Indium sulphide (In2S3) is one of the best alternatives for CdS as a buffer layer in CuInGaSe2-based thin film heterojunction solar cells. In this work, In2S3 films were prepared by thermal evaporation of In2S3 powder onto glass substrates at different temperatures that vary from 200°C to 300°C. The as-grown films were characterized using appropriate techniques to evaluate the chemical and physical properties. The X-ray diffraction analysis revealed that all the films were polycrystalline in nature with a strong (109) plane as the preferred orientation and consisted of tetragonal and cubic phases. The crystallite size and the lattice parameters are calculated. The scanning electron micrographs indicated smooth surface with fine grains. The optical analysis revealed a high optical transmittance for the layers with a direct optical band gap that varied in the range of 1.8–2.2 eV.
Indium sulphide (In2S3) is a chalcogenide semiconductor that belongs to the III–VI group of semiconductors with interesting fundamental properties, useful for various device applications [
In recent years, In2S3 has proved to be an important alternative buffer layer to CdS in the fabrication of Cu(In,Ga) Se2-based solar cells with solar conversion efficiencies >15%. In2S3 layers have been synthesized using a variety of chemical as well as physical techniques. These include chemical vapour deposition [
In2S3 thin films were deposited by vacuum thermal evaporation using Hind Hi Vac Box Coater (model BC: 300). 4 N pure In2S3 powder, obtained from Sigma-Aldrich, was used as the source material and evaporated from molybdenum boat. The boat was covered with quartz wool to avoid spattering of the some material during evaporation. The deposition was carried out at a vacuum of 2 × 10−5 mbar on ultrasonically cleaned glass substrates. The distance between the source and substrate is kept as 7 cm. A 1KW radiant heater is used to heat the substrates. The substrate temperature (
The as-grown layers were characterized to study the properties using appropriate techniques. The morphological and chemical details were studied using Hitachi scanning electron microscope (SEM) connected with an Oxford energy dispersive X-ray analyzer (EDAX). The structural properties were evaluated using Seifert GE—X-ray Diffraction system—XRD 3003TT with a CuK
The visual observation indicated that all the grown layers appeared dark brown in color, homogeneous, and free from pin holes. The scratch tape test revealed that the layers were strongly adherent to the substrate surface. The films had a varying thickness of approximately 510–580 nm.
Figure
SEM pictures of In2S3 films grown at (a) 200°C, (b) 250°C and (c) 300°C.
The EDAX measurements on In2S3 layers revealed the presence of In and S peaks without any other impurity elements. The films formed at 200°C had shown higher S content that slowly decreased with the increase of substrate temperature. Figure
EDAX spectrum of In2S3 film grown at 300°C.
Figure
X-ray diffraction spectra of In2S3 films. T and C in the above figure refer to tetragonal and cubic crystal structures, respectively.
The lattice constants,
The optical transmittance spectra of In2S3 films grown at different substrate temperatures are shown in Figure
Transmittance verses wavelength spectra of In2S3 films.
Figure
Absorption coefficient versus photon energy plots.
In2S3 films were prepared on the glass substrates by thermal evaporation technique at different substrate temperatures. All the films were polycrystalline with the (109) plane as preferred orientation. Also, the layers showed a presence of both tetragonal and cubic phases where the later tend to minimize with the rise of substrate temperature. The evaluated crystallite size increased from 11.8 nm to 37.9 nm. All the layers showed a high optical transmittance, and the energy band gap increased with the rise of substrate temperature and varied in the range of 1.8–2.2 eV.
One of the authors, K. Ramya, thanks the University Grants Commission (UGC), New Delhi, for the financial assistance via the “UGC-BSR Research Fellowship.”