Azimah Omar

Morphological and electron transport studies in ZnO dye-sensitized solar cells incorporating multi- and single-walled carbon nanotubes

Dye-sensitized solar cells (DSSCs) incorporating zinc oxide (ZnO) nanostructures and carbon nanotubes (CNTs) were fabricated using a chemical bath deposition method. The nanoflake structures captured by a field-emission scanning electron microscopy analysis traced the appearance of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) in the photoanode thin film. The photovoltaic performance of the photoanode was quantified by means of an electrochemical impedance spectroscopy (EIS) unit with GAMRY-Physical Electrochemistry. The ZnO?SWCNT-based DSSC exhibited good photovoltaic performance with power conversion efficiency (?), photocurrent density (Jsc), open-circuit voltage (Voc) and fill factor (FF) of 1.31%, 15.31?mA?cm?2, 0.224?V and 0.36, respectively. The EIS unit was also employed to quantify the charge transport resistance (Rct), transport resistance (Rt) and effective electron lifetime (?eff) of the DSSC. The impedance analysis of the ZnO?SWCNT-based DSSC also determined greater highly efficient electron transport due to long effective electron diffusion length than the film thickness of the photoanode.

Platinum-Incorporating Graphene Counter Electrode for In2O3-Based DSSC with Various Annealing Temperatures

Development of platinum incorporating graphene (pt/graphene) thin films was prepared by sol-gel method via chemical bath deposition (CBD). Indium oxide (In2O3) as photoanode and pt/graphene as counter electrode is used to analyse the characteristics and performance of dye-sensitized solar cell (DSSC). Different annealing temperatures of 200 oC, 250 oC and 300 oC were proposed for the counter electrode in this study. The changes in the structural properties were analyzed by means of X-ray Diffraction (XRD) and atomic force microscopy (AFM) analysis. AFM results indicated very rough surface area of graphene sheet where roughness values decreased linearly from 0.65 μm to 0.18 μm by an increment in annealing temperature. The In2O3-based DSSC exhibited good photovoltaic performance with power conversion efficiency (η), photocurrent density (Jsc), open circuit voltage (Voc) and fill factor (FF) of 0.47 %, 5.46 mA cm-2, 0.54 V and 0.36 respectively. The obtained structural and photovoltaic performance analysis was proposed as a suitable benchmark for pt/graphene counter electrode with In2O3-based DSSC.

Structural, Morphological, Photovoltaic and Electron Transport Properties of ZnO Based DSSC with Different Concentrations of MWCNTs

This study highlights the structural, morphological, photovoltaic and electron transport properties of zinc oxide-multi-walled carbon nanotubes (ZnO-MWCNTs) based dye-sensitized solar cell (DSSC) prepared at different concentrations of 0.0, 0.1, 0.3 and 0.5 wt.%. The ZnO-MWCNTs thin films were prepared by a chemical bath deposition method. X-ray diffraction (XRD) analysis proved the formation of hexagonal wurtzite of the samples. The crystallite sizes, D of ZnO-MWCNTs was measured varies from 21 nm to 11 nm. The oat-like ZnO nanoflakes structure and the presence of MWCNTs were captured by field-emission scanning electron microscopy (FESEM) analysis. Transmission electron microscopy (TEM) analysis measured the inner (~6.81 nm) and outer (~28.31 nm) diameter of MWCNTs. The optimum concentration of 0.1 wt.% MWCNTs produced the highest photocurrent density, Jsc of 13.5 mA/cm2, open-circuit voltage, Voc of 0.149 V, fill factor, FF of 0.406 and power conversion efficiency, PCE of 0.817 %. Optimum doping of 0.1 wt.% MWCNTs generated short electron lifetime, τeff of 0.67 ms, low effective electron chemical diffusion coefficient, Deff of 9.5 x 10-8 cm2 s-1 and higher electron recombination rate, keff of 1497.48 s-1. The addition of MWCNTs has influenced the structural, morphological, photovoltaic and electron transport properties of ZnO-MWCNTs based DSSC.

Effect of Heat Treatment on CNT/TiO2 Photoelectrode for Dye-Sensitized Solar Cells Application

In this research, the CNT/TiO2 nanocomposite solution was prepared using sol-gel method process. Definite amounts of CNT (0.06 g) were sonicated in 30 ml anhydrate 2-propanol. The measured quantities of Titanium (IV) Tetraisopropoxide (TTIP) – 5 ml were introduced into the CNT/2-propanol solution. The CNT/TiO2 paste was doctor-bladed onto the FTO glass and consequently annealed at 250 °C, 350 °C and 450 °C for 30 min. The effect of annealing temperatures on the CNT/TiO2 thin films was discussed. The CNT/TiO2 thin films were characterized for morphological and electrical performance by Field Emission Scanning Electron Microscopy (FESEM), X-ray Diffraction (XRD), Incident Photon to Charge Carrier Efficiency (IPCE) and IV-Curve Efficiency analysis. The XRD patterns show the thin films major peak at (101) with average anatase phase crystallite size. The CNT/TiO2 thin films morphological structure composed of compressed and porous distributed composition. The crystal structures were changed upon increasing the annealing temperature. The IV measurement shows that the dye-sensitized solar cell (DSSC) at 450 °C produced highest photoelectric conversion efficiency (η) with 3.88 %. IPCE graph shows the solar cell absorb light within the UV spectrum region. It is revealed that annealing temperature has influence toward photovoltaic performance of the assembled DSSC.

