Highlights
- Copper oxide thin films were spray-deposited at three substrate temperatures (523, 623, and 723 K) to find conditions favoring the CuO (tenorite) phase over Cu2O (cuprite).
- 623 K gave the best crystallinity; the other two substrate temperatures produced largely amorphous films.
- Raising the precursor concentration to 0.1 M at 623 K produced a purer tenorite (CuO) phase film.
- Post-deposition annealing up to 723 K increased crystallite size and crystallinity without shifting the crystal structure.
Abstract
This study examined how substrate and annealing temperatures affect spray-pyrolysis-deposited copper oxide thin films, targeting selective growth of the tenorite (CuO) phase over the alternative cuprite (Cu2O) phase. Films deposited at 523, 623, and 723 K substrate temperatures were compared, with 623 K giving the best crystallinity and a mix of both copper oxide phases; films at the other two temperatures were largely amorphous. Increasing the precursor concentration at the optimum 623 K substrate temperature yielded a purer tenorite (CuO) phase. Annealing these films at temperatures up to 723 K increased their crystallite size and crystallinity without shifting their crystal structure, while raising the copper concentration in the precursor sharply reduced the films' optical transmittance from about 80% to below 20%.
Research summary
Copper oxide is an inexpensive, non-toxic semiconducting material used in solar cells, gas sensors, and other devices, but it can form in two different phases — cuprite (Cu2O) or tenorite (CuO) — that have different electrical and optical properties. This study investigated how substrate temperature during spray pyrolysis, followed by post-deposition annealing, could be used to reliably favor the tenorite (CuO) phase.
What the study examined
- Copper oxide thin films spray-deposited on glass at three substrate temperatures (523, 623, and 723 K) using a cupric acetate precursor
- The effect of increasing precursor concentration (from 0.05 to 0.1 M) at the best-performing substrate temperature
- Structural changes from annealing the films afterward at 523, 623, and 723 K
- Optical transmittance, band gap, and electrical resistance across these deposition and annealing conditions
Main findings
Among the three substrate temperatures tested, 623 K produced the best-crystallized film, with a mix of cuprite and tenorite phases; films deposited at 523 K and 723 K were largely amorphous, likely because the precursor either did not fully decompose (too cool) or decomposed prematurely before reaching the substrate (too hot). Increasing the precursor concentration to 0.1 M at this optimum 623 K substrate temperature produced a purer tenorite (CuO) phase film.
Annealing these films afterward, up to 723 K, increased their crystallite size and crystallinity while leaving the underlying crystal structure and lattice parameters unchanged. Increasing the copper concentration in the precursor from 0.05 to 0.1 M also sharply reduced the film’s optical transmittance, from about 80% down to under 20% in the visible range, consistent with the more anisotropic tenorite phase becoming dominant.
Why it matters
By separately identifying the roles of substrate temperature, precursor concentration, and post-deposition annealing, the study provides a practical recipe for reliably producing the tenorite (CuO) phase of copper oxide by spray pyrolysis — a low-cost, scalable deposition method — rather than ending up with a mixed or amorphous film. That kind of phase control is a prerequisite for using copper oxide thin films confidently in solar cells, sensors, and other electronic devices.
Citation
S. Vignesh, Prabakaran Shankar, G. K. Mani, J. B. B. Rayappan. Growth and Characterization of Spray Pyrolysis Deposited Copper Oxide Thin Films: Influence of Substrate and Annealing Temperatures. Journal of Analytical and Applied Pyrolysis 111 (2015) 272-277.
