Browsing by Author "Dr. Saif Ur Rehman"

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A Study on Downconversion Emission: a Possible Route to Enhance Solar Cell Efficiency
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2022) Muhammad Tahir Iqbal; SP20-RPH-002; Dr. Saif Ur Rehman; LHR TP 7678
In this work, the europium doped Zinc tellurite glass was prepared by using the melting quenching method. Raman spectroscopy observe the vibrational modes, three main characteristic Raman peaks at 432 cm-1, 667 cm-1 and 744 cm-1 observed in all the samples. PL spectroscopy defines the emission behavior of the material, maximum photoluminescence intensity was observed in the hypertensive transition 5D0 - 7F2, indicating that the strong chemical interaction between the Eu3+ ion in T2, and T3 sample. The performance of the p3ht-pcbm61 solar cell improves from 1.75% to 1.84 percent (approximately 6%), and to 1.78% when covered solar cell with Eu3+doped tellurite glass and Eu3+doped tellurite glass containing gold nanoparticles, respectively. Whereas, UV-Vis spectroscopy defines absorption behaviour of the material, calculated the band gap of prepared glass sample are 3.1eV, 2.3eV, and 2.7eV for T1, T2, and T3, respectively.
Doping effect of MoS2 with Mesoporous Titanium Dioxide Nanoparticles for Efficient Dye Sensitized Solar Cell
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2020) Sania Irshad; CIIT/FA18-RPH-046/LHR; Dr. Saif Ur Rehman; LHR TP 6097
The Dye sensitized solar cell has been proved as the most propitious applicant for photovoltaic applications due to its unique premises for commercial purposes. The conversion of incident photon energy of solar radiation into electrical energy has several challenges to compete to make Dye sensitized solar cell a pragmatic solution to our energy crisis. This dissertation is dedicated to the facile approach of fabricating a low cost and efficient Dye-Sensitized Solar Cell (DSSC). The main objective was the preparation of photoanode which has been done by doping of Molybdenum disulfide (MoS2) in titania (TiO2) by using different molar ratios of nanoparticles of MoS2with TiO2in order to tune the optical properties and efficiency of DSSCs. The counter electrode was prepared by using graphite and N719 dye was used as an absorber of sunlight. As a transporter of electron triiodide electrolyte was used. Nanoparticles of TiO2has been prepared by sol-gel method and MoS2 powder has been purchased from Alfa-Aesar. After preparing nanoparticles, thin films of 0.1% MoS2 doped TiO2on FTO were deposited by doctor blade method in order to fabricate the photoanodes that were further characterized by using different analytical measuring techniques like UV-Visible spectroscopy, Scanning Electron Microscope (SEM) and Electrochemical impedance spectroscopy (EIS). At last the sandwich like structure with working and counter electrodes, DSSC was prepared and IV-measurements was performed to check the cell efficiency. Results show that for providing efficient transport pathway of charges with optimum concentration of MoS2 which is 0.1% in TiO2 provided a good electrode configuration for DSSC and enhanced efficiency from 2.21% of undoped TiO2 to 2.7% of doped TiO2 with 0.1% MoS2that enhanced the transportation of charges.
