Toshiba Corp achieved a conversion efficiency of 23.8% with a tandem-type photovoltaic (PV) cell that uses cuprous oxide (Cu2O), etc for the top cell and crystalline silicon (Si) for the bottom cell.

This was announced June 18, 2019. Toshiba plans to increase the efficiency to 30% or higher in about 2022 for commercialization. The cell might become a new PV cell that realizes both a low cost and high efficiency.

The top cell of the tandem-type PV cell developed by Toshiba. It measures 25 x 25mm. (source: Toshiba)

This time, Toshiba developed a two-story PV cell called "tandem type." With the two-story structure, it might become possible to convert sunlight into electricity more efficiently. The company achieved the conversion efficiency of 23.8% by using (1) a crystalline Si PV cell with a conversion efficiency of 22% for the first floor (bottom cell) and (2) a PV cell consisting of Cu2O (p-type semiconductor) and n-type oxide semiconductor for the second floor (top cell).

An overview of the tandem-type PV cell

Toshiba announced almost the same tandem-type PV cell in January 2019, but its conversion efficiency was 22%. The efficiency was equivalent to that of the crystalline Si PV cell used for the bottom cell, and there was no advantage in making a tandem type. This time, the efficiency of the new PV cell is 1.8 points higher than the efficiency of the bottom cell, proving the value of the tandem type, the company said.

Problem of n-type semiconductor improved

According to Toshiba, the reason why the conversion efficiency increased by 1.8 points in less than six months is that the company employed a new n-type oxide semiconductor material for the top cell.

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