Inorganic solar cells promise greener, lower-cost silicon alternative
The solution-processed, semi-transparent solar cell is based on AgBiS2 nanocrystals that can be produced in ambient conditions at low temperatures. These crystals have shown to be very strong absorbers of light across a wide spectrum and have been further engineered to act as effective charge-transporting medium for solution-processed solar cells.
“They contain AgBiS2 nanocrystals, a new material based on non-toxic elements and the chemical synthesis of the nanocrystals allows control of their properties through engineering at the nanoscale and enables their dissolution in colloidal solutions,” said Dr Maria Bernechea. “The material is synthesized at very low temperatures, an order of magnitude lower than the ones required for silicon based solar cells.”
The first 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, and the team is looking to double this to over 12%. 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.
The team of researchers at ICFO developed these cells through a low temperature (100ºC) 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. Then, the nanocrystals were deposited onto a thin film of ZnO and ITO transparent conductive oxide, through a layer-by-layer deposition process until a thickness of approximately 35nm was achieved.
“A very interesting feature of the 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. This gives AgBiS2 solar cells significant potential as a low-cost alternative to traditional solar cells,” said another member of the team, Dr Nicky Miller.
“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,” said team leader Prof Gerasimos Konstantatos. “These first results are very encouraging, yet this is still the beginning and we are currently working on our next milestone towards efficiencies over 12%”.
The research was part of the NANOMATCELL European project to move from silicon cells to low-cost environmentally friendly solar cells. For more, see the paper “Solution-processed solar cells based on environmentally friendly AgBiS2 nanocrystals.”
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