s, solar energy was mainly represented by thermal and concentrated solar power. On the advice of Michel Rodot, a polytechnician and designer of the first French silicon photovoltaic cells, I chose to do a thesis on photovoltaics.  With the 1973 oil crisis, there was a spotlight on solar energy, a sort of collective dream: perhaps we could use this abundant energy as an alternative to oil. But the time was not yet ripe, given the development of nuclear energy and the fall in oil prices.

Now that photovoltaics has taken off, benefiting from a general drop in costs, what are the main technologies in this sector?

There are many materials that can be used to make photovoltaic cells, both inorganic and organic, and even molecular, and we only know the tip of the iceberg. It is an extraordinary scientific field, driven by fundamental research, which I will present during my lectures. In practice, the vast majority (95%) of photovoltaic panels are made of crystalline silicon and have a commercial yield of around 20%. But there are also so-called "thin-film" technologies, such as the CIGS cells (based on copper, indium, gallium and selenium) on which I am working.They have slightly lower yields and are still a little more expensive, but have great strategic potential. In 2009, exceptional materials also emerged, which deviate from the traditional canons of semiconductor materials, halogenated hybrid perovskites, whose efficiency is increasing rapidly.  Today, a particularly ambitious objective, supported in particular by Institut photovoltaïque d'Île-de-France (IPVF*), is to converge photovoltaic technologies to create "multi-junction" solar cells combining silicon and thin films and to achieve very high efficiencies (the record for all categories is currently 46.7%!).I am dreaming of a "diagonal of the century" as a goal: in 2020, commercial photovoltaic modules have an efficiency of 20% with a single junction, we should aim for 30% in 2030 with two junctions, 40% in 2040, and perhaps even 50% in 2050.  There is a way to go, but I am already surprised at the place solar energy has taken today, defying all the forecasts of the International Energy Agency as shown in this 2015 MIT report. There is reason to be optimistic, especially with the progress made in storage and hydrogen technologies.

*IPVF: a joint research unit CNRS, École Polytechnique - Institut Polytechnique de Paris, Chimie Paristech-PSL, IPVF SAS