Metal Oxide Thin-Film Heterojunctions for Photovoltaic Applications.

Ørnulf Nordseth,Sean Foss,Raj Kumar,Bengt Svensson,Laurentiu Fara,Kristin Bergum,Florin Dragan,Constantin Dumitru,Dan Craciunescu,Irinela Chilibon,Edouard Monakhov

doi:10.3390/ma11122593

Abstract

Silicon-based tandem solar cells incorporating low-cost, abundant, and non-toxic metal oxide materials can increase the conversion efficiency of silicon solar cells beyond their conventional limitations with obvious economic and environmental benefits. In this work, the electrical characteristics of a metal oxide thin-film heterojunction solar cell based on a cuprous oxide (Cu2O) absorber layer were investigated. Highly Al-doped n-type ZnO (AZO) and undoped p-type Cu2O thin films were prepared on quartz substrates by magnetron sputter deposition. The electrical and optical properties of these thin films were determined from Hall effect measurements and spectroscopic ellipsometry. After annealing the Cu2O film at 900 °C, the majority carrier (hole) mobility and the resistivity were measured at 50 cm2/V·s and 200 Ω·cm, respectively. Numerical modeling was carried out to investigate the effect of band alignment and interface defects on the electrical characteristics of the AZO/Cu2O heterojunction. The analysis suggests that the incorporation of a buffer layer can enhance the performance of the heterojunction solar cell as a result of reduced conduction band offset.

Highlights

The photovoltaic (PV) market is currently dominated by wafer-based crystalline silicon solar cells, with a market share of more than 90% [1]
Figure deposited on quartz; (b) Tauc plot for the as-grown and annealed cuprous oxide (Cu2 O) and Al-doped n-type ZnO (AZO) thin films deposited on quartz
The results suggest that the electrical performance of the AZO/Cu2 O heterojunction solar cell is reduced with increasing ND, Cu2O, e.g., for the Cu2 O absorber layer (tCu2O) = 2 μm the conversion efficiency decreases from 10.4% for ND, Cu2O = 1 × 1014 cm−3 to

Summary

Introduction

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 (Cu2 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]. For ZnO/Cu2 O heterojunction solar cells, the properties of the heterojunction interface are critical in order to obtain high power conversion efficiency. Reducing the defect density at the heterojunction interface to a minimum is important in order to avoid recombination losses

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