Nitrogen-Doped Cu2O Thin Films for Photovoltaic Applications

Ørnulf Nordseth,Irinela Chilibon,Edouard Monakhov,Kristin Bergum,Sean Erik Foss,Raj Kumar

doi:10.3390/ma12183038

Abstract

Cuprous oxide (Cu2O) is a p-type semiconductor with high optical absorption and a direct bandgap of about 2.1 eV, making it an attractive material for photovoltaic applications. For a high-performance photovoltaic device, the formation of low-resistivity contacts on Cu2O thin films is a prerequisite, which can be achieved by, for instance, nitrogen doping of Cu2O in order to increase the carrier concentration. In this work, nitrogen-doped p-type Cu2O thin films were prepared on quartz substrates by magnetron sputter deposition. By adding N2 gas during the deposition process, a nitrogen concentration of up to 2.3 × 1021 atoms/cm3 in the Cu2O thin films was achieved, as determined from secondary ion mass spectroscopy measurements. The effect of nitrogen doping on the structural, optical, and electrical properties of the Cu2O thin films was investigated. X-ray diffraction measurements suggest a preservation of the Cu2O phase for the nitrogen doped thin films, whereas spectrophotometric measurements show that the optical properties were not significantly altered by incorporation of nitrogen into the Cu2O matrix. A significant conductivity enhancement was achieved for the nitrogen-doped Cu2O thin films, based on Hall effect measurements, i.e., the hole concentration was increased from 4 × 1015 to 3 × 1019 cm−3 and the resistivity was reduced from 190 to 1.9 Ω⋅cm by adding nitrogen to the Cu2O thin films.

Highlights

Cuprous oxide (Cu2 O) 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 [1].To construct a p-n heterojunction, Cu2 O can be combined with various n-type metal oxide materials, such as for example ZnO, and one can foresee a heterojunction solar cell fully based on low-cost, abundant, and non-toxic metal oxides [2]
The data suggests that the nitrogen concentration in the N:Cu2 O thin films increases with increasing N2 gas flow during the deposition process
The film thickness decreases with increasing N2 gas flow rate, suggesting that the deposition rate for the N:Cu2 O thin film decreases with increasing N2 /Ar gas flow ratio during the sputter deposition process

Summary

Introduction

Cuprous oxide (Cu2 O) 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 [1].To construct a p-n heterojunction, Cu2 O can be combined with various n-type metal oxide materials, such as for example ZnO, and one can foresee a heterojunction solar cell fully based on low-cost, abundant, and non-toxic metal oxides [2]. A possible application of Cu2 O-based solar cells could be to combine them with conventional crystalline silicon (c-Si) solar cells in a mechanical stack of independently connected cells, enabling low-energy photons to be transmitted through the Cu2 O-based top subcell for subsequent absorption in the c-Si bottom subcell [5]. Such four-terminal tandem cell configuration has the potential to reach a power. A highly doped layer can, for instance, be obtained by tuning of the electrical properties of Cu2 O by adding foreign atoms, such as nitrogen which is an abundant and non-toxic element that can be straightforwardly incorporated into the Cu2 O lattice [10]

Objectives

Methods

Results

Conclusion