M. T. S. Nair

Bio: M. T. S. Nair is an academic researcher from National Autonomous University of Mexico. The author has contributed to research in topics: Thin film & Chemical bath deposition. The author has an hindex of 40, co-authored 116 publications receiving 4359 citations.

Chemically Deposited Sb2 S 3 and Sb2 S 3 ‐ CuS Thin Films

Abstract: Thin films of antimony sulfide have been deposited from chemical baths containing antimony trichloride and sodium thiosulfate maintained at 10 C. Upon annealing in nitrogen at 300 C for 1 h, the films become photosensitive with photo- to dark-current ratio of two to three orders of magnitude at 2 kW/m{sup 2} tungsten halogen radiation. The annealed films are crystalline with an X-ray diffraction pattern matching that of stibnite, Sb{sub 2}S{sub 3}, (JCPDS 6-0474) and show an optical bandgap of 1.78 eV. Deposition of a thin film of CuS on the antimony sulfide thin film and subsequent annealing in nitrogen at 250 C for 1 h produces films with acceptable solar control characteristics: integrated visible transmittance, T{sub vis}, 15%; integrated visible reflectance, R{sub vis}, 12%; integrated infrared transmittance, T{sub ir}, 14%; integrated infrared reflectance, R{sub ir}, 36%; and a shading coefficient of about 0.35. The X-ray diffraction patterns of the annealed Sb{sub 2}S{sub 3}-CuS thin films indicate the formation of a ternary compound with the structure of famatinite, Cu{sub 3}SbS{sub 4}.

Cu2SnS3 and Cu4SnS4 Thin Films via Chemical Deposition for Photovoltaic Application

Abstract: Thin films of copper sulfide (CuS, 200 nm thick) were deposited over thin films of tin sulfide (SnS, 180 nm thick) by sequential chemical deposition. The layers were heated in nitrogen atmosphere at 350 and 400°C. The grazing incidence X-ray diffraction analysis of these layers established the formation of thin films of ternary composition, Cu 2 SnS 3 and Cu 4 SnS 4 . Optical bandgaps of the films are direct, 0.95 eV for Cu 2 SnS 3 and 1.2 eV for Cu 4 SnS 4 , and the electronic transitions are of the forbidden type in both cases. The films are p-type, with electrical conductivities of 0.5-10 Ω ―1 cm ―1 and hole concentrations of 10 17 ―10 18 cm ―3 . Based on the optical absorption coefficients, the light generated current density (J L ) as a solar cell absorber was evaluated for these materials for air mass 1.5 (1000 W/m 2 ) global solar radiation. For a film thickness of 0.5 μm. Cu 2 SnS 3 and Cu 4 SnS 4 could offer J L of 34 and 27 mA/cm 2 , respectively. Corresponding optical conversion efficiencies of solar energy into electron-hole pairs are 32 and 24%. The built-in potential for CdS/Cu 2 SnS 3 and CdS/Cu 4 SnS 4 junctions would be above 0.9 V and above 1.1 V when ZnO replaces CdS as the window layer.

Copper selenide thin films by chemical bath deposition

Abstract: We report the structural, optical, and electrical properties of thin films (0.05 to 0.25 μm) of copper selenide obtained from chemical baths using sodium selenosulfate or N,N-dimethylselenourea as a source of selenide ions. X-ray diffraction (XRD) studies on the films obtained from baths using sodium selenosulfate suggest a cubic structure as in berzelianite, Cu 2− x Se with x =0.15. Annealing the films at 400°C in nitrogen leads to a partial conversion of the film to Cu 2 Se. In the case of films obtained from the baths containing dimethylselenourea, the XRD patterns match that of klockmannite, CuSe. Annealing these films in nitrogen at 400°C results in loss of selenium, and consequently a composition rich in copper, similar to Cu 2− x Se, is reached. Optical absorption in the films result from free carrier absorption in the near infrared region with absorption coefficient of ∼10 5 cm −1 . Band-to-band transitions which gives rise to the optical absorption in the visible-ultraviolet region may be interpreted in terms of direct allowed transitions with band gap in the 2.1–2.3 eV range and indirect allowed transitions with band gap 1.2–1.4 eV. All the films, as prepared and annealed, show p-type conductivity, in the range of (1–5)×10 3 Ω −1 cm −1 . This results in high near infrared reflectance, of 30–80%.

