In this study, we investigated the potential of multilayer TCO structures, specifically those mad... more In this study, we investigated the potential of multilayer TCO structures, specifically those made up of Indium Tin Oxide (ITO) and Indium Zinc Oxide (IZO), for crystalline silicon heterojunction solar cells (SHJ). We used the radiofrequency (RF) magnetron sputtering method to deposit various thin-film structures under various deposition temperatures and evaluated their electrical, optical, and morphological properties. The objective was to obtain films with lower sheet resistances and higher transmittances than those of single-layer thin films. Our results show that the ITO/IZO/ITO/IZO/ITO multilayer film structure deposited at 200 °C achieves the best sheet resistance of 18.5 Ohm/sq and a high optical transmittance of over 90% at a 550 nm wavelength. This indicates that multilayer TCO structures have the potential to be more optically and electrically efficient, and that they can improve the performance of optoelectronic devices. Finally, a power conversion efficiency of 17.46% wa...
Uluslararası mühendislik araştırma ve geliştirme dergisi, Jan 31, 2023
Öz Yüksek verimli perovskit güneş hücresi elde etmek için iğne deliği içermeyen, ince, yüksek şef... more Öz Yüksek verimli perovskit güneş hücresi elde etmek için iğne deliği içermeyen, ince, yüksek şeffaflıkta, mükemmel taşıyıcı ayırma kabiliyetine sahip, üretimi kolay elektron transfer tabakasına (ETL) sahip olması gereklidir. ETL malzemesi olarak hem kompakt (c-TiO2) hem de mezo (mp-TiO2) yapılı olarak kullanılabilen TiO2'dir. Bu çalışmada üretilen ETL, c-TiO2'in sol-jel yöntemiyle hazırlanmıştır ve farklı dönme hızlarında dönel kaplama yöntemi kullanılarak kaplanmıştır. Kaplanan ince filmlerden perovskit güneş hücreleri için en ideal kalınlıkta, iğne deliği içermeyen aktif kristalli elektron transfer tabakası belirlenerek SEM, XRD ve profilometre yardımıyla karakterize edilmiştir.
The current work describes a spectroscopic method for determining the electron temperature and el... more The current work describes a spectroscopic method for determining the electron temperature and electron density in an electron beam generator using argon spectral lines based on a collisional radiative model. Neutral and first-ionized Ar lines emitted from the electron beam generator are studied experimentally. A collisional radiative code was developed to simulate the Ar (I) and Ar (II) spectral emission and to compare the results with the experimental data for electron density and temperature determination. Ar lines and excited level densities were calculated by solving rate equations using the Gauss elimination method. The argon spectrum is recorded experimentally by superposing two discharges, namely a low pressure DC glow discharge and a high current pulsed discharge. Spectral lines between 350 nm and 950 nm were recorded using an integrated signal technique on a chargecoupled device. Electron temperature is determined by the relative intensity ratio
View the article online for updates and enhancements. Content from this work may be used under th... more View the article online for updates and enhancements. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
In this study CZTSe thin film were synthesized by a two-stage process that included sequential sp... more In this study CZTSe thin film were synthesized by a two-stage process that included sequential sputter deposition of Cu and Sn layers forming a Cu/Sn structure, pre-annealing the Cu/Sn structure at 200-380°C for some of the samples, sputtering of additional Zn and Cu over the Cu/Sn structure, evaporation of a Se cap forming a Cu/Sn/ Zn/Cu/Se precursor film, and exposing the precursor film to high temperature annealing treatment at 550°C for 15 min to form the compound. The results of the characterization carried out on the compound layers revealed that the phase content, composition and microstructure of these layers changed noticeably depending on whether or not a pre-annealing step was utilized. Although XRD studies suggested presence of secondary phases, especially in the non-pre-annealed samples, the data was dominated by kesterite CZTSe phase reflections. Raman spectra of the films verified the formation of kesterite CZTSe structure and some other phases, which were determined to be SnSe 2 and possibly ZnSe. SEM micrographs showed denser structure in the pre-annealed samples.
