Monograin layer solar cell with 6.4% efficiency

Scientists at Estonia’s Tallinn University of Technology (TalTech) have developed a monograin layer solar cell based on a semiconductor compound made of microcrystalline powders that is known under the chemical formula Cu₂CdGe(S_xSe_1-x)₄.

The cell was fabricated with a very tiny absorber based on monograin powders that are 10-30μm thick, which the researchers said compares to absorbers made of silicon that are generally 150-200μm thick. “A solar cell absorber should be able to absorb light as efficiently as possible, in particular to harness the full spectrum of wavelengths in solar radiation,” the researchers explained. “In addition, the absorption coefficient of the absorber material must be as high as possible, which means that, already, a very thin layer of the absorber should absorb all the incident light.”

The powders were synthesized by molten salt method in quartz ampoules in a special chamber furnace, which the Estonian group describes as a low-cost manufacturing step. “I don’t have very precise cost calculations at the moment but definitely it will be lower than conventional thin-film production because this technology doesn’t have to use high-vacuum systems,” researcher Marit Kauk-Kuusik told pv magazine. “In the future, all layers and components will be done with vacuum-free technology.”

The microcrystals obtained through this process form, then, miniature, lightweight, flexible, and semi-transparent solar cells in a large module. The device showed an efficiency of 6.4%, which the academics said is the highest efficiency ever recorded for Cu₂CdGe(S_xSe_1-x)₄-based solar cells. It was described in the study The effect of S/Se ratio on the properties of Cu₂CdGe(S_xSe_1-x)₄ microcrystalline powders for photovoltaic applications, published in Solar Energy.

In 2019, the same research group built a kesterite solar cell with 8.7% efficiency.