Mohd Fairus Ahmad
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Preferred name
Mohd Fairus Ahmad
Official Name
Mohd Fairus , Ahmad
Alternative Name
Shahimin, Mohd Faidz Mohamad
Mohamad Shahimin, M. F.
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Scopus Author ID
57006554500
Researcher ID
B-9547-2018

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The effect of solvents on the performance of organic light-emitting diodes

2020-01-08 , Ismail N.A.N. , Safizan Shaari , Juhari N. , Norhayati Sabani , Mohd Fairus Ahmad , Zakaria N.F.

In this paper, we investigate the solvent effect on the performance of surface roughness, absorption spectrum of MEH-PPV thin films and J-V characteristics for MEH-PPV OLED device. The 5 mg emissive layer of poly [2-methoxy-5(2' -ethylhexyloxy)-1, 4-phenylenevinylene), MEH-PPV was diluted with 1ml toluene and 1 ml different mixture of solvent (80% toluene+20 % chloroform) which gives the concentration of 5 mgml-1 respectively. The surface roughness of MEH-PPV film was reduced to 0.3 nm and the red-shifted maximum peak wavelength value were obtained when mixture solvent was used. However, J-V gives higher turn on voltage ∼17 V for the device used mixture solvent compared to device prepared by toluene solvent. Apparently, the two different combination of aromatic and non-aromatic solvent significantly gives an effect on thin films properties and electrical properties of MEH-PPV OLED device.

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Copper doping effect in the back surface field layer of CdTe thin film solar cells

2024-02-01 , Nur Irwany Ahmad , Kiong T.S. , Doroody C. , Rahman K.S. , Mohd Natashah Norizan , Mohd Fairus Ahmad , Kar Y.B. , Harif M.N. , Amin N.

In this work, the Solar Cell Capacitance Simulator (SCAPS-1D) is employed to evaluate the characteristics of CdTe thin films with ZnTe as the Back Surface Field (BSF) layer and estimate the effective copper doping ratio at both the atomic scale and the device operational response perspective. The electrical characteristics of ZnTe, at varying levels of copper doping, were derived using density functional theory (DFT) by applying the generalized gradient approximation (GGA) and Hubbard U corrections (DFT+U). The performance of ZnTe with different Cu concentrations as a BSF layer was evaluated by analysing the values of four key parameters that are open circuit voltage (VOC), short circuit current density (JSC), fill factor (FF), and conversion efficiency (η). The results indicate that an increase in Cu concentration from 0% to 3%, 6%, 10%, and 12% resulted in a reduction of the energy band gap. Specifically, the energy band gap decreased from 2.24 eV to 2.10 eV, 1.98 eV, 1.92 eV, and 1.88 eV, respectively. Optimal Cu doping promotes the favourable shift in the valence band maxima (VBM) and formation of p + -ZnTe, lowering thermionic emission and improving carrier lifetime, which results in an improved ohmic contact, η = 18.73% for 10% of Cu content. Excessive doping in contrast degraded the overall device performance by forming an unmatched carrier band offset at the front interface with CdS, increasing the acceptor type defect and CdTe compensation rate. Overall, the findings suggest that incorporating a controlled level of Cu, which in this case is around 10%, promotes the efficiency and stability of the proposed CdTe device configuration to a certain extent.

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The efficiency effect of dye sensitized solar cell using different ratio of organic polymer doped titanium dioxide at different annealing process temperature

2020-01-08 , Norhisamudin N.A. , Norhayati Sabani , Rosli N. , Mohd Fairus Ahmad , Juhari N. , Safizan Shaari , Zakaria N.

Titanium Dioxide (TiO2) is one of the main materials in Dye Sensitized Solar Cell (DSSC). It is well known with its property of good optical transmittance and its mesoporous surface that can absorb generous amount of dye. In this study, TiO2 is fabricated using spin coating technique that leads to the uniform thickness of TiO2 layer. The thickness of the TiO2 can be controlled layer by layer using same technique to get an optimized surface that can lead to better performance of DSSC. In order to achieve this, the surface roughness of TiO2 must be as high as possible. Therefore, the organic material which is Poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene-vinylene (MEH-PPV) is used as medium to increase the mesoporous roughness structure of TiO2 nanocrystal film for DSSC. MEH-PPV is doped into the TiO2 using 0.5 mg/ml with different temperatures of 100°C and 450°C. Different temperatures of MEH-PPV will lead to the different surface structures for TiO2 thin film. The ratio of TiO2:MEH-PPV used were 1:1 and 2:1. The surface of TiO2 thin film was characterized using Atomic Force Microscope (AFM). The efficiency was obtained using Solar Simulator based on the voltage and current flow. Based on the results, the increment of surface roughness is about 21% for the different ratio at various temperatures. The optimum temperature and suitable ratio of TiO2:MEH-PPV was obtained via annealing process at 450°C with the ratio of 2:1. It gives the highest efficiency which is 0.1266%. These two important findings yield good mesoporous surface of TiO2 thin film.

