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)

Grain size of polycrystalline semiconductor thin films in solar cells is optimized to enhance the efficiency of solar cells. This paper reports results on an investigation carried out on electrodeposited n-type cuprous oxide (Cu 2 O) thin films on Ti substrates with small crystallites and sulfidation of them to produce a thin-film solar cell. During electrodeposition of Cu 2 O films, pH of an aqueous acetate bath was optimized to obtain films of grain size of about 100 nm, that were then used as templates to grow thicker n-type nanocrystalline Cu 2 O films. XRD and SEM analysis revealed that the films were of single phase and the substrates were well covered by the films. A junction of Cu 2 O/Cu x S was formed by partially sulfiding the Cu 2 O films using an aqueous sodium sulfide solution. It was observed that the photovoltaic properties of nano Cu 2 O/Cu x S heterojunction structures are better than micro Cu 2 O/Cu x S heterojunction solar cells. Resulting Ti/nano Cu 2 O/Cu x S/Au solar cell structure produced an energy conversion efficiency of 0.54%, V oc = 610 mV and J sc = 3.4 mA cm −2 , under AM 1.5 illumination. This is a significant improvement compared to the use of microcrystalline thin film Cu 2 O in the solar cell structure where the efficiency of the cell was limited to 0.11%. This improvement is attributed mainly to the increased film surface area associated with nanocrystalline Cu 2 O films.

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