Faculty Publications
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Item ZnSxSe1−x thin films: A study into its tunable energy band gap property using an experimental and theoretical approach(Elsevier Ltd, 2022) Ray, S.; Barman, B.; Darshan, C.; Tarafder, K.; Bangera, K.V.In recent times, ZnS and ZnSe thin films are drawing tremendous attention towards opto-electrical devices due to their optimal wide band gap energy. By alloying ZnS and ZnSe films to obtain ZnSxSe1−x thin films, the band gap of the ZnSxSe1−x film can be tuned to a value according to the device requirements. Herein, ZnSxSe1−x thin films were deposited on pre-cleaned glass substrates using a thermal evaporation system and the various properties of the obtained thin films were analyzed by altering the percentage of sulfur concentration in the films. The XRD analysis illustrated that the prepared films are polycrystalline in nature and oriented along cubic (1 1 1) plane. The deviation of (1 1 1) preferential peak position with composition ‘x’ along the absence of any secondary peaks confirms the formation of ternary ZnSxSe1−x thin films. DFT analysis verifies the formation of pristine ZnSxSe1−x alloy system. FESEM micrographs displayed that the ZnSxSe1−x thin films do not have any cracks or pinholes. EDAX analysis of the films revealed the existence of Zn, Se and S in an appropriate quantity. Optical analysis revealed the effective band gap tailoring of ZnSxSe1−x thin films. The band gap of the ZnSxSe1−x thin films increases from 2.59 eV to 3.38 eV as the composition ‘x’ varied from 0 to 1 and band composition was determined using the DOS plot obtained using VASP. © 2022 International Solar Energy SocietyItem Validation of ZnTe as back surface field layer for CdTe solar cells: A combined experimental and theoretical study(Elsevier Ltd, 2023) Ray, S.; Tarafder, K.An excellent back contact layer is one of the key requirements for thin-film solar cells with a high energy conversion efficiency. For a highly resistive compound such as CdTe thin-film, fabrication of contact with low electrical contact resistance along with a high electron affinity is very difficult. Herein, we have thoroughly investigated the possibility of using ZnTe as a back contact layer for CdTe-based solar cells through combined experimental and first-principle studies. CdTe and ZnTe thin films were deposited on the glass substrate. Detailed structural, morphological, elemental, electrical, and optical properties are investigated through different experimental techniques. Then p-ZnTe/n-CdTe heterojunction was fabricated, and junction properties were studied. Precise electronic band-structures were obtained for CdTe, ZnTe, and CeTe/ZnTe heterojunctions. The interface properties, band edge position, and band alignments were estimated by using the HSE06 hybrid functional method. Detailed theoretical results substantiate our experimental findings. © 2023 Elsevier B.V.Item Temperature-dependent in situ Cd substitution at Zn sites in Cu2ZnSnS4 thin films via sol–gel method: Experimental and DFT insights(Elsevier B.V., 2025) Chennangod, S.; Ray, S.; P, A.S.; Tarafder, K.; Bhat, T.N.We report a systematic study of in situ cadmium (Cd) substitution at Zinc (Zn) sites in Cu2ZnSnS4 (CZTS) thin films synthesized via a scalable sol–gel route, with sulfurization carried out at 300 °C, 400 °C, and 500 °C. X-ray diffraction and Raman spectroscopy demonstrate that higher sulfurization temperatures along with increased Cd content progressively suppress the secondary Cu2SnS3 phase, while field-emission SEM and atomic force microscopy reveal enhanced grain growth and a smoother granular surface. UV–Vis absorption measurements show a continuous band-gap reduction from 1.43 eV in undoped CZTS to 1.20 eV at the highest Cd level, corroborated by a red shift in photoluminescence emission. X-ray photoelectron spectroscopy and density functional theory (GGA-PBE and HSE06) with orbital-projected density of states (p-DOS) analyses attribute this narrowing to localized Cd-induced states near the conduction band minimum and lattice expansion effects. Additionally, preliminary photovoltaic characterization demonstrated improved device performance for the Cd:CZTS solar cell compared to the pristine CZTS cell, exhibiting higher photocurrent density and enhanced external quantum efficiency. These results confirm that precise control of sulfurization temperature and Cd incorporation not only tailors the electronic structure and band gap but also suppresses undesirable secondary phases, offering a promising route to optimize kesterite thin films for high-efficiency photovoltaic applications. © 2025 Elsevier B.V.