Estimation of Photovoltaic Performance of Dye Sensitized Solar Cell Using Self-Assembled Natural Dyes
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Sohaib Hassan; SP20-RPH-014; Dr. Saif Ur Rehman; LHR TP 7685
In the present work, there are four main objectives to complete such as synthesis of Zinc oxide (𝑍𝑛𝑂) nanoparticles, preparation of natural dyes, characterization of materials, fabrication of device, the Dye-Sensitized Solar Cell (DSSC) and its photovoltaic performance by the solar simulator. In this research, the sol-gel method is used for the synthesis of zinc oxide nanoparticles. The thin films of prepared 𝑍𝑛𝑂 material is deposited on FTO glass. The self assembled natural dyes are extracted from beetroot and pomegranate. Natural dyes are used rather than chemical-based dyes because of their low cost, great binding with the thin film of semiconductors, different absorption ranges, etc. Various characterization techniques are being used to analyze the prepared samples such as SEM, UV-Visible spectroscopy, FTIR, Raman spectroscopy and Solar simulation to study the surface morphology, optical properties and bonding of the samples. Scanning electron microscope (SEM) analyses showed the average particles size of around 200 nm and larger. From energy dispersive x-ray spectroscopy (EDX) analysis the elemental composition of sample is also found. The percentage composition of Zn and O were 80.15 and 19.85 observed. Raman spectroscopy analysis presented the intensity, band position and different modes of vibration. FTIR is an effective characterization technique to confirm the absorption of surfactant molecule at the ZnO surface. The UV-visible spectroscopy analysis showed the absorption spectra of self-assembled natural dyes (pomegranate) at wavelength 526.13 nm and the absorption peak is of 1.138 while for beetroot dye there were two peaks found at wavelengths 481.2 nm & 527.5nm having absorbance 1.02 & 1.03 respectively. The band gap of 𝑍𝑛𝑂 nanoparticles was found to be 3.20 eV. The working electrode was fabricated that based on the thin film of 𝑍𝑛𝑂 nanoparticles and natural dyes (pomegranate and beetroot). Solar simulation was performed to estimate the device performance, having light energy 1000 𝑚𝑊/𝑐𝑚2, to measure the photovoltaic parameters of DSSC such as the short circuit current density (𝐽𝑠𝑐), open-circuit voltage (𝑉𝑜𝑐), fill factor (𝐹𝐹) and efficiency (η). The efficiency of pomegranate and beetroot natural dyes with ZnO based DSSC was 1.0823%, and 0.81489%. It is determined that the efficiency in case of pomegranate-based dye-sensitized solar cell has greater efficiency values than beetroot dye. This result showed that natural dyes are more suitable rather than use of commercial based dyes for the construction of dye-sensitized solar cell.
Optoelectronic and Electrochemical Properties of Quantum Confined MoSe2 Grafted Graphene Nano Sheets For Energy Applications
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2022) Muhammad Faizan Hassan; CIIT/SP21-RPH-013/LHR; Dr. Saif Ur Rehman; LHR TP 8159
Next generation energy devices (batteries, super capacitors, solar cells, and LEDs) call for designing new and novel materials. Molybdenum Diselenide (MoSe2) has superior optoelectronic features among transition metal chalcogenides with high electrical conductivity and tunable size and band gap. The MoSe2/ graphene hybrids have been widely studied for Super capacitors, batteries applications but quantum confined MoSe2 Nano crystals embedded in graphene matrix have not been investigated for thin films solar cells, LEDs, and Super capacitor/batteries applications. This work explores the optoelectronic and electrochemical properties of quantum confined MoSe2 grafted graphene nanosheets for energy applications. The MoSe2 and graphene oxide were synthesized using hydrothermal and improved Hummer’s method, respectively. The CTAB concentration was varied (0.03g, 0.06g, 0.09g, 0.12g) during the hydrothermal process to control the particle size and tune the band gap of the material. The results of the Raman and photoluminescence spectroscopy, UV-Vis. spectroscopy, and CV voltammograms showed that the particle size and band gap energy can be controlled by changing the CTAB concentration. The sample with 0.06g CTAB showed the highest energy density, power density, and specific capacitance, exhibiting a battery-like charge storage mechanism and significant redox activity. The Raman Analysis of MoSe2 samples showed that by varying CTAB concentrations revealed the presence of various vibrational modes. The peaks in the spectra can be attributed to the in-plane vibration of E1g and B12g modes, as well as the J1 and J2 modes. The formation of 1T-MoSe2 and 2H-MoSe2 phases were observed in the samples, with MoSe2-(0.12g CTAB) showing dominant peaks of the 2H phase. The peaks above 450cm-1 were due to the formation of α-MoO3. The photoluminescence spectroscopy (PL) of MoSe2-GO and CTAB samples showed visible luminescence range in all samples. The PL intensity was found to be related to the recombination mechanism of photo-generated electron-hole pairs. MoSe2-GO (0.12g CTAB) showed high recombination which could be due to the CTAB capping agent covering the defect states, leading to non-radiative recombination and PL quenching. MoSe2-GO (0.06g CTAB) showed the lowest PL intensity, likely due to the highest charge separation efficiency. UV-Vis spectroscopy showed that the band gap of MoSe2 increased x with increasing CTAB concentration, indicating quantum confinement in MoSe2 Nano sheets. The estimated band gaps were 1.66eV, 2.02eV, 2.37eV, and 2.64eV in MoSe2 (0.03g CTAB), MoSe2 (0.06g CTAB), MoSe2 (0.09g CTAB), MoSe2 (0.12g CTAB) respectively. The absorption spectra of MoSe2-GO composites showed a characteristic absorption peak of GO at 261nm, 274nm, 276nm, and 275.8nm and a broad absorption region assigned to MoSe2 nanosheets decorated on the GO network. The CV voltammograms of different samples were recorded at various scan rates and showed an increase in current density with an increase in scan rate. The sample with intermediate concentration of CTAB showed higher specific capacitance values. The sample with 0.09g CTAB showed efficient charge separation and poor charge recombination mechanism. The sample with 0.06g CTAB showed the highest energy density, power density, and specific capacitance. The samples exhibited battery-like charge storage mechanism and significant redox activity. The GCD curves of the samples exposed a triangular shape attributed to super capacitors. The study concludes that the CTAB hydrothermal process is very effective in controlling the properties of MoSe2/graphene nanosheets and holds a great potential for energy storage and conversion applications.
