Priyanka U. Londhe

CuInSe2 thin film solar cells prepared by low-cost electrodeposition techniques from a non-aqueous bath

Polycrystalline CuInSe2 (CIS) thin films have been prepared by low-cost electrochemical method from non-aqueous ethylene glycol solvent onto cadmium sulfide (CdS) thin films. The co-deposition potential for Cu, In and Se was optimized with cyclic voltammetry measurements. CIS layers were electrodeposited at −1.1, −1.3 and −1.5 V versus Ag/AgCl references in an air-tight custom made electrodeposition cell. The films were selenized at 400 °C for 20 minutes. The optical, structural, morphological, compositional and optoelectronic properties of as-prepared and selenized samples were studied using UV-Vis spectrophotometery, X-ray diffractometery, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and current–voltage (I–V) measurements. Three prominent sharp peaks of tetragonal CIS, (112), (204)/(220), and (312/116) were revealed in all as-prepared and selenized samples. Upon selenization the crystallinity of the samples was found to be improved remarkably. Compact, void free, and nearly uniform thin films of grain size ∼1 μm were deposited. The as-deposited and selenized CIS samples were Cu-rich whereas the content of Se was ∼50% obtained by EDAX analysis. The value of inter-planer distance, d = 3.339 A, measured by HRTEM corresponds to the (112) plane of a tetragonal CIS crystal structure. The circular spotted rings observed in the selected area diffraction (SAD) pattern were confirmed as (112), (204)/(220) and (312)/(116) reflections of CIS. The solar cell parameters, Voc, Jsc, FF and efficiency (η) were found to be 303 mV, 28 mA cm−2, FF ∼ 53% and η = 4.5% for the CIS film deposited at −1.5 V. The values of shunt conductance, GD = 2.5 mS cm−2 and GL = 7.9 mS cm−2 and series resistance, RD = 0.81 Ω cm2 and RL = 0.19 Ω cm2 were calculated for dark and illuminated conditions. Mott–Schottky analysis was also carried out on the final solar cell in dark and illuminated conditions to study the carrier concentration and defects in the CdS/CIS interface.

Electropolymerization of polyaniline thin films

Polyaniline (PANI) thin films have been electrochemically synthesized onto conducting glass substrates. The current study demonstrates that the properties of PANI films depend on the concentration of dopant acid. Well-adherent PANI coatings were obtained under potentiodynamic conditions during sequential scanning of the potential region between −0.35 V and +1.7 V with respect to silver/silver chloride. The structural, optical, and morphological properties of PANI films were studied with the aid of X-ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible (UV-Vis) absorption spectroscopy, photoluminescence (PL) spectroscopy, and field-emission scanning electron microscopy (FESEM). Current–voltage (I-V) measurements were performed to study the electrical properties of PANI films. The XRD peaks observed at 2θ = 15.4°, 24.2°, and 25.1° confirm the synthesis of emeraldine form of PANI. The strong absorption peaks observed in the UV-Vis absorption spectra at 317 nm (π–π* interband transition), 371–427 nm (polaron band transition), and 750 nm (bipolaron band transition) confirm the formation of emeraldine oxidation state of PANI. A broad peak attributed in the PL spectra around 395 nm is related to the transition from polaronic band to the π band. All the intense bands attributed in the Raman spectra are associated with the emeraldine oxidation state of PANI. FESEM images reveal the formation of fibers and belts of PANI. Highly conducting thin films of PANI deposited at higher concentrations of dopant acid were confirmed by I-V measurements.

Electrochemically synthesized CuInSe2 thin films from non-aqueous electrolyte for solar cell applications

Highly polycrystalline CuInSe2 (CIS) thin films have been electrodeposited from non-aqueous ethylene glycol (EG) solvent on fluorine-doped tin-oxide-coated glass substrates at 130 °C. The co-deposition potential for Cu, In and Se was optimized by using cyclic voltammetry. CIS layers have been electrodeposited from −1.1 V to −1.5 V versus the Ag/AgCl reference electrode. The effect of selenization on structural, morphological, optical and compositional properties has been studied extensively. Highly crystalline CIS thin films are electrodeposited for all reported growth potentials without post-annealing treatment. The Raman spectra of stoichiometric CIS thin films showed a dominant A1 mode with features receptive to the crystalline quality of the layers. Noticeable changes in the surface morphology and composition of films deposited at different deposition potential were observed. All CIS layers were void free, compact, uniform, and well adherent to the substrates with particle size ~1–3 μm. Both as-deposited and selenized samples were Cu-rich, however, the composition of selenium remained closer to the ideal value, 50%. A typical solar cell prepared at −1.3 V measured V OC = 0.316 V, J SC = 26 mA, FF = 49, and η = 4.2, under illuminated conditions at 100 mW cm−2.