In this study CZTS thin films were fabricated by a two-stage process that sputter deposition of m... more In this study CZTS thin films were fabricated by a two-stage process that sputter deposition of metallic Cu, Zn, and Sn on Mo coated glass substrates and annealing process at 500 °C using various short dwell times (4, 8, and 12 min) using Rapid Thermal Processing (RTP) approach. The X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and photoluminescence were employed to characterize the CZTS samples synthesized employing different sulfurization times. It was observed that all CZTS thin films showed Cu-poor and Zn-rich composition according to EDX results. XRD patterns displayed formation of kesterite CZTS and CuS secondary phases. Raman spectra of the films justified formation of kesterite CZTS phase for all CZTS thin films and formation of CTS phase, which is difficult to distinguish by XRD pattern of the films for CZTS-8 and CZTS-12 samples. SEM images of the films displayed dense, void-free, and inhomogeneous surface structure regardless of the sulfurization time. The optical band gap of the films as determined by photoluminescence was found to be about 1.36-1.37 eV.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of Materials Science: Materials in Electronics, 2020
In this study, CZTS thin films were grown by annealing of sputtered films using quaternary single... more In this study, CZTS thin films were grown by annealing of sputtered films using quaternary single target employing various annealing parameters. The effects of the post-sulfurization treatment, reaction temperature (500, 525, 550 and 575°C) and sulfurization time (60, 90, 120 and 150 s) on the properties of CZTS thin films were analyzed. The optimization of reaction temperature for 60 s dwell time was examined by annealing the precursor films with/without sulfur atmosphere. It was shown that annealing of the films under the sulfur atmosphere prevents Zn-loss in the samples for higher annealing temperatures (550 and 575°C) and hindering the formation of secondary phases such as Cu 2-x S, Cu 2 SnS 3 (CTS). The FWHM values of the sulfurized samples revealed that the sulfurization temperature of 550°C is preferable for the fabrication of CZTS samples. Further optimization was performed at 550°C for various sulfurization times. It was seen that all the samples have Cu-poor and Zn-rich composition. The XRD pattern of CZTS samples displayed formation of kesterite CZTS phase but SnS 2 phase formations were also observed for longer sulfurization time ([ 120 s). It was also observed that the sulfurization time has more significant contribution on the crystallite size of the samples with respect to sulfurization temperature. The Raman spectra of the CZTS samples confirmed the formation of kesterite structures for all the films and appearance of secondary phase for films prepared using longer sulfurization time ([ 120 s). All the samples displayed a dense and polycrystalline surface morphology, but the sulfurized sample for 120 s displayed more homogenous and prominent morphology. The room temperature PL measurements demonstrated a broad band which peaked at about 1.36-1.37 eV, which is very close to the band gap of kesterite CZTS structure. The electrical characterization of the samples showed that all the samples have p-type conductivity and the CZTS-S-550-120 sample has a more promising result considering both resistivity and carrier concentration.
Abstract This study draws on our experiences with graphene to perform a hybrid TCO structure comp... more Abstract This study draws on our experiences with graphene to perform a hybrid TCO structure composed of AZO and graphene. We first set out to enhance the electrical and optical properties of AZO to enable its use especially in the field of solar cell. Hence, in our study, we deposited various thicknesses of AZO thin films on glass substrates and transferred single layer graphene on them to realize the formation of hybrid TCO structure. Among the various AZO film thicknesses, the optimum one, 300 nm, was determined and then the graphene film was added on top of the AZO film. This hybrid structure was applied to the silicon-based heterojunction solar cell with the idea of improving the cell performance. The cell performance fabricated using AZO film and AZO + graphene structure was analyzed using solar simulator. Our findings highlight the fact that the presence of graphene improved the cell efficiency by about 7%. Our research was further extended using ITO and ITO + graphene hybrid structure as TCO for silicon-based solar cell. We discovered that graphene incorporation increased the cell efficiency by almost 12% based on our results with ITO + graphene hybrid TCO structure on a similar cell.
