Surface treatment of electrodeposited n‐type Cu₂O thin films for applications in Cu₂O based devices

Abstract

In this Letter, we report the effects of ammonium sulfide [(NH4)2S] surface treatment on electrical and optical characteristics of the electrodeposited n‐type Cu2O thin films on Ti substrates. Films characterized structurally and morphologically before and after the surface treatment were compared using conductivity, spectral photoresponse and current–voltage (I–V) measurements. The ammonium sulfide surface treatment time showed an impact on optical and electrical characteristics of the films. Treated Cu2O films exhibited enhanced conductivity giving rise to a 50‐fold increase in the photocurrent and improved I–V characteristics. It was found that the sulfur passivation resulted in a nearly ohmic behaviour for Au or Ni contacts made with n‐type Cu2O whereas Ag or Cu contacts showed nearly Schottky behaviour. The results showed that ammonium sulfide treatments were very effective to passivate defects and improve the optical and electrical properties of polycrystalline n‐type Cu2O thin films that may provide a solid platform for Cu2O based devices of enhanced quality. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Annealing effects of the untreated and sulfur-treated electrodeposited n-type and p-type cuprous oxide thin films

“…Some of the key issues that need to be addressed in Cu 2 O thin film solar cell development is the associated high resistivity and defects of the Cu 2 O thin films. For device applications, especially, the minimization of surface defects such as those due to dangling bonds and nonradiative recombination centers in the Cu 2 O films is of utmost importance because it causes to reduce resistivity and enhance the electrical and optical properties . An obvious approach to modify surface and interface properties of semiconductors is to make the surface interact with foreign atoms, e.g., sulfur , selenium , chlorine , or simple radicals, e.g., cyanides .…”

“…Studies conducted by us on passivation of n‐Cu 2 O and p‐Cu 2 O thin films using ammonium sulfide have demonstrated that the film resistivity can be lowered while increasing the photoactivity of the related thin film solar cell structures. It was shown that the increase in the peak photocurrent was approximately a 50‐fold and 4‐fold, respectively, compared to the untreated n‐type Cu 2 O and p‐type Cu 2 O films . The passivation along with annealing was successfully used to improve the efficiency of Ti/p‐CuO/n‐Cu 2 O/Au solar cell.…”

“…Further studies with regard to structural and thermal stability of passivated and annealed Cu 2 O thin films will provide important information for improving the performance of such devices. Previously, it was verified that the sulfur passivation of both n‐Cu 2 O and p‐Cu 2 O thin films using ammonium sulfide led to the formation of Cu x S. However, the nature of the so formed Cu x S was not able to be examined by laboratory X‐ray diffraction which has limitations in providing complete information when the thin films consist of species in the form of very thin layers or dilute quantities. This can be circumvented by the use of high‐energy X‐ray diffraction (HEXRD) in which the diffraction data of high signal to noise ratio is capable of divulging structural information in a more accurate manner.…”

Defect engineering of the electronic transport through cuprous oxide interlayers

“…In particular, In 2 S 3 /Cu 2 O35 and ZnO/Cu 2 O36 interfaces have been found to be promising for photovoltaic applications. From the experimental point of view, the electrical resistivities of a Cu 2 O thin film between two gold leads using SiO 2 /Si substrates37, and of a sulfur-treated n-type Cu 2 O thin film with Ag, Cu, Au, or Ni front contacts have been measured38. However, very little is known about the theoretical understanding of electronic transport properties of heterojunctions involving Cu 2 O.…”

Preface: Focus on Functional Oxides

“…The 20 original Letters present exciting new research on the topics of transport properties [4], super-reducible oxides [5], ferroelectricity [6], point defects [7], memory applications [8][9][10], bulk properties [11][12][13][14], interfaces [15][16][17], surfaces [18][19][20] and catalytic properties [21][22][23].…”