Optical Analysis of a ZnO/Cu<sub>2</sub>O Subcell in a Silicon-Based Tandem Heterojunction Solar Cell

• 作者: ?rnulf Nordseth Bengt Gunnar Svensson Cristina Vasiliu Dan Cr?ciunescu Dan Savastru Edouard Monakhov Florin Dr?gan Halvard Haug Irinela Chilibon Kristin Bergum Lauren?iu Fara Laurentiu Baschir Paul Sterian Raj Kumar Sean Erik Foss
• 来源期刊: 绿色与可持续化学(英文)
• 学科: 物理学
• 关键词: TANDEM Solar Cells HETEROJUNCTION Cuprous Oxide Magnetron Sputtering OPTICAL Properties OPTICAL Modelling
• 年，卷（期）: 2017,（1）
• 页码范围: 57-69
• 页数: 13页
• 分类号: O4

摘要

Research on silicon-based tandem heterojunction solar cells (STHSC) incorporating metal oxides is one of the main directions for development of high-efficiency solar cells. In this work, the optical characteristics of a STHSC consisting of a ZnO/Cu2O subcell on top of a silicon-based subcell were studied by optical modelling. Cu2O is a direct-gap p-type semiconductor which is attractive for application in solar cells due to its high absorptance of ultra-violet and visible light, nontoxicity, and low-cost producibility. Highly Al-doped ZnO and undoped Cu2O thin films were prepared on quartz substrates by magnetron sputter deposition. Thermal annealing of the Cu2O layer at 900°C enhances the electrical properties and reduces optical absorption, presumably as a result of increased grain size. Hall effect measurements show that the majority carrier (hole) mobility increases from 10 to 50 cm2/V×s and the resistivity decreases from 560 to 200 Ω×cm after annealing. A Cu2O absorber layer of 2 μm thickness will generate about 10 mA/cm2 of photocurrent under AM1.5G illumination. The optical analysis of the STHSC involved calculating the spectral curves for absorptance, transmittance, and reflectance for different thicknesses of the thin film layers constituting the ZnO/Cu2O subcell. The complex refractive indices of the thin films were derived from spectroscopic ellipsometry measurements and implemented in the simulation model. The lowest reflectance and highest transmittance for the ZnO/Cu2O subcell are obtained for a thickness of approximately 80 nm for both the top and bottom AZO layers. The SiNx anti-reflection coating for the c-Si bottom subcell must be optimized to accommodate the shift of the photon spectrum towards longer wavelengths. By increasing the thickness of the SiNx layer from 80 nm to 120 nm, the total reflectance for the STHSC device is reduced from 12.7% to 9.7%.