In this study, Mo-bilayer film, the thickness of which was reduced to approximately 270 nm with a... more In this study, Mo-bilayer film, the thickness of which was reduced to approximately 270 nm with a very low resistivity of 14 μΩ.cm, was successfully grown by DC magnetron sputter. The Mo-bilayer, whose bottom and top layers were obtained by high pressure sputter (HPS) and low pressure sputter (LPS) respectively, demonstrates good adhesivity and crystalline properties, together with high reflectance. In order to obtain Mo-bilayer with these improved properties, we first determined the optimal growth temperature and pressure parameters by checking the structural and electrical properties respectively of Mo-single layers. As a result, we achieved a deposit of Mo-bilayer thin film that can be used as a good back contact layer in solar cell applications, both in terms of material cost saving and its superior properties, even at such low thickness.
Semiconductor quantum dots (QDs) have been widely used in various optoelectronic devices. Extensi... more Semiconductor quantum dots (QDs) have been widely used in various optoelectronic devices. Extensive studies have been devoted to the application of Si QDs with the aim of realizing various optoelectronic functions based on the modified energy band structure in QDs compared with bulk crystals. Therefore, it is necessary to be able to directly probe the carrier dynamics in single Si QDs of nanoscale dimensions deposited on a SiO 2 /Si surface, where the environment is compatible with Si-based semiconductor devices. This letter reports the observation and comparison of the ultrafast electron dynamics just after the photoexcitation of isolated and clustered Si QDs on a SiO 2 /Si surface using time-resolved photoemission electron microscopy with spatial and temporal resolutions of 50 nm and 100 fs, respectively. The detailed structure of QDs was confirmed directly by scanning electron microscopy observations. The results obtained in the present study show that the carrier lifetime in isolated QDs is shorter than that in clustered QDs. This is consistent with the electron-hole interaction in nanospace, significantly modifying the carrier recombination rates.
Ömer Halisdemir Üniversitesi Mühendislik Bilimleri Dergisi, 2019
Tek kristalli silisyum (Si) alttaşlar üzerine ince a-Si tabakalardan oluşan c-silisyum heteroekle... more Tek kristalli silisyum (Si) alttaşlar üzerine ince a-Si tabakalardan oluşan c-silisyum heteroeklem teknolojisi son yıllarda fotovoltaik (FV) alanında bir çok araştırmacı ve bilim adamı tarafından çalışılan önemli bir araştırma konusudur. Silisyum heteroeklem güneş hücre teknolojisi, yüksek enerji dönüşüm verimliliği ve rekabetçi seri üretim maliyeti ile kendisini ispat etmiş ve yeni geliştirilen teknolojileri bünyesine entegre edebilme kabiliyeti ile potansiyelini ortaya koymuş bir güneş hücresi teknolojisidir Bu çalışmada, silisyum heteroeklem güneş hücrelerinin üretim aşamaları ve karakterizasyonu detaylı bir şekilde çalışılmıştır. a-Si:H incefilmlerin kalınlık, bant aralığı ve taşıyıcı yaşam süresi gibi özellikleri elipsometre, profilometre ve taşıyıcı yaşam süresi cihazı ile araştırılmış ve optimizasyonu yapılmıştır. 6 inç n-tipi c-Si alttaş üzerine büyütülen katkısız ince film tabakalı heteroeklem (heterojunction with intrinsic thin-layer, HIT) yapısı ile %19,7 verimli güneş hücresi üretilmiştir.
In this chapter, we review and discuss some of the widely used analytical and optical methods for... more In this chapter, we review and discuss some of the widely used analytical and optical methods for characterizing Si nanoclusters in various matrices. Universal diagnostic techniques such as transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), atomic force microscopy (AFM), Raman spectroscopy (RS), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) are commonly used directly or indirectly to understand various features of ...
