Nguyen Tam Nguyen Truong

Synthesis and thermal annealing treatment of octylphosphonic acid-capped CdSe-tetrapod nanocrystals for bulk hetero-junction solar cell applications

CdSe-tetrapod nanocrystals (NCs) were synthesized by using octylphosphonic acid (OPA) as a capping ligand and cadmium oxide (CdO) as a cadmium precursor. The effects of thermal annealing in nitrogen (N2) environment on the chemical composition, morphology, crystal structure and optoelectronic properties of the CdSe-tetrapods have been investigated. Remarkable difference in the morphological and optoelectronic properties between as-synthesized and N2-annealed CdSe NCs was observed. The photoluminescence (PL) peak of N2-annealed CdSe NCs shifted to lower energy and UV-vis absorption spectra shifted to longer wavelength, indicating the size increase and improvement of the crystallinity of the CdSe tetrapods. The power conversion efficiency of bulk hetero-junction solar cells made with the annealed CdSe NCs showed higher value compared with the efficiency of cells made with as-synthesized CdSe NCs.

Structural and Optoelectronic Properties of CdSe Tetrapod Nanocrystals for Bulk Heterojunction Solar Cell Applications

Semiconducting CdSe tetrapod nanoparticles were prepared, and their structural and optical properties were examined. The surface capping molecule, octylphosphonic acid, was replaced with butylamine after the particle synthesis. The exchange of surface ligands changed the physical properties of the nanocrystals, which resulted in a slight decrease in the nanoparticles size. The effects of changing surface ligands of CdSe tetrapod nanocrystals on the structural and optoelectronic properties were investigated, and it was found that the surfactant of nanoparticles could affect the device performance by enhancing the charge carrier separation at the active layer interfaces. Power conversion efficiency of the bulk heterojunction solar cells having the structure of glass/ITO/PEDOT:PSS/(CdSe

Study of MEH–PPV/PCBM active layer morphology and its application for hybrid solar cell performance

Surface morphologies of MEH–PPV:PCBM active layers were optimized by investigating ITO substrate treated with oxygen and nitrogen plasma. This treatment effectively improved smoothness, transmittance, and contact angle of ITO’s, resulting in good anode contacts for hybrid device structures. The consistently improved performance of hybrid solar cells was also achieved. The surface properties of treated and untreated ITO substrates were compared by contact angle, four point probe, scanning electron microscopy, and atomic force microscopy.

Effect of post-synthesis annealing on properties of SnS nanospheres and its solar cell performance

SnS nanospheres (NSPs) were synthesized, and the effects of thermal annealing on the structural, morphological, chemical compositional and optical properties were examined. As-synthesized SnS NPSs with a mean size of 3-4 nm underwent a solid state morphological transformation by high temperature annealing in a nitrogen environment. Upon annealing, the size of SnS NSP increased to 5-6 nm with enhanced crystallinity. Also, the photoluminescence (PL) of the nitrogen-annealed samples slightly decreased in intensity with accompanying red-shift in spectrum. The power conversion efficiency of the solar cells using a polymer and the SnS NSPs was ~0.71%. These results confirm that the SnS NSPs demonstrate a potential as an inorganic material to be used in organic-inorganic hybrid bulk heterojunction (BHJ) photovoltaic devices.

Synthesis and characterization of tin disulfide nanocrystals for hybrid bulk hetero-junction solar cell applications

SnS2 nanoparticles (NPs) were synthesized using a modified hot injection method, and the morphological, structural, optical properties and chemical composition of the SnS2 NPs were characterized using a range of analysis techniques. Transmission electron microscopy (TEM) revealed distorted-hexagonal shape and particle size of the assynthesized nanoparticles. X-ray diffraction (XRD) showed that the SnS2 NPs had high crystallinity with hexagonal structure. Ultravioletvisible (UV-vis) absorption spectrum revealed an absorption band at 440nm due to SnS2 nanoparticles. Solar cell devices based on the blending of a conjugated polymer as a donor material and SnS2 (NPs) as an acceptor material were fabricated, and the device performance was tested. The solar cell efficiency was improved by optimizing the thickness of active layer containing the well-controlled SnS2 NPs, and increasing the light harvesting using a low band gap polymer. The results indicate that the SnS2 NPs can be good candidate materials for bulk hetero-junction (BHJ) solar cells.

