Transparent crystalline silicon solar cells

Abstract

Solar cells have attracted considerable attention as an emission-free, eco-friendly alternative energy source owing to an impending global environmental and energy crisis. However, commercialized solar cells have limited applicability because they are rigid and opaque. Hence, research on solar cells with added functionalities, such as flexible and transparent solar cells, are actively being conducted. Transparent solar cells are novel devices that combine solar energy conversion and visible transparency. Transparent solar cells are gaining more popularity as they are applicable in various areas, including building-integrated photovoltaics and glass for vehicles. Up to now, transparent solar cells are developed mainly focusing on organic solar cells and dye-sensitized solar cells. Most of the polymers and dyes used in organic solar cells and dye-sensitized solar cells can be fabricated to thin-film easily via a solution process such as spin coating. And, the thin film has light transparency. Therefore, many studies are being conducted on transparent solar cells based on thin films utilizing this property. However, solar cells based on organic materials still have challenging problems such as low stability in moisture and other environmental conditions. Furthermore, they have shown specific hue because the polymers or dyes have their color. Crystalline silicon solar cells have high power conversion efficiency (up to 26.7%) and high stability (lifetime over 20 years) compared to other types of solar cells, and the materials required for fabricating them are also abundant (silicon is the second abundant material in Earth). Therefore, crystalline silicon solar cells currently occupy more than 90% of the solar cell market. Despite the advantages of the crystalline silicon solar cells, the opaque nature of the crystalline silicon wafer, which is a primary material of crystalline silicon solar cells, makes the development of transparent solar cells using crystalline silicon challenging. Firstly, in this thesis, I will explain the development of transparent crystalline silicon substrate, which is the basic material to develop the crystalline silicon solar cells. Transparent crystalline silicon substrate was developed by establishing micro-sized light transmission windows to a 200-µm thick crystalline silicon wafer known to be opaque. The windows were formed to enable the penetration of visible range. Therefore, the substrate shows a neutral color. Furthermore, the gap between the light transmission windows was chosen using the minimum angle of resolution. Therefore, in the case of the human, each light transmission windows are invisible. Light absorption regions were formed on the transparent crystalline silicon substrate to absorb incident light efficiently. Secondly, I will discuss how to fabricate crystalline silicon-based transparent solar cells using the developed colorless glass-like silicon substrate. The photovoltaic performance of the transparent crystalline silicon solar cells is much higher than that of other types reported colorless transparent solar cells until now. Thus, the developed transparent crystalline silicon solar cells are the best choice for the development of the emerging transparent solar cells that will satisfy high power conversion efficiency as well as high stability and neutral colors such as glass. Furthermore, we believe that the research results of this thesis would contribute to developing next-generation solar cells, especially transparent solar cells. In addition, this study makes an important contribution to the fields of solar cells as well as other transparent electronics.