Structural and chemical transformations in SnS thin films used in chemically deposited photovoltaic cells

Abstract: Chemically deposited SnS thin films possess p-type electrical conductivity. We report a photovoltaic structure: SnO 2 :F–CdS–SnS–(CuS)–silver print, with V oc > 300 mV and J sc up to 5 mA/cm 2 under 850 W/m 2 tungsten halogen illumination. Here, SnO 2 :F is a commercial spray-CVD (Pilkington TEC-8) coating, and the rest deposited from different chemical baths: CdS (80 nm) at 333 K, SnS (450 nm) and CuS (80 nm) at 293–303 K. The structure may be heated in nitrogen at 573 K, before applying the silver print. The photovoltaic behavior of the structure varies with heating: V oc ≈ 400 mV and J sc 2 , when heated at 423 K in air, but V oc decreases and J sc increases when heated at higher temperatures. These photovoltaic structures have been found to be stable over a period extending over one year by now. The overall cost of materials, simplicity of the deposition process, and possibility of easily varying the parameters to improve the cell characteristics inspire further work. Here we report two different baths for the deposition of SnS thin films of about 500 nm by chemical deposition. There is a considerable difference in the nature of growth, crystalline structure and chemical stability of these films under air-heating at 623–823 K or while heating SnS–CuS layers, evidenced in XRF and grazing incidence angle XRD studies. Heating of SnS–CuS films results in the formation of SnS–Cu x SnS y . ‘All-chemically deposited photovoltaic structures’ involving these materials are presented.

Antimony sulfide thin films in chemically deposited thin film photovoltaic cells

Abstract: Antimony sulfide thin films of thickness ≈ 500 nm have been deposited on glass slides from chemical baths constituted with SbCl3 and sodium thiosulfate. Smooth specularly reflective thin films are obtained at deposition temperatures from − 3 to 10 °C. The differences in the film thickness and improvement in the crystallinity and photoconductivity upon annealing the film in nitrogen are presented. These films can be partially converted into a solid solution of the type Sb2SxSe3 − x, detected in X-ray diffraction, through heating them in contact with a chemically deposited selenium thin film. This would decrease the optical band gap of the film from ≈ 1.7 eV (Sb2S3) to ≈ 1.3 eV for the films heated at 300 °C. Similarly, heating at 300 °C of sequentially deposited thin film layers of Sb2S3–Ag2Se, the latter also from a chemical bath at 10 °C results in the formation of AgSb(S/Se)2 with an optical gap of ≈ 1.2 eV. All these thin films have been integrated into photovoltaic structures using a CdS window layer deposited on 3 mm glass sheets with a SnO2:F coating (TEC-15, Pilkington). Characteristics obtained in these cells under an illumination of 850 W/m2 (tungsten halogen) are as follows: SnO2:F–CdS–Sb2S3–Ag(paint) with open circuit voltage (Voc) 470 mV and short circuit current density (Jsc) 0.02 mA/cm2; SnO2:F–CdS–Sb2S3–CuS–Ag(paint), Voc ≈ 460 mV and Jsc ≈ 0.4 mA/cm2; SnO2:F–CdS–Sb2SxSe3 − x–Ag(paint), Voc ≈ 670 mV and Jsc ≈ 0.05 mA/cm2; SnO2:F–CdS–Sb2S3–AgSb(S/Se)2–Ag(paint), Voc ≈ 450 mV and Jsc ≈ 1.4 mA/cm2. We consider that the materials and the deposition techniques reported here are promising toward developing ‘all-chemically deposited solar cell technologies.’

