Minwu Song

Vertically Aligned ZnO Nanorods on Hot Filament Chemical Vapor Deposition Grown Graphene Oxide Thin Film Substrate: Solar Energy Conversion

Vertically aligned zinc oxide (ZnO) nanorods (NRs) were grown by the low-temperature hydrothermal method on graphene oxide (GO) coated FTO substrates, where GO was directly deposited on fluorine doped tin oxide (FTO) substrates using hydrogen (H(2), 65 sccm) and methane (CH(4), 50 sccm) through hot filament chemical vapor deposition (HFCVD) technique. The vertically aligned ZnO NRs were applied as effective photoanode for the fabrication of efficient dye sensitized solar cells (DSSCs). Highly uniform ZnO NRs were grown on GO deposited FTO substrate with the average length of ∼2-4 μm and diameter of ∼200-300 nm. The possible mechanism of grown ZnO NRs clearly revealed the significant role of GO on FTO in architecting the aligned growth of ZnO NRs. The grown vertically aligned ZnO NRs possessed a typical wurtzite hexagonal crystal structure. The structural and the optical studies confirmed the formation of partial hydrogen bonding between surface functional groups of GO and ZnO NRs. A solar-to-electricity conversion efficiency of ∼2.5% was achieved by DSSC fabricated with ZnO NRs deposited on graphene oxide (GO-ZnO NRs) thin film photoanode. The presence of GO on FTO substrate expressively increased the surface area of GO-ZnO photoanode, which resulted in high dye loading as well as high light harvesting efficiency and thus ensued the increased photocurrent density and the improved performance of DSSCs.

Iodine doped polyaniline thin film for heterostructure devices via PECVD technique: Morphological, structural, and electrical properties

AbstractThe deposition of undoped and iodine (I2)-doped polyaniline (PANI) on TiO2 thin film was carried out using plasma-enhanced chemical vapor deposition (PECVD) under different power inputs for the fabrication of p-polyaniline/n-TiO2 heterostructure devices. The increment in the size of TiO2 nanoparticles was observed after I2 doping by PECVD. The crystalline properties were altered upon I2 doping, suggesting a subtractive interaction between PANI and I2 moieties during PECVD. The significant changes in the structural and optical properties confirmed the I2 doping of PANI with strong bonding to the TiO2 nanomaterials. The existence of hydrogen bonding between the imine (-NH) of PANI and the hydroxyl (-OH) group of TiO2 nanomaterials was investigated by X-ray photoelectron spectroscopy characterization. A device fabricated by PANI/TiO2 or I2-PANI/TiO2 thin film with a top platinum (Pt) layer exhibited nonlinear behavior of current (I)-voltage (V) curve, i.e., moderate diode behavior. Compared to the Pt/PANI/TiO2 heterostructure device, the Pt/I2-PANI/TiO2 heterostructure device showed improved I–V properties with a considerably higher current of 0.050 mA, which might be attributed to the I2 doping-induced generation of large numbers of polarons in the PANI bandgap.

Metal Oxide Nanomaterials, Conducting Polymers and Their Nanocomposites for Solar Energy

The increasing concern on energy and the global warming due to the depletion of fossil fuel demands to search the alternative renewable energy resources for covering the energy crisis in the coming decade. A very popular renewable source called photovoltaic device is antici‐ pated to solve energy problem, which converts directly the solar energy from sun to the electricity energy. Recently, dye sensitized solar cells (DSSCs) are widely used as promising photovoltaic device owing to its important properties like high solar to electricity energy conversion efficiency, low production cost, ease of fabrication and vast varieties of various semiconducting materials. DSSC is composed of few micrometer-thick nanocrystalline semiconducting oxides thin film combined with monolayer of charge-transfer dye as a photoanode, a redox electrolyte and a platinum metal electrode as counter electrode. In principle, upon illumination, the electron injection to conduction band of semiconductor takes place by the absorption of photons from dye molecules and the redox electrolyte regenerates the oxidized dye by the transportation of charges or ions. These days, the photovoltaic devices are facing inherent drawbacks such as leakage and evaporation problem that limits its practical application. In this regards, efforts are being done to overcome the leakage and evaporation of liquid electrolyte with solid or gel electrolytes such as room temperature molten salts (RTMSs), p-type semiconductor, conducting organic polymers and polymer gel electrolytes. Furthermore, the choice of catalytic in counter component of DSSCs is crucial to improve the reduction rate of I3 to Iin the redox electrolyte. In general, the conducting glass electrode without any catalytic materials such as metals, conducting polymers etc shows very low electrocatalytic activity towards the iodide couple electrolyte due to overvoltage and high energy loss. It has been realized that the low resistance and high electrocatalytic materials

Effect of Al concentration on photoluminescence properties of sol-gel derived hydrogen annealed ZnO

The effect of the Al/Zn atomic ratio on the photoluminescence properties of hydrogen annealed undoped and Al rich ZnO (AZO) films was studied. The Al/Zn atomic ratios in the AZO films were varied from 0 to 40%. All the AZO films exhibited three peaks in the UV, green and red regions, whereas the undoped ZnO films had two peaks in the UV and green regions. The PL intensity in the UV and red regions increased with an increase in Al concentrations. The highest PL intensity in the UV region was observed in the 20% Al/Zn atomic ratio due to improvement in crystal quality which was also confirmed by XRD measurements. The PL emission in the red region was due to complex luminescent centers like (Vzn-Alzn)−. A blue shift was seen in the red region with the introduction of Al. The 20% AZO films obtained the strongest signal at −420 cm−1, whereas no FTIR signal was observed at 420 cm−1 in undoped ZnO. The bond signature at −420 cm−1 might be responsible for the highest PL intensity in NBE and red regions.