Influence of capping agents on the growth of gold nanoparticles from aqueous and non-aqueous medium

Gold nanoparticles (Au NPs) with different shape and size were prepared in an aqueous and non-aqueous solution using cetyltrimethylammonium bromide (CTAB) and poly(vinylpyrrolidone) (PVP) as a capping agent by simple chemical synthesis. In an aqueous bath Au NPs were synthesized at room temperature and high temperature was found to be suitable for non-aqueous bath. These Au NPs are characterized by using different characterization techniques. Effect of capping agent on the particle size and shape for different medium were extensively studied using UV-Vis spectroscopy and transmission electron microscopy (TEM).

Effect of Annealing on Undoped and Al‐ doped Zinc‐oxide Thin Films Prepared By Sol‐Gel Method

The nanocrystalline undoped and Al‐ doped zinc oxide (ZnO:Al) thin films were deposited on quartz substrate by sol‐gel method. The effect of Al‐doping along with the heat treatment on undoped & Al‐doped ZnO thin films was extensively studied. The ZnO:Al thin films were preferentially c‐axis oriented, the effect became more prominent after the heat treatment. Optical properties were studied by using UV‐Vis‐NIR spectrometer and Photoluminescence (PL) spectrophotometer. Atomic force micrograph revealed compact, void free & uniform deposition of both ZnO & ZnO:Al films.

Synthesis and Characterization of Controlled Size CdSe Quantum Dots by Colloidal Method

Monodispersed and highly luminescence cadmium selenide (CdSe) quantum dots (QDs) have been prepared in a single pot by colloidal reaction method. The QDs were characterized using X-ray diffraction (XRD), Raman Spectroscopy, transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), UV-visible absorption spectroscopy and photoluminescence (PL) spectroscopy to study the structural, morphological, compositional and optical properties. The growth temperature played an important role to control the particle size. The optical wavelength was found to be shifted systematically from 460 nm to 575 nm upon increasing the reaction temperature from 110 °C to 260 °C. The size of CdSe QDs, ~2-4 nm was estimated from absorption data. The emission tail exhibited at higher wavelength in PL measurement for the QDs synthesized for lower reaction temperature revealed the presence of surface trap-states. A cubic crystal structure of CdSe QDs was revealed by XRD analysis. The spherical QDs of size 2 to 4.5 nm were observed from TEM analysis for the samples prepared at 140 °C, 200 °C and 260 °C. The sizes of QDs obtained by TEM are in good agreement with the results obtained from optical and XRD data. High resolution transmission electron microscopy (HRTEM) confirmed the cubic crystal structure of CdSe QDs. The Selected area diffraction (SAD) pattern exhibited diffused ring corresponds to (111), (220) and (311) reflections of cubic structure of CdSe. The compositional analysis studied by EDS revealed the growth of nearly stoichiometric CdSe QDs. The LO1 vibrational mode observed about 202-205 cm-1 decreases the broadening systematically upon increasing the reaction temperature.

Effect of oxidizing agent on the properties of polyaniline thin films

Conducting polymers have been widely investigated because of their fascinating electrical and optical properties. In the present work, the oxidation of aniline was carried out in acidic aqueous media using chemical bath deposition method. Aniline, hydrochloric acid and ammonium dichromate (ADC) are used as aniline oligomers, dopant acid and oxidizing agent, respectively. Effect of oxidizing agent concentration on various properties of polyaniline thin films were studied extensively with the aid of Raman spectroscopy, UV-Vis spectroscopy, PL spectroscopy, scanning electron microscopy and current-voltage measurements. UV, PL and Raman studies reveals that the higher concentration of ADC leads to the formation of emeraldine base form of PANI and at lower concentration supports the growth of conducting emeraldine salt. SEM micrographs confirm the compact and uniform growth of PANI. PANI films grown at lower concentration of ADC shows higher conductivity.