Sustainable Material Solutions for Solar Energy Technologies, 2021
Abstract Amongst the silicon (Si)-based photovoltaics, heterojunction solar cells are the most pr... more Abstract Amongst the silicon (Si)-based photovoltaics, heterojunction solar cells are the most promising solar cells due to their low thermal coefficient, high efficiency, and compatibility with newly emerged materials, such as graphene and perovskite. Studies on Si-based solar cells with graphene have increased dramatically in recent years. Thus far, high power conversion efficiency has been achieved up to 15 % by integrating graphene into graphene/Si Schottky junction solar cells since graphene has excellent electrical and optical properties. This chapter provides an overview of the status of the implementation of graphene into Si-based solar cells and focuses on the integration of graphene to Si heterojunction solar cells as a transparent conductive oxide. The chapter is presented in two parts. The first part reviews and discusses the literature on Si heterojunction solar cells and graphene. The second part contains experimental studies divided into three sections. We discuss photovoltaic parameters and the fabrication of Si-based heterojunction solar cells and underline the advantages and problematic issues in Section I. Section II describes graphene synthesis by chemical vapor deposition, doping, and characterization in detail. The results are discussed in relation to the current literature. Section III is devoted to Si heterojunction/graphene solar cell power conversion efficiency. This chapter concludes with predicting the future direction of high efficiency and low-cost Si heterojunction/graphene solar cells.
Abstract In this study, we investigated the impact of incorporating graphene with Ga-doped ZnO (G... more Abstract In this study, we investigated the impact of incorporating graphene with Ga-doped ZnO (GZO) when employing them as a TCO layer on Si-based solar cell. GZO thin films with various thicknesses (50–450 nm) were fabricated by the sputtering method using a single target. The aim here was to determine the GZO film with the optimum thickness to incorporate it with single layer graphene as TCO. This thickness was found to be 350 nm as that was the best crystalline quality found in the XRD pattern. Further, this sample had the lowest sheet resistance and highest transmission values as confirmed by electrical (sheet resistance), and optical characterizations (transmission). Topographic (SEM and AFM), electrical (resistivity and carrier concentration) measurements were also conducted on the same sample. The graphene film grown on copper in a CVD system was then transferred on top of this sample to fabricate the hybrid TCO structure. We found that graphene integrated GZO hybrid TCO film showed higher sheet resistance due to high sheet resistance of graphene and similar optical properties thanks to high optical transmission of graphene. Employing graphene-based TCO layer in the solar cell resulted in higher open-circuit voltage, consequently improving the conversion efficiency from 10.0% to 11.2%.
Abstract In this study, Cu2ZnSnS4 (CZTS) thin films were synthesized by a two-stage process. In t... more Abstract In this study, Cu2ZnSnS4 (CZTS) thin films were synthesized by a two-stage process. In the first stage, CuSn/Zn/Cu (E-type) and CuSn/ZnS/Cu (B-type) stacked films were formed using the sputtering method. In the second stage, precursor films were annealed in sulfur atmosphere utilizing various annealing temperatures (500, 525, 550 and 575 °C) employing the Rapid Thermal Processing (RTP) method. The EDX measurements demonstrated that almost all the samples had Cu-poor and Zn-rich compositions, as targeted. The XRD patterns of all the CZTS samples were dominated by diffraction peaks of the kesterite CZTS phase. In addition to CZTS phase, Cu–S/Sn–S based secondary phases in all E-type CZTS thin films and some B-type CZTS samples annealed at lower temperatures (500 and 525 °C) were observed. The samples annealed at above 525 °C revealed purer crystal structure in terms of secondary phases and they have more promising crystallite size in both types of CZTS thin films. The Raman spectroscopy measurements confirmed the formation of kesterite CZTS phase and distinguished the formation of Cu2SnS3 (CTS) phase for some samples. The samples annealed at 550 °C presented purer structure for potential solar cell application. The SEM surface and cross-section images of all CZTS samples displayed dense and polycrystalline structures but samples annealed at 550 °C presented a larger-grained surface and cross-section structure in both types of CZTS films. PL spectra of the B-type CZTS samples exhibited a purer band structure with respect to E type CZTS samples according to their PL band values. The best solar cell performance was achieved with CZTS thin film prepared using CuSn/ZnS/Cu stack annealed at 550 °C temperature with 252 mV, 32 mA/cm2, and 3.79% parameters.
