(December 8, 2015) Solar
cells are generally flat. However, by adding minuscule silicon pillars to the
surface, it is possible to more than double the amount of energy produced for
each surface. This has been demonstrated by research by academics at the
University of Twente research institute MESA+. In an article published last
week in the scientific journal Advanced Energy Materials, they show what the
optimum height and doping depth of the pillars is.
Last year, the University of Twente researchers succeeded in
creating a semi-conductor fitted with one million minuscule pillars per square
centimetre. These pillars are able to convert sunlight into electricity. The
semi-conductor consists of two types of silicon: one is ‘contaminated’ with the
element boron and the other with phosphorus. The transition between both types
of silicon, known as the PN junction, is essential for the efficiency of the
solar cell, as it is at this location in the structure that the positive and
negative charges are separated. The challenge in creating the pillars was to
make sure that the PN junction followed the structure of the surface as
accurately as possible.
DOUBLING EFFICIENCY
In a new study, the same researchers looked at what pillar
height and what PN junction depth the semi-conductor works most efficiently.
The answer was 40 micrometres high and 790 nanometres deep, producing an
efficiency rate of 13 per cent. This represents more than double the efficiency
compared to a flat structure, where no more than six per cent of the sunlight
can be converted into electricity.