Teny Theresa John

Characterization of spray pyrolysed indium sulfide thin films

Indium sulfide thin films have been prepared using the chemical spray pyrolysis technique. Samples with different substrate temperatures and indium-to-sulfur (In/S) ratios have been prepared and characterized using x-ray diffraction (XRD), x-ray photoelectron spectroscopy, photosensitivity measurements and optical absorption studies. XRD studies have revealed that the samples are β-In2S3. The optical bandgap has been found to decrease from 2.81 to 2.64 eV with the In/S ratio varying from 2/1 to 2/8. The photoresponse of the samples can be improved by changing either the In/S ratio in the solution or the substrate temperature. From this study we observe that, in terms of crystallinity, bandgap and photoresponse, the sample with the In/S ratio of 1.2/8 is very suitable for any photovoltaic application.

Defect analysis of sprayed β-In2S3 thin films using photoluminescence studies

In this paper we report for the first time the results of photoluminescence (PL) studies on thin films of a β-In2S3 compound semiconductor, grown using a chemical spray pyrolysis (CSP) technique. PL emission in the wavelength range 550–900 nm was recorded using a 488 nm line from a Ar+ laser as the excitation source. There were two PL bands, centred at 568 nm (band A) and 663 nm (band B). A shift in the PL peak energy and full width at half maximum of the former band due to a variation in temperature strongly suggested that the emission followed the Cartesian coordinate (CC) model of luminescence, while the latter was found to have arisen from transitions between a donor–acceptor pair. Band A was most dominant in the sulfur-deficient sample and hence associated with a sulfur vacancy, while band B was dominant in the indium-rich sample and hence linked with indium interstitials. The proposed energy level scheme allowed us to interpret the recombination processes in β-In2S3 thin films.

Photoconductivity in sprayed β-In2S3 thin films under sub-band-gap excitation of 1.96 eV

β-In2S3 thin films with a band gap of ∼2.67eV exhibited persistent photoconductivity when excited using photons with energy of 1.96 eV. The photoconductive response to extrinsic photoexcitation could be removed when the film stoichiometry was changed. Photoluminescence studies in the films revealed an emission of 1.826 eV, due to donor–acceptor pair (DAP) recombination, which was absent in the film not responding to extrinsic excitation. Hence, it was concluded that presence of the DAP was responsible for the extrinsic photoconductivity under the 1.96 eV excitation. This study can initiate further a methodology for tailoring the photoresponse of this semiconducting thin film by spatially controlling the film stoichiometry.

Do the grain boundaries of β-In2S3 thin films have a role in sub-band-gap photosensitivity to 632.8nm?

Highly photoconducting β-In2S3 thin films with conducting grain boundaries were obtained, using “chemical spray pyrolysis” technique. By varying the atomic ratio of the precursor solution used for spray pyrolysis, the photoconductivity of these films could be tailored. Conducting grain boundaries were found only for samples with a specific stoichiometry and these films exhibited photoresponse to intrinsic and extrinsic excitation wavelengths in the range of 325–532nm. Postdeposition vacuum annealing of these films enhanced the grain boundary conductivity, caused the films to exhibit persistent photoconductivity for both intrinsic and extrinsic excitations and extended the extrinsic photoresponse to wavelengths beyond 632.8nm. Photoresponse to excitation wavelength of 632.8nm was observed in films with and without conducting grain boundaries which proved that the extrinsic photoresponse to this wavelength was an effect associated with the defect chemistry of the β-In2S3.

Implantation assisted copper diffusion: A different approach for the preparation of CuInS2∕In2S3 p-n junction

Copper indium sulfide thin films were prepared using copper diffusion into argon ion implanted In2S3 thin films. A comparative study of copper diffusion in pristine and ion implanted In2S3 samples was also performed. It was found that copper indium sulfide formation was much better in argon implanted samples compared to that in unimplanted samples. Copper diffusion in implanted samples enabled us to prepare an In2S3∕CuInS2 solar cell. The fill factor of the cell prepared was 30.2% and the efficiency was 0.34%.

Structural and Optical Properties of Indium Sulfide Thin Films Prepared by Silar Technique

Indium sulfide thin films were prepared using a relatively new, simple and inexpensive technique called Suc- cessive Ionic Layer Adsorption and Reaction (SILAR). SILAR deposition conditions for obtaining good quality � -Indium sulfide (In2S3) films were optimized. The films were structurally and optically characterized using X-ray diffraction (XRD), photosensitivity measurements and optical absorption studies. Effects of using different precursor solutions, in- dium chloride (InCl3) and indium nitrate (In(NO3)3) and post deposition annealing were also studied. Films fabricated with In(NO3)3 showed good crystallinity without any post deposition annealing while films prepared using InCl3 were crystalline only when annealed at 400 0 C. The band gap of the films varied from 2.32 to 2.92 eV depending on the deposi- tion conditions.