Photovoltaic Properties of Dye Sensitized Solar Cells Composed of Titanium Dioxide and Zinc Oxide Nanostructures
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2020) Sana Munir; CIIT/FA18-RPH-016/LHR; Dr. Saif Ur Rehman; LHR TP 6359
Dye sensitized solar cell as part of third generation photovoltaic is one of most primitive candidate of photovoltaic applications due to low cost and suitable commercial properties. In this appraisal, the thin films of bared Titania, bare zinc oxide and their different compositions are prepared by sol-gel synthesis. Different techniques are used to characterize the prepared samples. To study the optical properties of samples, UV-Visible technique was used, the UV-Vis results shows the band gap as well as the absorption. The maximum absorption found in case of nanocomposite having ratio as 75% TiO2/25% ZnO. The band gap for bare TiO2 and bare ZnO is 3.2eV and 3.5eV respectively while for other composition with 25%TiO2/75 ZnO, 50% TiO2/50% ZnO and 75% TiO2/25% ZnO the band gap values are 3.33eV, 3.12eV, 2.98eV respectively. The difference in values may attributed to change of composition, calcined temperature difference. FTIR technique used to take information about bond vibrations. The peaks in FTIR results shows that intensity increases. In case of 75% TiO2/25% ZnO than other nanocomposites. Raman analysis is used to study the different vibration modes. The peaks at 1450. The AFM is used to determine surface topography of prepared samples/thin films. The clouds/flakes were found while in case of 75% TiO2/25% ZnO thin film the clear particles have been seen. The average particle size is about 120nm. The SEM is used to study surface morphology and particle size. The ZnO nanostructures (nano-blocks shaped) are formed as result of bare zinc while in bare Titania the nanostructures are formed. The clusters are formed in all nanocomposite but for sample containing 75% Titania the clusters are monodispersed and is most suitable for photovoltaic applications.
Sol-Gel Synthesis of Copper Doped TiO2 Thin Films for Third Generation Solar Cells
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Muhammad Tariq; CIIT/SP20-RPH-026/LHR; Dr. Saif Ur Rehman; LHR TP 7690
Dye-sensitized solar cells (DSSCs) have gained a great attention because they deliver good efficiency in power conversion, ease of manufacturing and lower costs, making them the most promising alternatives to traditional photovoltaic systems. DSSC photo-anodes were manufactured using nanostructures of undoped Titanium dioxide (TiO2) and Copper (Cu) doped TiO2 (CTO) in this study (2% and 4% concentration by wt. of Cu). The sol-gel process was utilized to synthesize these nanostructures. For materials analysis, Raman Spectroscopy, FTIR, UV-Visible (UV-Vis) spectrophotometer, EDS analysis, and scanning electron microscopy (SEM) were used to evaluate the material's properties, such as structural, optical, and morphological properties of prepared nanostructures. The FTIR spectra of three samples showed that intensity varied as we change the Cu concentration with TiO2. The peak intensity decreases in case of 2% and and 4% CTO. The Raman spectra of bare TiO2 and Cu doped TiO2 showed the shift in peaks, more intense peak is observed at 606cm-1 corresponding to A1g mode in TiO2. The lower peak is at 413cm-1 in case of 2% while in 4% CTO it is shifted to 404cm-1. SEM analysis revealed that doping of Cu with TiO2 increase the surface area of TiO2 nanoparticles and hence increase the conversion efficiency of cells. The average particle size of doped titania was observed about 60 nm. EDS analysis of the samples is done along with the SEM analysis to study the elemental composition of the samples. The EDS analysis of the bare andCu doped titania confirmed the synthesis of titania nanostructures and Cu doping. In UV-Visible analysis, the absorption improves with increasing Cu doping concentration, whereas the band gap decreases from 3.25 eV to 3.02 eV. The band gap value of undoped TiO2 is measured to be 3.25 eV, which was calculated using tauc plot. The band gap of 2% CTO was 3.17 eV, and of 4% CTO was measured as 3.02 eV. The solar cell device was fabricated, and solar simulations (J-V measurements) were performed, the photovoltaic parameters such as open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and efficiency (𝜂) were calculated. Simultaneous improvements in photovoltaic performance were achieved by Cu doping. In comparison with bare titania and 2% CTO, the 4% Cu doped TiO2 exhibits the higher efficiency (𝜂) of 1.76%.
