Photovoltaic cells: sulfur and tin have the same efficiency as monocrystalline silicon

A group of researchers from Tokyo University, led by professor Issei Suzuki of the Institute of Multidisciplinary Research for Advanced Materials, has found a way to make tin sulphide (SnS) competitive with silicon, also from the point of view of efficiency.

Tin sulfide is a compound obtained from sulfur and tin with interesting photovoltaic properties which have always captured the attention of scientists.

Thanks to’high optical absorption coefficient and a mid-range direct bandgap of 1.3-1.4 eV, theoretically, tin sulphide could provide cells with a solar radiation/electricity conversion efficiency equal to 32%.

A record value that makes the sulfide direct competitor of monocrystalline silicon.

This data is not new; the material it has been tested several times, even revealing its Achilles heelwhich makes it difficult to market as a viable alternative to silicon.

The SnS fails to get a no-load voltage high enough to make the solar cell in which it is present highly efficient; the value of tin sulphide, in fact, is equal to, or even lower than, at 5%, less than half of the solar cells currently on the market.

Researchers have tried different ways to overcome the limitation of sulfide, due to a phenomenon called “freezing effect of Fermi levels”and now the Japanese team seems to have found the right strategy.

The team added molybdenum oxide, an industrial catalyst, to the SnS crystals.

X-ray photoelectron spectroscopy analysis showed that, in this way, the Fermi energy of SnS is able to move across the entire band gap, increasing the no-load voltage.

The results of this research have been published in The Journal of Physical Chemistry C.

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