Review on Cu2SnS3, Cu3SnS4, and Cu4SnS4 thin films and their photovoltaic performance

Vasudeva Reddy Minnam Reddy,Mohan Reddy Pallavolu,Phaneendra Reddy Guddeti,Sreedevi Gedi,Kishore Kumar Yarragudi Bathal Reddy,Babu Pejjai,김우경,Thulasi Ramakrishna Reddy Kotte,박진호 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.76 No.-

The rapid progress on the Cu–Sn–S (Cu2SnS3, Cu3SnS4, and Cu4SnS4) solar cells has opened a new avenueto generate the electrical energy at ultra-low-cost. Therefore, the progress in the deposition of Cu2SnS3,Cu3SnS4, and Cu4SnS4 thinfilms by various chemical and physical methods is reviewed comprehensively. This article briefly describes (i) the phase diagrams of Cu–Sn–S, (ii) the bulk properties of Cu2SnS3,Cu3SnS4, and Cu4SnS4, (iii) the effect of deposition conditions on the phase formation, (iv) the physicalproperties of Cu2SnS3, Cu3SnS4, and Cu4SnS4 thinfilms, and (v) the photovoltaic performance of Cu2SnS3,Cu3SnS4, and Cu4SnS4 solar cells.

Hypermethylation of Promoter Region of LATS1 - a CDK Interacting Protein in Oral Squamous Cell Carcinomas - a Pilot Study in India

Reddy, Vijaya Ramakrishna,Annamalai, Thangavelu,Narayanan, Vivek,Ramanathan, Arvind Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.4

Background: Epigenetic silencing of tumor suppressor genes due to promoter hypermethylation is one of the frequent mechanisms observed in cancers. Hypermethylation of several tumor suppressor genes involved in cell cycle regulation has been reported in many types of tumors including oral squamous cell carcinomas. LATS1 (Large Tumor Suppressor, isoform 1) is a novel tumor suppressor gene that regulates cell cycle progression by forming complexes with the cyclin dependent kinase, CDK1. Promoter hypermethylation of the LATS1 gene has been observed in several carcinomas and also has been linked with prognosis. However, the methylation status of LATS1 in oral squamous cell carcinomas is not known. As oral cancer is one of the most prevalent forms of cancer in India, the present study was designed to investigate the methylation status of LATS1 promoter and associate it with histopathological findings in order to determine any associations of the genetic status with stage of differentiation. Materials and Methods: Tumor chromosomal DNA isolated from biopsy tissues of thirteen oral squamous cell carcinoma biopsy tissues were subjected to digestion with methylation sensitive HpaII enzyme followed by amplification with primers flanking CCGG motifs in promoter region of LATS1 gene. The PCR amplicons were subsequently subjected to agarose gel electrophoresis along with undigested amplification control. Results: HpaII enzyme based methylation sensitive PCR identified LATS1 promoter hypermethylation in seven out of thirteen oral squamous cell carcinoma samples. Conclusions: The identification of LATS1 promoter hypermethylation in seven oral squamous cell carcinoma samples (54%), which included one sample with epithelial dysplasia, two early invasive and one moderately differentiated lesions indicates that the hypermethylation of this gene may be one of the early event during carcinogenesis. To the best of our knowledge, this is the first study to have explored and identified positive association between LATS1 promoter hypermethylation with histopathological features in oral squamous cell carcinomas.

EFFECT OF SULFURIZATION TIME ON THE EFFICIENCY OF SnS-BASED SOLAR CELLS

Vasudeva Reddy MINNAM REDDY,Sreedevi GEDI,Babu PEJJAI,Ramakrishna Reddy KT,Chinho PARK 한국신재생에너지학회 2015 AFORE Vol.2015 No.11

Effect of sulfurization temperature on the efficiency of SnS solar cells fabricated by sulfurization of sputtered tin precursor layers using effusion cell evaporation

Minnam Reddy, Vasudeva Reddy,Cho, Haeyun,Gedi, Sreedevi,Reddy, K.T. Ramakrishna,Kim, Woo Kyoung,Park, Chinho Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.806 No.-

