Engineering news
Researchers have discovered a greener, low-cost alternative to manufacturing solar cells based on a new nanocrystal material.
The research, led by Professor Gerasimos Konstantatos at the Spanish Insitute of Photonic Sciences (ICFO), aimed to find an alternative to the common silicon inorganic solar cell. Many existing alternatives, including lower-cost thin film solar cells, contain toxic elements such as lead or cadmium, or contain scarce elements such as indium or tellurium.
The ICFO researchers fabricated a 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.
The crystals were shown to be very strong panchromatic absorbers of light – sensitive to all visible colours of the spectrum - and act as an effective charge-transporting medium for solution-processed solar cells.
Dr. Maria Bernechea, a researcher on the project, said: "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 synthesised at very low temperatures of 100ºC, an order of magnitude lower than the ones required for silicon based solar cells."
The researchers developed the cells through a hot-injection synthetic procedure. They first dispersed the nanocrystals into organic solvents, where the solutions showed to be stable for months without any losses in the device performance.
The nanocrystals were then deposited onto a thin film of zinc oxide (ZnO) and indium tin oxide (ITO), the most commonly used transparent conductive oxide, through a layer-by-layer deposition process until a thickness of approximately 35nm was achieved.
Researcher on the project, Dr Miller, said: "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."
The cells have achieved power conversion efficiencies of 6.3%, which is on par with the early reported efficiencies of currently high performance thin film PV technologies.
The ICFO said this highlights 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.
Konstantatos said: "This is the first efficient inorganic nanocrystal solid-state solar cell material that simultaneously meets demands for non-toxicity, abundance and low-temperature solution processing. These first results are very encouraging, yet this is still the beginning and we are currently working on our next milestone towards efficiencies more than 12%".