Toshiba Corp achieved a power generation efficiency of 23.8% with a tandem-type solar cell using transmissive cuprous oxide (Cu2O).
The efficiency is higher than the power generation efficiency of crystalline silicon (Si) solar cells, which are widely used. Cu2O is a copper oxide that is abundantly available on the earth and, therefore, expected to lower costs. Toshiba made this announcement June 18, 2019.
The power generation efficiency of a tandem-type solar cell is improved by combining solar cells having different properties as top and bottom cells and generating power by using both of the cells.
Thus far, tandem-type solar cells that use gallium arsenide semiconductor, etc and have a power generation efficiency of 30-40% have been commercialized. However, their production cost is several hundred to several thousand times higher than that of crystalline Si solar cells.
In January 2019, Toshiba succeeded in making a transparent cell using Cu2O and developed a tandem-type solar cell using a transmissive Cu2O solar cell as a top cell. The transmissive Cu2O solar cell generates power by absorbing short-wavelength light and transmits about 80% of long-wavelength light. The power generation efficiencies of the top cell, bottom cell and the entire device were 4.4%, 17.6% and 22%, respectively, which is almost the same as that of crystalline Si solar cells.
This time, to improve power generation efficiency, Toshiba applied a new n-type oxide semiconductor material to the transmissive Cu2O solar cell and reduced the potential difference at the interface between the Cu2O thin film (p layer) and n layer.
It is possible to realize an even higher power generation efficiency by further optimizing the n layer and reducing energy loss, Toshiba said. The company plans to advance the research and development in the aim of realizing an efficiency of 30-40% after three years.