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

Abstract

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/Cu 2 O subcell on top of a silicon-based subcell were studied by optical modelling. Cu 2 O 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 Cu 2 O thin films were prepared on quartz substrates by magnetron sputter deposition. Thermal annealing of the Cu 2 O 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 cm 2 /V⋅s and the resistivity decreases from 560 to 200 Ω⋅cm after annealing. A Cu 2 O absorber layer of 2 µm thickness will generate about 10 mA/cm 2 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/Cu 2 O 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/Cu 2 O subcell are obtained for a thickness of approximately 80 nm for both the top How to cite this paper: Nordseth, Ø.,

Metal Oxide Thin-Film Heterojunctions for Photovoltaic Applications

“…The photovoltaic (PV) market is currently dominated by wafer-based crystalline silicon solar cells, with a market share of more than 90% [1]. Further cost reductions for this technology can be achieved by developing silicon-based tandem solar cells employing low-cost, abundant, and non-toxic metal oxide materials [2]. Among these metal oxides is cuprous oxide (Cu 2 O), which is considered an attractive material for photovoltaic applications since it is a p-type semiconductor with high optical absorption and a direct bandgap of about 2.1 eV, yielding a theoretical power conversion efficiency limit close to 20% under 1 sun illumination [3].…”

Complex Investigation of High Efficiency and Reliable Heterojunction Solar Cell Based on an Improved Cu2O Absorber Layer

“…The present study is based on numerical electro-optical modeling and reliability analysis and is dedicated to increasing the performance and reliability of heterojunction solar cells [8][9][10]; it is correlated with the experimental investigation (morphological, structural, and optical) of an improved Cu 2 O absorber layer. Its morphological and structural characterization is based on SEM, AFM, and XRD analyses [11].…”

Semi-Transparent p-Cu2O/n-ZnO Nanoscale-Film Heterojunctions for Photodetection and Photovoltaic Applications

“…Moreover, its large absorption coefficient makes it suitable for photovoltaic applications: as p-type absorber layer in combination with n-type wide bandgap semiconductor oxides such as ZnO, TiO2, and Ga2O3 [10][11][12] , as hole transport layer in perovskite solar cells, 13 and as top cell of Si-based tandem solar cells in combination with ZnO. 14 With its relatively large bandgap Cu2O is considered as suitable for thin film transparent and semi-transparent photovoltaics applications in combination with ZnO. 15 Cu2O/ZnO heterojunctions have been also investigated for visible and UV photodetection.…”