Toshiba has achieved a significant milestone in photovoltaic technology by reaching a twenty-six point six percent conversion efficiency using a tandem solar cell that incorporates copper(I) oxide. Copper(I) oxide is a highly promising material for top cells due to its wide bandgap of two point one seven electron volts. This wide bandgap allows it to absorb shorter wavelengths of light efficiently, while leaving the rest of the spectrum for the bottom cell. To reach the ultimate commercial goal of thirty percent efficiency, researchers estimate that the top cell needs to achieve twelve to thirteen percent efficiency, while the bottom cell must deliver seventeen to eighteen percent efficiency.
A major technical challenge in this development was the increase in interface reflection within the multilayer film structure. Through detailed simulations, Toshiba engineers discovered that this high reflection was caused by the low refractive index of the original n-type layer. To address this issue, they introduced titanium dioxide, a material known for its high refractive index, into the n-type layer. This innovative adjustment successfully reduced light reflection in the wavelength range around five hundred nanometers. As a result, Toshiba demonstrated that it is possible to achieve both high efficiency and high transmittance in the top cell simultaneously, all while maintaining the core power generation characteristics. This breakthrough opens up new possibilities for flexible, high-efficiency solar integration on electric vehicles and building facades.
