The quest for alternative fuels has become one of science’s major pre-occupations and finding ways to cheaply produce energy from the sun is a key battlefront. Researchers at Berkeley, California, have found a way to make cheaper, better solar cells using tiny nanopillar semiconductors measuring just billionths of a meter wide. The underlying theory is that a 3-D solar cell has more surface – and, therefore, will be a much more efficient light-collector – than the usual 2-D solar cell.
The idea of achieving this by growing photovoltaic crystals isn’t new – we reported on nano flakes back in 2007 – but making them cheaply, efficiently and with consistent density and dimensions has proved disappointingly difficult.
The Berkeley team overcame this with a two-stage process. First they grew pillars of cadmium sulfide on an aluminum foil template. Then they embedded the nanopillars in clear cadmium telluride, which provides a “window” to catch the light.
In contact with each other, the two materials form a solar cell, with charge-carrying electrons flowing down to the aluminum, and the “holes” (the absence of an electron) conducted to a thin copper-gold electrode on the surface of the window. Initial tests measured an efficiency of six percent that – while not quite at the 10 to 18 per cent range of mass-produced commercial cells – is one of the best for a nanostructured material. And, given that the non-transparent electrode on top reduced efficiency by 50 per cent, there’s a lot of room for improvement.
Apart from using very cheap materials, this process also easily lends itself to practical adaptations. The researchers were able to make a flexible version of the same design – by replacing the aluminum with indium and embedding the whole thing in soft plastic – with almost no loss of performance.
A combined effort by the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and the University of California, the work is still at an early stage. But they’ve got the theory now and believe that, in the long term, this process could produce solar cells at a tenth of the cost of crystalline silicon panels.