A study on multi-junction silicon thin film solar cells employing n doped SiO:H-based and modified a-Si:H-based layers

Abstract

Si based materials are several advantages for thin films solar cells: adjustable band gap, well-developed fabrication techniques, multi-junction device capability-which maximized the utilization of the solar spectrum. But the limitation of low absorption coefficient of Si based materials, the researches of optimization of intrinsic layer and efficient light trapping are critical in the field of thin-film silicon solar cells for a high efficiency, low cost and enhancement of stability of device. In this thesis, I optimized a-Si:H and a-SiGe:H layer for top and middle cells in multi-junction thin film solar cells, and prepared n-uc-SiO:H layers for interlayer of multi-junction dells and back reflector for uc-Si:H bottom cells. Chapter 1 introduces basic knowledge in thin film solar cell that includes the electrical optical properties of intrinsic layers, characterization tools for solar cells. Chapter 2-5 shows experimental results for this dissertation. In Chapter 2, we have optimized the top cell performance by lowing a band-gap of intrinsic layer and introducing intrinsic buffer layer for the high efficiency of tandem sola cell. The intrinsic buffer layer improved not only Voc (from 0.87V to 0.89V) but also Jsc (10.8 mA/cm2 to 11.82 mA/cm2) compared the without buffer layer. By further optimization of the p-layer thickness, we could achieve the initial conversion efficiency of 7.81 % with Jsc of 11.91 mA/cm2 in the thickness of intrinsic absorb layer of 250nm. With this result, we try to achieve higher conversion efficiency of tandem solar cell with the proper current matching condition In chapter 3, we have improved the tandem cell performance by introducing n-uc-SiO:H interlayer and optimized top cell. The n-uc-SiO:H interlayer is investigated on electrical structural measurements. The n-uc-SiO:H of conductivity - 10-3S/cm was used in tandem solar cell as an interlayer and we confirmed the conductivity of 10-5S/cm is available as the interlayer. We achieve...