Mohd Hanapiah Abdullah

Thickness-Dependent Characteristics of Aluminium-Doped Zinc Oxide Nanorod-Array-Based, Ultraviolet Photoconductive Sensors

Aluminium (Al)-doped zinc oxide (ZnO) nanorod arrays were prepared on a seed-layer-coated glass substrate by a sonicated sol–gel immersion method. We have shown, for the first time, that the thickness of the nanorod arrays can be increased incrementally without greatly affecting the diameter of the nanorods, by increasing the number of immersions. The field-emission scanning electron micrographs and thickness measurements revealed that the nanorods had diameters within the range from 40 to 150 nm and thicknesses from 629 to 834 nm with immersion times ranging from 1 to 5 h. The photoluminescence (PL) spectra revealed that the ZnO nanorod quality was enhanced with long immersion times as shown by an improvement in the ratio of the UV peak intensity to the visible emission peak intensity, or IUV/Ivis. The thickness-dependent characteristic of Al-doped ZnO nanorod-array-based, UV photoconductive sensors was studied; minimising the thickness of the nanorod arrays was found to provide high responsivity and good performance. Our experiments showed that a decrease in the thickness of the nanorod arrays improved the responsivity and response time of the UV sensors, with a maximum responsivity of 2.13 A/W observed for a 629-nm-thick nanorod film.

Optical Properties and Surface Morphology of PMMA: TiO2 Nanocomposite Thin Films

Sol-gel spin coated PMMA:TiO2 nanocomposite thin films on glass substrates were studied by comparing two types of the sol-gel solutions. Two types of PMMA:TiO2 nanocomposite sol-gel solutions were prepared; one using Degusa (P25), and the other one is using self-prepared TiO2 powder. The self-prepared nanosized TiO2 powder is obtained by drying the TiO2 sol-gel using solvothermal method followed by grinding the TiO2 crystal using ball miller. Triton-X was used as surfactant to stabilize the composite. Besides comparing the nanocomposite solution, we also studied the effect of the thin films thickness on the optical properties and their surface morphology. The optical properties and surface morphology were measured with UV-VIS spectrometer and atomic force microscopy (AFM). The result showed that nanocomposite PMMA with self-prepared TiO2 give high optical transparency than that of with Degusa (P25). The results also indicate that as the thickness is increased the optical transparency are decreased. Both AFM images showed that the agglomerations of TiO2 particles occurred on top of the thin film and the surface roughness increased when the thickness is increased. AFM results show that nanocomposited PMMA with P25 has high agglomeration particles compared to the other one.

Effect of Solvent on the Dielectric Properties of Nanocomposite Poly(methyl methacrylate)-Doped Titanium Dioxide Dielectric Films

A poly(methyl methacrylate)-doped titanium dioxide (PMMA:TiO2) nanocomposite film was obtained by spin coating the nanocomposite solution onto a silicon substrate. The nanocomposite solutions were prepared by dissolving the PMMA and TiO2 nanopowder in three different types of organic solvent, namely, toluene, tetrahydrofuran (THF), and acetone. We found that the dielectric properties of the PMMA:TiO2 nanocomposite are dependent on the type of solvent used. The dielectric properties measured at a frequency of 1 kHz showed that acetone gives the highest dielectric constant and capacitance compared with toluene and THF. Toluene gives the lowest dielectric loss among the three. The topography and roughness of the PMMA:TiO2 nanocomposite indicate that a particular solvent results in a different kind of surface morphology.

The Photovoltaic Performance of Doped-CuI Hole Conductors for Solid State Dye-Sensitized Solar Cells

The iodine doped copper (I) iodide (I2: CuI) at different weight of iodine dopant have been prepared to investigate its thin films properties and photovoltaic performance. A novel method of mist atomization technique has been used for the deposition of CuI materials. The structural and electrical properties of CuI thin films deposited on the glass substrates were studied. The thin films morphology examined by FESEM shows a variation of crystal size and structure. Brick-like structure with smooth faces and sharp edges were seen for the doped thin films. The CuI thin films at 30 mg of iodine doping shows the highest resistivity of 4.56 × 101 Ω cm which caused by the surface traps create by iodine doping. The photovoltaic performance of ss-DSSC on the effect of variation iodine doping was investigated. The ss-DSSC fabricated with undoped CuI materials shows the highest efficiency of 1.05% while the 40 mg I2 content shows the lowest conversion efficiency of 0.45%. The crystals size of CuI and its degree of crystallization are greatly contributed to the high filling fraction of the porous TiO2 layer and hence the cells performance.

Photoanode of nanostructured TiO 2 prepared by ultrasonic irradiation assisted of sol-gel with P-25 for dye-sensitized Solar Cells

In this work, TiO2 photoanode have been prepared by mixing the commercial titania powder P-25 with a titanium sol gel. In order to improve the mixing condition the paste was gone through the ultrasonic treatment. After that, the doctor blade technique was used to deposit TiO2 paste on ITO-coated glass substrate. There were two monolayer photoanodes with ultrasonic and without ultrasonic TiO2 pastes of about the same thickness have been prepared and their effects on the overall cell performances of the DSSC were compared. From the solar simulator measurement the solar energy conversion efficiency (η) of 2.6642% under AM 1.5 was obtained with the ultrasonic photoanode DSSC which correspond to the short-circuit photocurrent density (Jsc) and open-circuit voltage (Voc) of 7.2552 mA/cm2 and 0.5168 V, respectively, while 1.3127% conversion efficiency (η) obtained from without ultrasonic TiO2 photoanode. The TiO2 photoanode with ultrasonic were efficiently in the fabrication process of dye-sensitized solar cells (DSSCs), where the improvement which was almost double from unsonicated film for the overall energy conversion efficiency (η) that achieved for the sonicated TiO2 photoanode with the present of PEG.

