Sharp's activities in photovoltaics have recently provided the company with two pieces of good news. The first is that its research labs in Japan have fabricated a triple-junction solar cell with a record-breaking power conversion efficiency of 35.8% — the highest value reported for any cell illuminated with unconcentrated sunlight. The second is that a solar-powered vehicle covered with Sharp's compound solar cells triumphed in the Global Green Challenge solar-car race across Australia at the end of October. The 3,000-km race from Darwin to Adelaide was won by a team from Tokai University in Japan. Their 'Tokai Challenger' vehicle completed the course with an average speed of approximately 100 km h−1.

Credit: Global Green Challenge

Sharp's record-breaking 35.8%-efficiency cells consist of three vertically stacked p–n junctions that are each made from a different compound semiconductor (the top, middle and bottom layers are InGaP, GaAs and InGaAs, respectively). Each junction is designed to absorb light at a different wavelength band of the solar spectrum, which maximizes power generation. Such multijunction cells have been a popular design for many years and are often used in space to help power satellites, and in solar farms, which use reflectors to concentrate the intensity of sunlight. Indeed, when used with concentrated sunlight, triple-junction cells — developed independently at Sharp, the Fraunhofer Institute for Solar Energy in Germany and the US firm Spectrolab — all achieved efficiencies of over 40%, but this figure is usually much lower for unconcentrated sunlight.

According to Sharp, the key to achieving these latest results for unconcentrated light was to form the bottom junction of the cell from InGaAs rather than germanium — a challenge only recently solved through considerable improvements in semiconductor fabrication technology. The research that enabled this development took place under a solar-cell initiative organized by Japan's New Energy and Industrial Technology Development Organization.

Unfortunately, it was not all good news in October for Sharp. The firm's biannual business results for the six months ending 30 September 2009 showed a year-on-year drop of 17.5% in net sales to 1,288 billion yen. Worse still, operating income declined 96.9% from 50.8 billion yen in 2008 to 1.5 billion yen in 2009 for the same biannual period, only narrowly avoiding a net loss. Sales of LCDs (down 33%) and other electronic items (down 27%) were particularly hard hit owing to the global recession, but the firm saw sales rise from June onwards and is now benefiting from a cost-reduction programme that it implemented earlier in the year.