(A) study on color-controlled semi-transparent and flexible organic solar cells

Abstract

As energy consumption around the world increases exponentially, and environmental issues are emerging, research into alternative energy sources is being actively conducted. In particular, the organic solar cell has been attracting attention as one of the solar cell technology, having a low cost, flexibility, semitransparent characteristics. However, semitransparent organic solar cells (ST-OSCs) don’t absorb light as much as they are transparent, so ST-OSCs always show trade-off relationship between transmittance and efficiency. In addition, since organic materials are vulnerable to oxygen and moisture, an encapsulation structure that prevents oxygen and moisture is essential. In this study, the encapsulation structure, which is essential for organic solar cells, was used to increase the efficiency while controlling the transmittance of the ST-OSCs.To make color control film (CC-barrier foil), low and high refractive index layers were deposited on the encapsulation film to form a 1-D photonic crystal, which can be designed to reflect the desired wavelength band and transmit the remaining wavelength bands depending on the thickness of each layer. It was. Designed to reflect R, G, and B, respectively, and to make the color adjustment layer with the maximum transmission of 550nm to make it look brightest to human eyes. When the color control film is applied to the upper layer of the semi-transparent organic solar cell, the light in high reflectance region is reflected again to increase the efficiency, and the light in high transmission region is preserved by transmitting the light.To realize the flexibility, which is an advantage of the organic solar cell, CC-barrier foil was applied to the flexible substrate to have a wide form factor. Among the materials constituting the 1-D photonic crystal, ZnS and LiF, in particular, LiF, when applied to a flexible substrate, exhibited physically brittle characteristics, thereby replacing the low refractive index material with BmPyPb, an organic material, to produce a color control film. Through this, the flexible color control film could be applied to the flexible ST-OSCs to produce high efficiency and high transmittance, and the reliability and bending test showed that the mechanical properties were better when the encapsulation structure was obtained. In addition, a metal cavity structure using Al$_2$O$_3$ was used to improve the barrier properties of the CC-barrier foil. As the thickness of Al$_2$O$_3$ is changed, color control of CC-barrier foil was simply done, and by applying to ST-OSCs, it could retain 91.5% of the initial efficiency for more than 30 days even in an accelerated environment(27°C, 90% RH) proving excellent barrier property. This study is expected to be an example to show how to increase the reliability and efficiency of ST-OSCs practically.