Bu çalışmada CVD sistemi kullanılarak bakır folyo üzerinde katkısız ve nitrojen katkılı grafen se... more Bu çalışmada CVD sistemi kullanılarak bakır folyo üzerinde katkısız ve nitrojen katkılı grafen sentezi ve karakterizasyonu gerçekleştirilmiştir. / In this study, the synthesis of pristine and nitrogen-doped graphene were carried out on copper foil using CVD system and then chracterized. Şekil. Bakır alttaş üzerinde sentezlenen nitrojen katkılı grafen filme ait quaternary N, pyrolic N ve pyridinic N konfigürasyonlarının oluşumu temsili olarak gösterilmiştir. / Figure. The representation of configuration of quaternary N, pyrolic N and pyridinic N of the nitrogen doped graphene film synthesized on copper substrate.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Ömer Halisdemir Üniversitesi Mühendislik Bilimleri Dergisi, 2019
standard cleaning and single-layer homogeneous graphene synthesis was performed with these method... more standard cleaning and single-layer homogeneous graphene synthesis was performed with these methods. However, few layered and non-homogenous graphene films were obtained with applying other cleaning approaches ahead of the growth.
ABSTRACT Si and Ge nanocrystals were formed in alumina matrix by ion implantation and subsequent ... more ABSTRACT Si and Ge nanocrystals were formed in alumina matrix by ion implantation and subsequent annealing. The phase separation of the Si nanocrystals was observed using X-ray photoelectron spectroscopy by monitoring Si 2p electrons. During nanocrystal formation with a high temperature annealing Si 0 signals corresponding to Si nanoclusters increases while Si 4+ signals related to a-SiO 2 disappears from the spectrum. The transition from amorphous to nanocrystalline phase for both Si and Ge nanoclusters and the compressive ...
In this study, we investigated the potential of multilayer TCO structures, specifically those mad... more In this study, we investigated the potential of multilayer TCO structures, specifically those made up of Indium Tin Oxide (ITO) and Indium Zinc Oxide (IZO), for crystalline silicon heterojunction solar cells (SHJ). We used the radiofrequency (RF) magnetron sputtering method to deposit various thin-film structures under various deposition temperatures and evaluated their electrical, optical, and morphological properties. The objective was to obtain films with lower sheet resistances and higher transmittances than those of single-layer thin films. Our results show that the ITO/IZO/ITO/IZO/ITO multilayer film structure deposited at 200 °C achieves the best sheet resistance of 18.5 Ohm/sq and a high optical transmittance of over 90% at a 550 nm wavelength. This indicates that multilayer TCO structures have the potential to be more optically and electrically efficient, and that they can improve the performance of optoelectronic devices. Finally, a power conversion efficiency of 17.46% wa...
Uluslararası mühendislik araştırma ve geliştirme dergisi, Jan 31, 2023
Öz Yüksek verimli perovskit güneş hücresi elde etmek için iğne deliği içermeyen, ince, yüksek şef... more Öz Yüksek verimli perovskit güneş hücresi elde etmek için iğne deliği içermeyen, ince, yüksek şeffaflıkta, mükemmel taşıyıcı ayırma kabiliyetine sahip, üretimi kolay elektron transfer tabakasına (ETL) sahip olması gereklidir. ETL malzemesi olarak hem kompakt (c-TiO2) hem de mezo (mp-TiO2) yapılı olarak kullanılabilen TiO2'dir. Bu çalışmada üretilen ETL, c-TiO2'in sol-jel yöntemiyle hazırlanmıştır ve farklı dönme hızlarında dönel kaplama yöntemi kullanılarak kaplanmıştır. Kaplanan ince filmlerden perovskit güneş hücreleri için en ideal kalınlıkta, iğne deliği içermeyen aktif kristalli elektron transfer tabakası belirlenerek SEM, XRD ve profilometre yardımıyla karakterize edilmiştir.