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Optimization of MEH-PPV Based Single and Double-Layer TOLED Structure by Numerical Simulation

2021-01-01 , Kersenan T. , Zakaria N.F. , Shaari S. , Norhayati Sabani , Juhari N. , Mohd Fairus Ahmad , Rahim A.F.A.

In this work, we simulated and characterized Poly [2-methoxy-5-(2’-ethylhexyloxy)-1, 4-phenylene vinylene] (MEH-PPV) based single and double-layer TOLED by using Silvaco ATLAS device simulator to achieve prominent values of electrical and optical properties of the device. MEH-PPV were used as the emitting layer (EML) in the single-layer, while addition of Poly [(3,4-ethylene dioxythiophene)-poly(styrene sulfonate)] (PEDOT-PSS) as the electron transport layer (ETL) were conducted in double-layer TOLED simulation. The EML and ETL thickness in both structures were varied between 10 – 150 nm, respectively, to observe and understand the underlying physics of the relation in the layer thickness to the electrical and optical characteristics. Furthermore, variation of the EML/ETL thickness ratio from 1:1 to 5:1 (with thickness in between 10 to 50 nm) had also been conducted. From this work, it is understood that the thickness of the EML layer plays the most important role in TOLED, and by balancing the carrier injections and recombination rate in appropriate EML/ETL thickness ratio, the electrical and optical properties can be improved. By optimizing the EML/ETL thickness and thickness ratio, an optimal forward current of 1.41 mA and luminescent power of 1.93e-18 W/μm has been achieved with both MEH-PPV and PEDOT-PSS layer thickness of 10 nm (1:1 ratio), respectively. The results from this work will assist the improvement of TOLED device to be implemented widely in low power and transparent electronic appliances.

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Visible Light-Assisted Charge Extraction in High-Band-Gap SrTiO3 through the Integration of a Triplet Sensitizer-Emitter Thin Film

2024-01-22 , Jie K.V.Y. , Mohd Fairus Ahmad , Mohmad A.R. , Ismail A.M. , Mohd Natashah Norizan , Ramli M.M. , Safizan Shaari , Sulaiman Y. , Shamsul Amir Abdul Rais , Shazlina Johari

A challenge in PV designs, including those with an electron transport layer (ETL), is the presence of ‘parasitic absorbers’. These are layers that absorb light without significantly converting it to electrical current, impacting the total external quantum efficiency (EQE). Strontium titanate (STO), a high-band-gap (3.20 eV) perovskite metal oxide, holds promise as an electron transport layer (ETL) for solar energy harvesting. Despite STO’s potential, it primarily operates in the UV spectrum, not fully utilizing the broader light range, and hence can be the source of parasitic absorbers. In this study, we report a significant enhancement in the EQE of STO through the integration of a triplet sensitizer-emitter (TSE) system, designed to upconvert the visible spectrum into UV light and improve the charge extraction from STO. The TSE system uses carbazolyl dicyanobenzene (4CzIPN) as a sensitizer and p-terphenyl (TP) as an emitter. To investigate the EQE of such a system, we fabricate STO as a PV cell. The revised PV cell architecture (ITO/TiO2/STO/TSE/PEDOT:PSS/Al) is a modification of the conventional configurations (ITO/TiO2/STO/PEDOT:PSS/Al). With the TSE thin film, the modified STO PV cell shows better charge extraction under sunlight compared to the standard STO PV cell, indicating that the upconversion process can enhance the hole conductions from STO to PEDOT:PSS through the TSE system. We noted an EQE increase with intense light of λ > 345 nm in thicker TSE layers and a decrease in the EQE under similar light intensity in thinner TSE layers. The Kelvin probe force measurement (KPFM) data showed that the TSE layer receives holes from STO under illumination. Additionally, time-resolved photoluminescence (TRPL) experiments showed that the TSE/STO thin film is able to produce UV emission after irradiation with lower energy light. Then, the EQE variation in thicker TSE layers under intense irradiation can be attributed to the solid-state upconversion, indicating its thickness-dependent performance. These findings underline the strategies for maximizing the utilization of the solar spectrum in PV applications.

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Low-cost tilt monitoring system for spin coater calibration

2024-02-08 , King C.Y. , Mohd Fairus Ahmad , Norhayati Sabani , Mohd Natashah Norizan , Nor Farhani Zakaria , Nurjuliana Juhari , Shamsul Amir Abdul Rais , Amin M.R.R.M.

The spin coating process became the most widely used technique in the fabrication industry for thin film coating on a substrate by centrifugal force. Unfortunately, frequent usage of spin coater might induce a tilted surface of the chuck (i.e. the sample holder). A tilted chuck might induce inhomogeneity of the coating layer. Among the machine's calibration techniques, nullifying the tilt before the spin coating process is the most important step. However, to our knowledge, none of the spin coaters was introduced with the chuck's tilt monitoring during the spin coating process. Thus, investigating the discrete condition during the spin coating process is necessary. In this work, the tilt monitoring system for the spin coater was implemented based on an Arduino Uno microcontroller and distance sensor. A spin coater has been implemented to test the tilt surface monitoring during spinning ranges from 350rpm to 1000rpm. The measurement was done under two conditions: flat (0.00 degrees) and tilted (5.71 degrees). The setup was able to measure up to 0.01 degrees of the tilt.

