An alternative to silicon solar cells for safer green tech

As the world searches for cleaner ways to produce energy, solar energy comes to mind as one of the most popular alternatives. However, the pace at which the world is consuming energy requires more efficient green tech that can be applied to buildings, clothing, consumer electronics, wearables, and more.

This requires the use of ultra-thin film, low-cost and ideally flexible solar cells that can be used without compromising the environment during production, use, or disposal.

The most common inorganic solar cells, like the ones on roof tops and in solar farms, are made of silicon. The production of silicon solar cells can be expensive and energy demanding and the final modules are heavy and bulky. Many silicon alternatives that are lower-cost  and also thin film, are composed of toxic elements like lead or cadmium, or contain scarce elements such as indium or tellurium.

That’s why researchers are on a hunt for a safer and more efficient green-tech alternative.

Researchers from ICFO- The Institute for Photonic Sciences have developed a solution. They created a solution-processed, semi-transparent solar cell based on AgBiS2 nanocrystals, a material that consists of non-toxic, earth-abundant elements, produced in ambient conditions at low temperatures. These crystals have shown to be very strong panchromatic absorbers of light and have been further engineered to act as effective charge-transporting medium for solution-processed solar cells.

“They contain AgBiS2 nanocrystals, a novel material based on non-toxic elements. The chemical synthesis of the nanocrystals allows exquisite control of their properties through engineering at the nanoscale and enables their dissolution in colloidal solutions. The material is synthesized at very low temperatures (100ºC), an order of magnitude lower than the ones required for silicon based solar cells,” said Dr. Maria Bernechea, a researcher on the team.

The ICFO team developed these cells through a low temperature hot-injection synthetic process. They dispersed the nanocrystals into organic solvents, where the solutions showed to be stable for months without any losses in the device performance. Then, they deposited the nanocrystals onto a thin film of ZnO and ITO, the most commonly used transparent conductive oxide, through a layer-by-layer process until achieving a thickness of approximately 35 nm.

“A very interesting feature of AgBiS2 solar cells is that they can be made in air at low temperatures using low-cost solution processing techniques without the need for the sophisticated and expensive equipment required to fabricate many other solar cells. These features give AgBiS2 solar cells significant potential as a low-cost alternative to traditional solar cells.” said Dr. Nicky Miller, also on the team.

The team reports that these cells have already achieved power conversion efficiencies of 6.3%, which is on par with the early results of high performance thin film PV technologies. This signifies that the potential of AgBiS2 as a solar-cell material that in the near future can compete with current thin film technologies that rely on vacuum-based, high-temperature manufacturing processes.

Though there is still work to be done, with the team hoping to achieve a next milestone of 12% efficiency, the results indicate a turning point in the production of solar cells — moving away from silicon to more low-cost, environmentally friendly versions that will make the world safer and more sustainable