K. Gireesan

Bio: K. Gireesan is an academic researcher from Maharaja Sayajirao University of Baroda. The author has contributed to research in topics: Thin film & Band gap. The author has an hindex of 4, co-authored 5 publications receiving 48 citations.

Electrooptic properties of polycrystalline SnSe thin films

Abstract: It is observed from the studies of electrical resistivity of films of SnSe of different thicknesses and substrate temperatures that resistivity decreases with increase in thickness and substrate temperature. The study of variation in band gap with thickness shows a linear relationship between band gap and 1/t2. Finally, band gap – substrate temperature studies show that the band gap increases with substrate temperature.

Influence of heat treatment on the crystallization of thermally evaporated tin diselenide (SnSe2) thin films

Abstract: The thermal evaporation in vacuum of a stoichiometric bulk of SnSe 2 results in amorphous films and on annealing at 150°C for 3 h results in recrystallization of the film

Effect of heat treatment on the optical absorption of tin diselenide thin films

Abstract: Optical absorption measurements were made on tin diselenide thin films grown on glass substrates by thermal evaporation of stoichiometric bulk compound. In the as-deposited films, optical absorption was dominated by an indirect transition at lower photon energies with a band gap of 1.4 eV. The direct allowed transition with a band gap of 1.62 eV was predominant at higher energies. Annealing the film at elevated temperatures resulted in the decrease of both the direct and indirect transition band gaps.

Tin Selenide (SnSe): Growth, Properties, and Applications.

Abstract: The indirect bandgap semiconductor tin selenide (SnSe) has been a research hotspot in the thermoelectric fields since a ZT (figure of merit) value of 2.6 at 923 K in SnSe single crystals along the b-axis is reported. SnSe has also been extensively studied in the photovoltaic (PV) application for its extraordinary advantages including excellent optoelectronic properties, absence of toxicity, cheap raw materials, and relative abundance. Moreover, the thermoelectric and optoelectronic properties of SnSe can be regulated by the structural transformation and appropriate doping. Here, the studies in SnSe research, from its evolution to till now, are reviewed. The growth, characterization, and recent developments in SnSe research are discussed. The most popular growth techniques that have been used to prepare SnSe materials are discussed in detail with their recent progress. Important phenomena in the growth of SnSe as well as the problems remaining for future study are discussed. The applications of SnSe in the PV fields, Li-ion batteries, and other emerging fields are also discussed.

Perspectives on SnSe-based thin film solar cells: a comprehensive review

Abstract: Currently, selenium (Se)-based compound semiconductors (CISe, CIGSe and CZTSe) are considered as the active materials in the photovoltaic world. However, these materials exhibit couple of issues related to stoichiometry maintenance and scarcity of their constituent elements (In, Ga), which limit their massive production for future energy demands. These issues could be rectified by introducing a non-toxic, inexpensive and earth-abundant binary material. One such material is a tin monoselenide (SnSe), which exhibits a high chemical stability along with attractive physical properties namely, suitable band gap (1.3 eV), high absorption coefficient (105 cm−1) and p-type conductivity. These properties indicate SnSe as a competitive substitute in place of conventional absorbers in thin film solar cells. Despite of its remarkable properties, only a few reports were published on the fabrication of SnSe-based solar cells with poor efficiency (≤1 %). This indicates a need to review on the physical properties of SnSe and its device structures in a deeper sense. In this context, the present review describes the different methods of preparation of SnSe films and their physical properties along with the details of photovoltaic device fabrication. We highlighted the different factors that are limiting the efficiency of SnSe solar cells, and a few suggestions were included to overcome these problems for further improvement of these cells. This review will enrich and stimulate the readers to further investigate the growth of SnSe thin films and their devices, for the development of >20 % efficient SnSe solar cells.

Optical properties of tin diselenide films

Abstract: SnSe2 films were deposited on substrates at 300 K by a conventional thermal evaporation technique. The as-deposited films were amorphous and transformed to the crystalline phase on post-deposition annealing above 573 K in an inert atmosphere. The optical properties of the films were investigated, using spectrophotometric measurements of the transmittance and reflectance at normal incidence in the wavelength range 400–2000 nm. The refractive index data fit a single oscillator model with a dispersion parameter 5.149×10−14 and 5.773×10−14 eVm2 for the amorphous and crystalline films, respectively. The high-frequency dielectric constant of the amorphous films decreased from 9.871 to 7.475 for the crystalline films. The analysis of the spectral behaviour of the absorption coefficient in the intrinsic absorption region revealed an indirect forbidden and a direct allowed transition with energy gaps 0.99 and 2.05 eV for the amorphous films and 0.96 and 2.02 eV for the crystalline films, respectively.

Electrical and Photoelectrical Properties of Vacuum Deposited SnSe Thin Films

Abstract: Polycrystalline thin films of tin selenide have been prepared by vacuum deposition at a substrate temperature of 150°C and reported. X-ray diffraction, optical transmission, electrical conductivity and photoconductivity studies have been carried out on these films. Annealing the films at 300°C for 2 hours improves the crystallinity and a preferred orientation along the (111) plane develops. The optical transmission measurement reveals that the SnSe thin films have a direct allowed band gap of 1.26 eV. Electrical conductivity study shows that the conductivity increases with increasing temperature. The observed electrical conductivity at low temperature is explained based on hopping conduction mechanism. The photoconductivity measurement indicates the presence of continuously distributed deep localised gap states in this material.