Study of Doped Sb2S3 Sensitizer for Third Generation Solar Cell
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2019) Muhammad Saqib; CIIT/FA17-RPH-013/LHR; Dr. Saif Ur Rehman; LHR TP 5714
The dye-sensitized solar cell has been investigated as the most promising candidate for photovoltaic applications due to its unique properties, low cost and suitable power conversion for commercial purposes. In this dissertation the thin films of Sb2S3 are synthesized by hydrothermal method with different doping ratios of copper (Cu). The prepared material is further characterized by different techniques. UV-Vis is used to analyze the absorption spectrum of both doped and un-doped materials. The results show that the absorption spectrum have sharp edge close to the band edge which indicates that it has direct band gap. The band gap calculations are 2.01 eV in case of un-doped Sb2S3 and 1.32 eV to 1.45 eV in case of 3% - 5% Cu doping. This variation in band gap calculations can be attributed to change in film thickness and higher concentrations of Cu doping. FTIR is used to analyze the bond vibrations of different groups which are present in Sb2S3 with different Cu-doping ratios. The peaks in FTIR spectra indicate that the peak intensity is increased with 3% cu-doping but decreased with 5% Cu-doping. Raman spectroscopy is used to analyze the different frequency modes present in the material. The peaks at approximately 260cm -1 and 950cm -1 are representing the different symmetric and anti- symmetric Sb-S stretching present in the material. The SEM results show the spherical shapes of un-doped Sb2S3 nanoparticles having average size range 80 nm but in case of 3% Cu doping, the nanoparticles make clusters or bunches with each other which indicate that by doping with different Cu ratios, the structure have been changed. It has been observed that with 5% Cu and above the doping will agglomerate the material which is not feasible for solar cell applications. The maximum energy conversion efficiency is recorded 1.4% with 3% Cu doping having FF of 0.75, Voc of 0.70 V and Jsc of 27 mAcm -2 . The efficiencies of un-doped and 5% are recorded as 0.76% and 0.96% with different values of Jsc, Voc and FF. This variation of efficiency can be related to different grain size and chemical composition of material
Study of Optical, Morphological and Structural Properties of Mg Doped ZnO Nanoparticles Prepared by Coprecipitation Method
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) MUHAMMAD AWAIS ALI; CIIT/SP20-RPH-049/LHR; Dr. Saif Ur Rehman; LHR TP 7697
Zinc oxides (ZnO) are commonly employed as semiconductor variables in solar fusion due to their large bandgap. This dissertation includes the preparation of undoped ZnO and Mg doped ZnO (MZO) nanoparticles using coprecipitation method. Different concentration of Mg (2%, 4%) wt. ratios were used to dope with bare ZnO. Structural, morphological, and optical properties were studied using Raman spectroscopy, Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and UV-Vis spectroscopy. Raman spectroscopy was used to detect the electron-phonon interaction in ZnO. The FTIR spectra revealed several peaks, each of which corresponded to a different functional group. The field emission scanning electron microscopy used to study the surface morphology and particle size of the prepared nanostructures. The average size of the undoped ZnO nanoparticle was 110 nm, while the 2% MZO and 4% MZO the sizes are 125 nm and 150 nm respectively. Increasing of Mg concentration resulted in increased particle size. UV- Visible spectroscopy was utilized to assess the absorbance and bandgap of doped and Mg doped ZnO nanoparticles. In case of 4% MZO doping the higher absorption (5.66) found with band gap of 3.320 eV. Raman analysis verified phase segregation due to the significant E2 mode. It is a promising option for optoelectronics, spintronics, and solar cells since it can be doped to close the band gap. “
Study of Thermoelectric and Optical Characteristics of Zn Doped Cu2O Thin Films
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2022) ALI AHSAN; CIIT/FA20-RPH-003/LHR; Dr. Saif Ur Rehman
