Silicon solar cells have proven to be a superior photovoltaic technology, as they use raw materials abundantly available on the Earth and perform with high efficiency. However, silicon solar cells are based on rigid, thick, heavy wafers and can therefore be installed only in a limited number of places.
The use of thin membranes is one of the ways to overcome this disadvantage. This will reduce the silicon concentration by more than 99% to save raw materials dramatically, and to make cells lightweight and flexible.
Consequently, the cells can easily be integrated into buildings, urban architecture, and even small everyday devices. The problem is that thin silicon membranes is unable to absorb light as efficiently. In fact, it absorbs only 25% of sunlight and can even see through them.
The use of a new rationally designed nanostructure texture led researchers at Surrey University, AMOLF, and Imperial College have discovered a way to fabricate thin photovoltaic cells opaque, and thus improve their efficiency.
In laboratory experiments, researchers found that textured thin membranes absorb 65% sunlight, which is as close to the ultimate theoretical absorption limit of nearly 70%. This absorption capacity is the highest ever demonstrated in such a thin silicon membrane, and is therefore likely that light-weight, flexible, and efficient silicon photovoltaic cells will be fabricated in the near time.
In terms of functioning, the patterned nanostructure judiciously redirects straight sunlight at several angles, and thereby traps light inside the silicon membrane.
With the trapping of light, this has more chances to be absorbed and the thickness of the membrane increases effectively for light.
The understanding of angles that will trap photons inside the silicon membrane enabled researchers to design their nanopattern based on a state of matter often found in nature.