A Layered Hybrid Perovskite Solar-Cell Absorber with Enhanced Moisture Stability

Abstract: Two-dimensional hybrid perovskites are used as absorbers in solar cells. Our first-generation devices containing (PEA)2(MA)2[Pb3I10] (1; PEA=C6H5(CH2)2NH3+, MA=CH3NH3+) show an open-circuit voltage of 1.18 V and a power conversion efficiency of 4.73 %. The layered structure allows for high-quality films to be deposited through spin coating and high-temperature annealing is not required for device fabrication. The 3D perovskite (MA)[PbI3] (2) has recently been identified as a promising absorber for solar cells. However, its instability to moisture requires anhydrous processing and operating conditions. Films of 1 are more moisture resistant than films of 2 and devices containing 1 can be fabricated under ambient humidity levels. The larger bandgap of the 2D structure is also suitable as the higher bandgap absorber in a dual-absorber tandem device. Compared to 2, the layered perovskite structure may offer greater tunability at the molecular level for material optimization.

A review of solar photovoltaic technologies

Abstract: Global environmental concerns and the escalating demand for energy, coupled with steady progress in renewable energy technologies, are opening up new opportunities for utilization of renewable energy resources. Solar energy is the most abundant, inexhaustible and clean of all the renewable energy resources till date. The power from sun intercepted by the earth is about 1.8 × 1011 MW, which is many times larger than the present rate of all the energy consumption. Photovoltaic technology is one of the finest ways to harness the solar power. This paper reviews the photovoltaic technology, its power generating capability, the different existing light absorbing materials used, its environmental aspect coupled with a variety of its applications. The different existing performance and reliability evaluation models, sizing and control, grid connection and distribution have also been discussed. © 2011 Published by Elsevier Ltd.

Nanoparticles for photothermal therapies.

Abstract: The current status of the use of nanoparticles for photothermal treatments is reviewed in detail. The different families of heating nanoparticles are described paying special attention to the physical mechanisms at the root of the light-to-heat conversion processes. The heating efficiencies and spectral working ranges are listed and compared. The most important results obtained in both in vivo and in vitro nanoparticle assisted photothermal treatments are summarized. The advantages and disadvantages of the different heating nanoparticles are discussed.

Copper selenide nanocrystals for photothermal therapy.

Abstract: Ligand-stabilized copper selenide (Cu2-xSe) nanocrystals, approximately 16 nm in diameter, were synthesized by a colloidal hot injection method and coated with amphiphilic polymer. The nanocrystals readily disperse in water and exhibit strong near-infrared (NIR) optical absorption with a high molar extinction coefficient of 7.7 × 107 cm–1 M–1 at 980 nm. When excited with 800 nm light, the Cu2-xSe nanocrystals produce significant photothermal heating with a photothermal transduction efficiency of 22%, comparable to nanorods and nanoshells of gold (Au). In vitro photothermal heating of Cu2-xSe nanocrystals in the presence of human colorectal cancer cell (HCT-116) led to cell destruction after 5 min of laser irradiation at 33 W/cm2, demonstrating the viabilitiy of Cu2-xSe nanocrystals for photothermal therapy applications.

Advanced Thermoelectric Design: From Materials and Structures to Devices

Abstract: The long-standing popularity of thermoelectric materials has contributed to the creation of various thermoelectric devices and stimulated the development of strategies to improve their thermoelectric performance. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics, including structural design (point defects, dislocations, interfaces, inclusions, and pores), multidimensional design (quantum dots/wires, nanoparticles, nanowires, nano- or microbelts, few-layered nanosheets, nano- or microplates, thin films, single crystals, and polycrystalline bulks), and advanced device design (thermoelectric modules, miniature generators and coolers, and flexible thermoelectric generators). The outline of each strategy starts with a concise presentation of their fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of thermoelectric materials and devices. Overall, this review will serve to help materials scientists, chemists, and physicists, particularly students and young researchers, in selecting suitable strategies for the improvement of thermoelectrics and potentially other relevant energy conversion technologies.