Influence of Graphene (0.01 wt. %) on Structural, Morphological and Photovoltaic Properties of TiO2-Based DSSC Using Electrolyte Gel

Titanium dioxide (TiO2) based dye-sensitized solar cells (DSSCs) doped with reduced graphene oxide, rGO also known as graphene were fabricated at concentrations of 0.01 wt.% . The performance of TiO2/graphene based DSSC and TiO2 based DSSC were studied using electrolytes; PAN-based gel electrolyte. The thin films were characterized using several characterizations such as scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and current-voltage (I-V) measurement. The micrograph images obtained by SEM demonstrated that the thin films are highly porous. The XRD characterization showed that the crystalline particle of thin films is an anatase state and high percentage of carbon composition can be determined using EDX analysis. Through I-V characteristic, the current density Jsc, open circuit-voltage Voc, fill-factor FF, and efficiency η of the TiO2-based DSSC were 0.196 mA/cm2, 0.44 V, 0.496 and 0.043% respectively. I-V characteristic showed an increase in values for rGO/TiO2 based DSSC such as Jsc = 1.177 mA/cm2, Voc = 0.66 V, FF = 0.656 and η = 0.509%. The addition of rGO concentration has improved the efficiency of DSSC while the use of electrolyte gel can sustain the stability of the cell.

Growth and Structural Properties of ZnO-SWCNTs Produced by Chemical Bath Deposition and Sol-Gel Methods

Two different methods were used to synthesize and fabricate zinc oxide-carbon nanotubes (ZnO-CNTs) thin films; chemical bath deposition (CBD) and sol-gel method. Single-walled carbon nanotubes (SWCNTs) were implemented in preparing the thin films. The obtained thin films were annealed in air at different temperatures levels of 200 °C, 250 °C, 300 °C and 350 °C for 30 min. Both methods successfully grew various nanostructures of ZnO-CNTs such as nanoparticles, nanobranches and nanoflakes. The synthesized nanostructures were characterized by using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The crystallite sizes were calculated between 38.54 nm and 6.13 nm. FESEM cross sectional images indicated the thin film thicknesses varied from 164.9 μm to 5.84 μm. The TEM images estimated the diameters of the SWCNTs in the range of 3.38 nm to 16.14 nm. TEM images also proved the presence of ZnO entangled between SWCNTs. A combination of ZnO and SWCNTs in the thin film proposes a simple and low cost CBD method to produce various ZnO-CNTs nanostructures with appropriate thickness. Keywords: zinc oxide; carbon nanotubes; nanostructures; thin film ABSTRAK Dua kaedah telah digunakan untuk mensintesiskan serta memfabrikasi filem nipis zink oksida-karbon nanotiub (ZnO-CNTs); kaedah pemendapan kubang kimia (CBD) dan sol-gel. Karbon-nanotiub berdinding satu (SWCNTs) telah digunakan dalam penyediaan filem nipis. Filem nipis yang diperolehi disepuh-lindap melalui udara pada tahap suhu yang berbeza dari 200 °C, 250 °C, 300 °C dan 350 °C selama 30 minit. Kedua-dua kaedah telah berjaya menumbuhkan pelbagai struktur nanoZnO-CNTs seperti nanozarah, nanodahan dan nanokepingan. Pencirian struktur nanoitu dilakukan menggunakan mikroskop elektron imbasan (FESEM), belauan sinar-X (XRD) dan mikroskop electron pancaran (TEM). Saiz kristal yang dikira adalah antara 38.54 nm dan 6.13 nm. Analisis bagi keratan rentas FESEM imej menunjukkan ketebalan filem yang pelbagai dari 164.9 μm sehingga 5.84 μm. Imej TEM menganggarkan diameter karbon nanotiub dalam julat 3.38 nm sehingga 16.14 nm. Imej TEM turut mengesahkan kewujudan ZnO yang melekat di antara CNTs. Kombinasi ZnO dan SWCNTs di dalam filem nipis mencadangkan penggunaan kaedah CBD yang ringkas dan berkos murah untuk menghasilkan pelbagai struktur ZnO-CNTs bersaiz nanodengan ketebalan yang sesuai. Kata-kata kunci: zink oksida; karbon nanotiub; struktur bersaiz nano; filem nipis