Cuprous Oxide (Cu2O) based semiconductor materials have lately attracted attention for their electrical and optical properties owing to its potential usage in cutting-edge electronics and solar cells. The current research is focused on thermoelectric and optical properties of Zinc (Zn) doped Cu2O. Thin films of pure and Zn doped Cu2O were deposited by spin coating technique and optical properties were examined via ellipsometry. To cross check the parameters, the simulation studies were also done. The density functional theory calculations were used to model Zinc (Zn) incorporated Cu2O crystals and predict their thermoelectric and optical responses. All the simulations were performed using an extended gradient approximation method, with the full-potential linearized augmented plane wave technique taken into account. Solutions were prepared by Sol gel route and then Spin coating technique was used to create Cu2O thin films with a consistent morphology that were either pure or included Zn at concentrations of 3.125, 6.25, and 12.5 wt.%. There is a strong relationship found between electrical, optical, and thermoelectric characteristics, by both ab-initio and experimental studies. The experimental results were in well agreement with simulation results. With the addition of Zn to the Cu2O structure, a reduction in the band gap was observed and an optical band gap of 1.9eV was recorded for 12.5 wt.% Zn doped Cu2O but in undoped Cu2O a higher optical band gap of 2.2eV was observed. In the visible range, the absorption coefficient and real epsilon show a dramatic increase with Zn doping. Doped samples also showed higher values of Seebeck coefficient for a wide temperature range as compared to the undoped samples. Due to their unique properties, the results suggest that these materials might be used in a variety of optoelectronic and dielectric devices.
Synthesis and Characterization of Al Doped ZnO Nanorods by Hydrothermal Method for DSSC Applications
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) MUHAMMAD USMAN AFZAL; CIIT/SP19-RPH-027/LHR; Dr. Saif Ur Rehman; LHR TP 7243
In the forthcoming times solar energy is viewed as a key participant among all environmentally friendly energy sources. As the sun is providing energy continuously, the scientific community is looking for cost effective, environmentally friendly and highly efficient methods distribute and store solar energy. In this thesis, ZnO nanorods (NRs) and Al doped ZnO (AZO) NRs (different concentration of Al) are synthesized using hydrothermal method. Photo electrodes are fabricated using undoped ZnO NRs, 2% and 4% Al dopped ZnO NRs using hydrothermal method on seed layer precoated with ZnO using dip-coating method for undoped ZnO NRs 2% and 4 % Al-doped ZnO NRs on FTO glass substrate. Prepared samples were characterized using different techniques such as Field Emission Scanning Electron Microscope (FE-SEM) and UV-Vis spectroscopy. SEM analysis showed increase in diameter and length along with increase in spacing between ZnO NRs due to Al doping. The diameter of the NRs vairy from 20 nm to 250 nm and their lengths were increased from 300 nm to 2 micron was observed. For undoped ZnO NRs the average diameter is approximately 30 nm and average length was 300 nm. For 2% Al-doped ZnO NRs the approximate diameter is 100 nm with average length of NRs is of 1 micron and for 4% Al-doped ZnO NRs the diameter of the NRs appears to be ~250 nm having average length of 2 micron. UV-Vis reveal the absorption spectrum for Undoped, 2% Al-doped and 4% Al-doped ZnO NRs. The results reveal that the 4% Al-doped ZnO NRs show maximum absorption and minimum transmission having least bandgap of 3.03 eV calculated using Tauc plot. Moreover, photovoltaic performance was investigated using J-V curves. For undoped ZnO NRs based DSSC produce short-circuit current density (J_sc) of 2.0139 mA/cm2, open circuit voltage (V_oc) of 0.709 V, fill-factor (FF) of 0.5497 and power conversion efficiency (η) of 0.78% while for 2% AZO NRs based DSSC produce J_scof 2.6357 mA/cm2, V_oc of 0.736 V, FF of 0.5565 and efficiency of 1.07% and 4% AZO NRs based DSSC produce J_sc of 2.837 mA/cm2, V_ocof 0.723 V, FF of 0.574 and efficiency of 1.17%. Results indicate that power conversion efficiency is maximum for 4% Al-doped ZnO NRs due to larger spacing between prepared NRs. J-V curve show max efficiency of 1.17% for 4% Al-doped ZnO.