<P><B>Abstract</B></P> <P>Earth-abundant tin monosulfide (SnS) thin films have attracted considerable interest for eco-friendly and low-cost thin film solar cells. However, less attention has been paid on the fabrication of SnS solar cell by the industrial processes. In view of that the current study aimed to fabricate the SnS solar cells via two-stage (sputtering + sulfurization) industrial process. For the preparation of SnS thin films, first tin metallic precursor layers were deposited by DC sputtering and then sulfurized using the rapid thermal effusion cell evaporation process. The effect of sulfurization temperature on the physical properties of SnS thin films and the efficiency of SnS solar cells was examined. Formation of the single phase SnS thin films was confirmed when the tin metallic precursor layers sulfurized in the range of 450–470 °C, whereas secondary phases of Sn, SnS<SUB>2</SUB>, and Sn<SUB>2</SUB>S<SUB>3</SUB> were noticed at the sulfurization temperature lower than 450 °C and re-evaporation of deposited SnS thin films was observed at the sulfurization temperature higher than 470 °C. Solar cell fabricated with SnS absorber sulfurized at a temperature of 470 °C showed the conversion efficiency of ∼ 2.3%. The causes for lower efficiency of these solar cells were recombination in the SnS absorber and non-uniform compositional distribution of Cd, S and Sn as a function of depth in the CdS/SnS/Mo structure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> SnS films were grown via sulfurization using effusion cell evaporation method. </LI> <LI> Effect of sulfurization temperature on the efficiency of SnS solar cells was examined. </LI> <LI> A high efficiency of ∼2.3% for SnS solar cells was achieved at 470 °C. </LI> <LI> The causes for lower efficiency of these solar cells were investigated. </LI> </UL> </P>

Microwave sintering of nickel ferrite nanoparticles processed via sol–gel method

Penchal Reddy, M.,Madhuri, W.,Sadhana, K.,Kim, I. G.,Hui, K. N.,Hui, K. S.,Siva Kumar, K. V.,Ramakrishna Reddy, R. Springer-Verlag 2014 Journal of sol-gel science and technology Vol.70 No.3

Development of sulphurized SnS thin film solar cells

MINNAM REDDY VASUDEVA REDDY,Sreedevi Gedi,박진호,Miles R.W,Ramakrishna Reddy K.T 한국물리학회 2015 Current Applied Physics Vol.15 No.5

Thin films of tin sulphide (SnS) have been grown by sulphurization of sputtered tin precursor layers in a closed chamber. The effect of sulphurization temperature (Ts) that varied in the range of 150-450 ℃ for a fixed sulphurization time of 120 min on SnS film was studied through various characterization techniques. X-ray photoelectron spectroscopy analysis demonstrated the transformation of metallic tin layers into SnS single phase for Ts between 300 ℃ and 350 ℃. The X-ray diffraction measurements indicated that all the grown films had the (111) crystal plane as the preferred orientation and exhibited orthorhombic crystal structure. Raman analysis showed modes at 95 cm-1, 189 cm-1 and 218 cm-1 are related to the Ag mode of SnS. AFM images revealed a granular change in the grain growth with the increase of Ts. The optical energy band gap values were estimated using the transmittance spectra and found to be varied from 1.2 eV to 1.6 eV with Ts. The Hall effect measurements showed that all the films were p-type conducting nature and the layers grown at 350 ℃ showed a low electrical resistivity of 64 Ω-cm, a net carrier concentration of 2 × 1016 cm3 and mobility of 41 cm2 V-1 s-1. With the use of sprayed Zn0.76Mg0.24O as a buffer layer and the sputtered ZnO:Al as window layer, the SnS based thin film solar cell was developed that showed a conversion efficiency of 2.02%.

Determination of the Minority Carrier Diffusion Length of SnS Using Electro-Optical Measurements

K. T. Ramakrishna Reddy,P. A. Nwofe,R. W. Miles 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.3

The minority carrier diffusion length of the “absorber layer” in a solar cell is generally accepted to be one of the most important parameters that govern the performance of a solar cell device. In this work, thin films of SnS have been thermally evaporated onto cadmium sulphide/indium tin oxide/glass substrates, to fabricate heterojunction solar cell devices. The minority carrier diffusion length was determined for the first time for SnS layers using spectral response measurements in conjunction with optical absorption coefficient versus wavelength measurements. The minority carrier diffusion length was determined to be in the range 0.18 -0.23 μm for the SnS/CdS devices investigated in this work.