Enhancement of CdSe/Poly(3-hexylthiophene) Bulk Heterojunction Solar Cell Efficiency by Surface Ligand Exchange and Thermal Treatment

Bulk heterojunction solar cells were fabricated by blending semiconducting cadmium selenide nanoparticles with various capping ligands and regioregular poly(3-hexylthiophene). The effects of surface ligand modification of CdSe nanoparticles and thermal treatment of fabricated cells on the device performance were investigated. It was found that surface ligands of nanoparticles could affect the device performance by increasing the charge carrier separation at the nanoparticle/polymer interface by quenching photoluminescence. Thermal treatment of fabricated cell structure at 140 °C was found to be optimal for device performance, resulting in a maximum power conversion efficiency of 1.17% under AM1.5G simulated solar irradiation.

Structural, morphological, and optoelectronic properties of rod-like iron pyrite nanocrystals for solar cell applications

Semiconducting, octadecylamine (ODA)-capped, rod-like FeS2 nanocrystals (NCs) are prepared and their properties are characterized. Transmission electron microscopy studies revealed the lattice fringes were clearly visible, confirming that the rod-like FeS2 NCs obtained in this study were highly crystalline. X-ray diffraction (XRD) studies indicated that the structure of FeS2 NCs is in cubic phase. Optical properties showed that the FeS2 NCs can be a promising candidate for the electron acceptor material in the bulk hetero-junction (BHJ) solar cell applications. The power conversion efficiency of the BHJ solar cells using polymer and the rod-like FeS2 NCs with a structure of glass/ITO/PEDOT:PSS/(FeS2+polymer)/Al was found to be ~0.45%.

Synthesis and characterization of CdSe nanocrystals in the presence of butylamine as a capping agent

TOPO-capped cadmium selenide (CdSe) nanocrystals of sizes between 3 and 8 nm have been synthesized, and the surface-capping molecule, trioctylphosphine oxide, was replaced by butylamine. The effects of changing the surface ligands of the synthesized CdSe nanocrystals on the structural, optical, and electrical properties were investigated. The shift toward shorter wavelength (higher energy) in the visible range of the optical absorption band edge was observed by UV-Vis spectroscopy, and a blue-shift of the photoluminescence peaks was observed with luminescent quenching. Surface modification was found to cause an increase in the surface energy of nanocrystals, resulting in the improvement in charge carrier separation and cell performance in applications towards bulk hetero-junction solar cells.

Effect of sulfur annealing on the morphological, structural, optical and electrical properties of iron pyrite thin films formed from FeS2 nano-powder

Iron pyrite (FeS2) thin films were fabricated by spin coating the solution of FeS2 nanocrystals of ∼40 nm in size on glass substrates, followed by annealing in a sulfur environment at different temperatures. The effect of sulfurization temperature on the morphology, structural, optical and electrical properties was investigated. With increase of the sulfurization temperature, the grain size and crystallinity of the films was improved, although some cracks and voids were observed on the surface of thin films. The band gap of the FeS2 films was decreased at higher sulfurization temperature. The electrical properties were also changed, including the increasing in resistivity and the decrease in Hall mobility, with increase of sulfurization temperature. The change in the optical and electrical properties of the FeS2 thin films was explained based on the changes of phase, morphology, surface, and grain boundary property.

Bulk Heterojunction Solar Cell Devices Prepared with Composites of Conjugated Polymer and Zinc Oxide Nanorods

ZnO nanorods (Nrods) with ~20ź50źnm lengths were synthesized using an aqueous solution of zinc acetate and glacial acetic acid. Bulk heterojunction solar cells were fabricated with the structure of indium tin oxide (ITO)/polyethylenedioxythiophene doped with polystyrene-sulfonic acid (PEDOT:PSS)/ZnO-Nrods + polymer/electron transport layer (ETL)/Al. Current density-voltage characterization of the resulting cells showed that, by adding an ETL and using polymers with a low band gap energy, the photoactive layer surface morphology and the device performance can be dramatically improved.