From the photovoltaic effect to photoelectric cells

The Industrial Revolution changed the world - not just the economy, but also our everyday lives. The growing use of alternative energies is changing the world in the same way. Whether we call it the green revolution, the ecological transition, the use of alternative energy sources or the direction of history, it doesn't change the fact that we've entered a new world.

Energy consumption has risen faster than population growth over the last forty years, and this trend is set to accelerate in the first half of the 21st century due to growth in China and India. Two solutions exist: moderation of consumption and the use of new energy sources.

These alternative energy sources must, however, meet a new imperative: they must not contribute to global warming. Nuclear power is generally distinguished from other energy sources: wind, biomass, hydraulic, solar (thermal and photovoltaic) and geothermal.

Photovoltaics is one of these alternative energy sources, and despite its modest contribution to date, it is set to become one of the major energy sources of the future. Photovoltaic energy has already achieved a number of major successes. Without photovoltaic energy, there would be no International Space Station, and no Spirit or Opportunity rovers on Mars.

But the photovoltaic energy sector is also a high-tech business, changing rapidly in a high-growth market and requiring, in addition to strong scientific and technical skills, consideration of legislative, political and societal aspects. It therefore represents a fantastic field of opportunity for 21st century engineers.

In order to make a significant contribution to its development, we need to start from the source of this energy, the Sun, and consider the factors determining the corresponding ground potential. This is the subject of the first part of this article. This energy must then be converted into electricity using a photovoltaic cell.

The second part will therefore be devoted to the study of the photovoltaic cell, the heart of the conversion device. To understand how this conversion works and the parameters governing its performance, we'll start with a review of semiconductor physics. We'll then look at the absorption of light by a semiconductor and the photovoltaic conversion provided by a pn junction. Information will then be given on the materials that make up these pn junctions in photovoltaic devices; on silicon, of course, but also on less commonly used materials, in both bulk and thin-film form. This second part concludes with a look at technologies for the various elements that make up a photovoltaic cell, in addition to the pn junction.

The third part will be devoted to changes of...