Electrical properties of spin coated PMMA for OFETs applications

Poly (methy-methacrylate) (PMMA) thin films were deposited by sol-gel spin coating method on glass substrates. PMMA powder was dissolved in 60ml Toluene with the concentration of the PMMA in the solution was varied from 30 ∼ 120 mg. Besides the PMMA concentration, we also studied the effect of the thin films thickness on the electrical properties. The results for electrical properties showed that there is a difference of the I–V, resistivity, conductivity and the dielectric constant with different thickness. Conductivity of the PMMA thin film was found to ∼ 10−6 Ωcm and continue to decrease as the PMMA concentration increased. Pinholes were identified to be formed on the films with the higher density due to the increasing PMMA concentration.

Transmittance Enhanced Properties of Novel Encapsulated ITO/Arc-TiO2 Antireflective TCO Substrate Prepared by RF Magnetron Sputtering

In this work, a thermally stable multilayered transparent conducting oxide (TCO) utilizing TiO2 antireflection thin film (arc-TiO2) encapsulated under indium tin oxide (ITO) glass has been prepared by RF magnetron sputtering. The novel tri-functional conducting substrate with blocking layer capabilities has been designed via step-down interference coating structure of double layer antireflection coating (DLAR). The mixed-oriented type between the strongest ITO peak at (222) and a weak TiO2 peaks at (101) orientations have been observed under XRD analysis. The antireflection properties of double-layer ITO/arc-TiO2 is evidence with the existence of two maximum peaks around 410 nm and 750 nm. While, the corresponding reduction in reflectance of about 8% and 2% compared to bare ITO was achieved. The ITO/arc-TiO2 blocking layers conserves the low resistivity of ITO at 2.05 x 10-4 Ω cm, even after oxidizing during air annealing process above 400 °C. These results demonstrate that the multilayered ITO/arc-TiO2 with tailored refractive index by means of annealing treatment is a promising approach to realize a substrate which (a): electrically and thermally stable against processing temperature, (b): sustains the higher transmittance of the substrate even there is increase in total substrate thickness and (c): prevents electron recombination process occurring at the interface between the redox electrolytes and the TCO surface. The stable properties are found to be beneficial for use as TCOs in DSSCs.

The Influence of TiO2 Photoanode Morphology for Scattering Enhanced Properties of Dye-Sensitized Solar Cell

Effect of PEG on the TiO2 electrode morphology for scattering enhanced properties of the modified paste containing TiO2 sol-gel mixed with Degussa P-25 were investigated. The high surface area of the scattering centres in this study were formed by using nano size particles ascribed from TiO2 sol-gel while the sub-micron size particles were utilized from the reaction of PEG on the Degussa P-25 particles. The pore size distributions were tailored by varying the PEG content in the fabricated electrodes. Higher surface area with adequate pore size of P30 electrode has contributed to higher JSC and efficiency (η) of 11.35450 mA/cm2 and 2.479624 %, respectively. Photocurrent action spectra of IPCE of the DSSC exhibit the maximum of 42 % at 550 nm correspond to the P30 TiO2 electrode. Overall results suggest that the incorporation of TiO2 sol-gel component mixed with TiO2 paste derived from commercially available nanopowder could enhance surface area as well as serves for better light scattering effect, while PEG addition creates adequate pore size distribution to maximize the dye adsorbed on the TiO2 electrode.

Optical properties of nano-structured zinc oxide thin films deposited by radio-frequency magnetron sputtering at different substrate temperatures

ZnO thin films were deposited by Rf Magnetron sputtering on glass substrates at various deposition temperature in the range of 100-400°C. The thin films characterized using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and UV-VIS-NIR spectrophotometer for morphology and optical properties study. All the films are transparent in the visible region (400-800 nm) with average transmittance above 90 %. The optical transmittance and band gap energy, calculated from the spectra of optical absorbance, show a significant dependence on the growth temperature. As for the sample grown at 100°C, the average transmittance is about 90% in the visible wavelength range and the band gap is estimated to be 3.249 eV.

The fabrication of solid state dye-sensitised solar cells with I2 doped CuI as the hole conductors

The fabrication (ss-DSSC) were done by employing the iodine doped CuI (I2:CuI) as the hole conductors. The hole conductor deposition was done by varying the I2:CuI weight in order to investigate its effect to the device performance. The brick-like structure with smooth faces and sharp edges were seen for the doped thin films. The high electrical resistivity of I2:CuI thin films were observed compared to the undoped CuI thin films which is caused by the surface traps create by iodine doping. The ss-DSSC fabricated with undoped CuI hole transport layer shows the highest efficiency of 1.05% which is in a good agreement with the resistivity value of CuI thin films. The cell fabricated with 40 mg I2:CuI shows the lowest conversion efficiency of 0.45%. The crystals size of CuI and its degree of crystallisation are greatly affect the solar cells performance.