Microwave sintering of iron deficient Ni–Cu–Zn ferrites for multilayer chip inductors

M. Penchal Reddy,W. Madhuri,G. Balakrishnaiah,N. Ramamanohar Reddy,K.V. Sivakumar,V.R.K. Murthy,R. Ramakrishna Reddy 한국물리학회 2011 Current Applied Physics Vol.11 No.2

This study was aimed at the low temperature synthesis of iron deficient samples of Ni―Cu―Zn ferrite using the microwave sintering technique. The samples were sintered at 950 ℃ for 30 min. Microstuctural and structural analyses were carried out using a scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The lattice parameter was found to increase with increasing nickel concentration. The porosity calculated using X-ray density and measured density also shows a decreasing behavior with increasing nickel concentration. The variation of saturation magnetization was studied as a function of nickel concentration. All the compositions indicate that they are ferrimagnetic in nature. Initial permeability plotted against temperature at 10 kHz showed a sharp drop at Curie transition temperature and values observed at transition are found to be dependent on the nickel concentration. The dielectric constant, dielectric loss tangent and ac conductivity of all samples were measured at room temperature as a function of frequency. These parameters decrease with increase in frequency for all of the samples. The present ferrites are well suitable for the application in multilayer chip inductor due to its low temperature sinterability, good magnetic properties and low loss at high frequency.

Photoluminescence Study of Chemical Bath Deposited ZnIn2Se4 Thin Films

Pejjai Babu,MINNAM REDDY VASUDEVA REDDY,Kotte Tulasi Ramakrishna Reddy 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.4

Thin films of ZnIn2Se4 (ZIS) have been prepared by chemical bath deposition (CBD) using a novel and water soluble Na2SeO3 as a source of selenium ion for the first time. The deposition of the films was carried out at various pH values in the range of 6 - 11, keeping all other bath parameters at optimised values. EDAX analysis revealed that all the grown layers were selenium deficient with trace amounts of oxygen and chlorine incorporation. FTIR spectral measurements revealed the associated symmetric and asymmetric stretching modes of bridged oxygen atoms on the surface of the films. The room temperature photoluminescence properties of these samples at different pH values are studied in detail. Further, Gaussian curve fitting was employed to deconvolute the PL spectra and the change in intensities of these peaks with respective to pH values was addressed and correlated to the role of native defects that were incorporated while deposition. The results indicate that the variation of solution pH had a noticeable effect on the photoluminescence ZIS films.

Influence of substrate temperature on physical properties of sprayed Zn0.85Mn0.15O films

L. Raja Mohan Reddy,P. Prathap,K.T. Ramakrishna Reddy 한국물리학회 2009 Current Applied Physics Vol.9 No.3

Zn1-xMnxO thin films have been synthesized by chemical spray pyrolysis at different substrate temperatures in the range, 250–450 ℃ for a manganese composition, x = 15%, on corning 7059 glass substrates. The as-grown layers were characterized to evaluate their chemical and physical behaviour with substrate temperature. The change of dopant level in ZnO films with substrate temperature was analysed using X-ray photoelectron spectroscope measurements. The X-ray diffraction studies revealed that all the films were strongly oriented along the (002) orientation that correspond to the hexagonal wurtzite structure. The crystalline quality of the layers increased with the increase of substrate temperature up to 400 ℃ and decreased thereafter. The crystallite size of the films varied in the range, 14–24 nm. The surface morphological studies were carried out using atomic force microscope and the layers showed a lower surface roughness of 4.1 nm. The optical band gap of the films was ~3.35 eV and the electrical resistivity was found to be high, ~104Ωcm. The films deposited at higher temperatures (>350 ℃) showed ferromagnetic behaviour at 10 K. Zn1-xMnxO thin films have been synthesized by chemical spray pyrolysis at different substrate temperatures in the range, 250–450 ℃ for a manganese composition, x = 15%, on corning 7059 glass substrates. The as-grown layers were characterized to evaluate their chemical and physical behaviour with substrate temperature. The change of dopant level in ZnO films with substrate temperature was analysed using X-ray photoelectron spectroscope measurements. The X-ray diffraction studies revealed that all the films were strongly oriented along the (002) orientation that correspond to the hexagonal wurtzite structure. The crystalline quality of the layers increased with the increase of substrate temperature up to 400 ℃ and decreased thereafter. The crystallite size of the films varied in the range, 14–24 nm. The surface morphological studies were carried out using atomic force microscope and the layers showed a lower surface roughness of 4.1 nm. The optical band gap of the films was ~3.35 eV and the electrical resistivity was found to be high, ~104Ωcm. The films deposited at higher temperatures (>350 ℃) showed ferromagnetic behaviour at 10 K.