A team of researchers led by the Korea Institute of Materials Science (KIMS) has developed a new optical technology for coloring flexible thin-film building-integrated (BIPV) and vehicle-integrated (VIPV) solar panels.
The proposed technology is reported to be able to exhibit different reflection colors without significantly reducing the efficiency of solar cells. We directly fabricated the cells using transparent electrodes based on aluminum hydride-doped zinc oxide (AZO) materials and silicon films," study lead author Jung-dae Kwon told PV Magazine.
The scientists also designed a multilayer film with a refractive index difference of less than 5%, which they claim minimizes reflection losses in the visible region of light absorbed by the solar cell. "It can be applied to a variety of thin-film solar cells because it hardly degrades the solar cell efficiency due to color implementation," they explain.
In the paper "Flexible multi-layered coloring transparent electrode composed of AZO–based materials," published in the Chemical Engineering Journal, the researchers explain that the hydrogenation of azo leads to the passivation of oxygen and zinc vacancies, strengthening the oxygen and hydrogen bonds, thereby providing the required electrical and optical properties.
They tested their method on thin-film cells based on amorphous silicon (a-Si). To achieve all three primary colors, the team fabricated distributed Bragg reflector (DBR) electrodes made of six pairs of AZO and AZO:H on ultrathin colorless polyimide using conventional vacuum sputtering deposition.
DBR consists of alternating dielectric layers, often used as reflectors and dielectric mirrors, with its multilayer composition alternating between high and low refractive index, resulting in a customizable reflection spectrum.
The team highlighted its ability to control color and conductivity through the thickness of the DBR layer, saying there was little difference in conversion efficiency for each color, with excellent flexibility and durability under bending stress. The green prototype performed best, with a conversion efficiency of 5.45%. Prototypes in all three colors were subjected to 600 cycles at a bending radius of 6 mm. Blue, green, and red are rated at 1.14 W, 1.29 W, and 1.22 W per gram, respectively.