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Modified CMFB circuit with enhanced accuracy for data converter application

2013 , Mohd Fairus Ahmad , Sohiful Anuar Zainol Murad , Mukhzeer Mohamad Shahimin , Shamsul Amir Abdul Rais , Ahmad Fariz Hasan

Enhanced feedback voltage of common mode feedback (CMFB) circuit is designed in this work for CMOS data sampling application using 0.18-μm Silterra process technology. The double error detecting point circuit is employed to associate with the feedback point in order to prevent the undesired voltage common mode at the output of operational transconductance amplifier (OTA). The PMOS input transistor for injecting the common mode voltage is used to fit in the limitation of voltage division in low power design. The feedback voltage is strongly pushed to have a stable value as to make the outputs of differential amplifier circuit swing at a nearly constant voltage at 1.2 V for enhancing accuracy of data converter.

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A Study on Electrical Performance of SiC-based Self-switching Diode (SSD) as a High Voltage High Power Device

2023-12-01 , Sha’ari N.Z.A.A. , Nor Farhani Zakaria , Shahrir Rizal Kasjoo , Ahmad M.F. , Mohd Natashah Norizan , Ili Salwani Mohamad , Mohd Fairus Ahmad , Shamsul Amir Abdul Rais , Banu Poobalan , Norhayati Sabani

The Self-switching Diodes (SSDs) have been primarily researched and used in low-power device applications for RF detection and harvesting applications. In this paper, we explore the potential of SSDs in high-voltage applications with the usage of Silicon Carbide (SiC) as substrate materials which offers improved efficiency and reduced energy consumption. Optimization in terms of the variation in the interface charges, metal work function, and doping concentration values has been performed by means of a 2D TCAD device simulator. The results showed that the SSD can block up to 600 V of voltage with an optimum interface charge value of 1013 cm-2, making them suitable for higher voltage applications. Furthermore, it also found that the work function of the metal contact affected the forward voltage value, impacting the current flow in the device. Variation in doping concentrations also resulted in higher breakdown voltages and significantly increased forward current, leading to an increased power rating of 27 kW. In conclusion, the usage of 4H-SiC-based SSDs shows a usable potential for high-voltage applications with optimized parameters. The results from this research can facilitate the implementation of SSD in the development of high-power semiconductor devices for various industrial applications.

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Effect of indium pre-flow on wavelength shift and crystal structure of deep green light emitting diodes

2021-01-01 , Shamsul Amir Abdul Rais , Hassan Z. , Bakar A.S.A. , Rahman M.N.A. , Yusuf Y. , Md Taib M.I. , Sulaiman A.F. , Hussin H.N. , Mohd Fairus Ahmad , Mohd Natashah Norizan , Nagai K. , Akimoto Y. , Shoji D.

To produce a deep green (530 nm–570 nm) LED, the suitable indium (In) composition in the InxGa1−xN/GaN multi-quantum well (MQW) structure is crucial because a lower indium composition will shift the wavelength of emission towards the ultraviolet region. In this paper, we clarify the effects of an indium-rich layer to suppress such blue shifting, especially after the annealing process. According to characterizations by the uses of XRD and TEM, narrowing of the MQW layer was observed by the indium capping, while without the capping, the annealing results in a slight narrowing of MQW on the nearest layer to the p-type layer. By adding an indium capping layer, the blue shift of the photoluminescence was also suppressed and a slight red shift to keep green emission was observed. Such photoluminescence properties were consistent with the tiny change of the MQW as seen in the XRD and TEM characterizations.

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Photoluminescence measurement of triplet sensitizer-emitter solution using a customized 3D-printed sample holder

2024-06 , Kelvin Voon Yan Jie , Safizan Shaari , Mohd Fairus Ahmad , Nor Farhani Zakaria , Norhayati Sabani

This study explores the photoluminescence (PL) measurement of triplet sensitizer-emitter (TSE) solutions using a custom 3D-printed sample holder, within the context of triplet-triplet annihilation based molecular photon upconversion (TTA-UC) systems targeting the Vis-to-UV spectral region. TTA-UC converts low-energy visible photons to higher-energy ultraviolet (UV) photons, holding promise for solar energy harvesting and photonics applications. Two TSE couples, 4CzIPN/TP and 4CzIPN/QP, were investigated, and their upconverted fluorescence spectra showed peaks at 344 nm and 354 nm / 370 nm, respectively, confirming efficient upconversion capabilities. The 3D-printed sample holder facilitated reproducible PL measurements, enabling the calculation of quantum yields (ΦUC). The 4CzIPN/TP and 4CzIPN/QP couples exhibited low quantum yields (0.028% and 0.043%, respectively), suggesting the need for improved deoxygenation methods to enhance the triplet-triplet annihilation process and overall quantum efficiency. Despite modest yields, successful UV upconverted fluorescence observation underscores the feasibility of the Vis-to-UV TTA-UC system. This study provides insights into TTA-UC optimization and demonstrates the utility of the 3D-printed sample holder for affordable and precise PL measurements, paving the way for future advancements in photonics and solar energy applications.

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