The current work describes a spectroscopic method for determining the electron temperature and el... more The current work describes a spectroscopic method for determining the electron temperature and electron density in an electron beam generator using argon spectral lines based on a collisional radiative model. Neutral and first-ionized Ar lines emitted from the electron beam generator are studied experimentally. A collisional radiative code was developed to simulate the Ar (I) and Ar (II) spectral emission and to compare the results with the experimental data for electron density and temperature determination. Ar lines and excited level densities were calculated by solving rate equations using the Gauss elimination method. The argon spectrum is recorded experimentally by superposing two discharges, namely a low pressure DC glow discharge and a high current pulsed discharge. Spectral lines between 350 nm and 950 nm were recorded using an integrated signal technique on a chargecoupled device. Electron temperature is determined by the relative intensity ratio
View the article online for updates and enhancements. Content from this work may be used under th... more View the article online for updates and enhancements. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
In this study CZTSe thin film were synthesized by a two-stage process that included sequential sp... more In this study CZTSe thin film were synthesized by a two-stage process that included sequential sputter deposition of Cu and Sn layers forming a Cu/Sn structure, pre-annealing the Cu/Sn structure at 200-380°C for some of the samples, sputtering of additional Zn and Cu over the Cu/Sn structure, evaporation of a Se cap forming a Cu/Sn/ Zn/Cu/Se precursor film, and exposing the precursor film to high temperature annealing treatment at 550°C for 15 min to form the compound. The results of the characterization carried out on the compound layers revealed that the phase content, composition and microstructure of these layers changed noticeably depending on whether or not a pre-annealing step was utilized. Although XRD studies suggested presence of secondary phases, especially in the non-pre-annealed samples, the data was dominated by kesterite CZTSe phase reflections. Raman spectra of the films verified the formation of kesterite CZTSe structure and some other phases, which were determined to be SnSe 2 and possibly ZnSe. SEM micrographs showed denser structure in the pre-annealed samples.
In this study CZTS thin films were fabricated by a two-stage process that sputter deposition of m... more In this study CZTS thin films were fabricated by a two-stage process that sputter deposition of metallic Cu, Zn, and Sn on Mo coated glass substrates and annealing process at 500 °C using various short dwell times (4, 8, and 12 min) using Rapid Thermal Processing (RTP) approach. The X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and photoluminescence were employed to characterize the CZTS samples synthesized employing different sulfurization times. It was observed that all CZTS thin films showed Cu-poor and Zn-rich composition according to EDX results. XRD patterns displayed formation of kesterite CZTS and CuS secondary phases. Raman spectra of the films justified formation of kesterite CZTS phase for all CZTS thin films and formation of CTS phase, which is difficult to distinguish by XRD pattern of the films for CZTS-8 and CZTS-12 samples. SEM images of the films displayed dense, void-free, and inhomogeneous surface structure regardless of the sulfurization time. The optical band gap of the films as determined by photoluminescence was found to be about 1.36-1.37 eV.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of Materials Science: Materials in Electronics, 2020
In this study, CZTS thin films were grown by annealing of sputtered films using quaternary single... more In this study, CZTS thin films were grown by annealing of sputtered films using quaternary single target employing various annealing parameters. The effects of the post-sulfurization treatment, reaction temperature (500, 525, 550 and 575°C) and sulfurization time (60, 90, 120 and 150 s) on the properties of CZTS thin films were analyzed. The optimization of reaction temperature for 60 s dwell time was examined by annealing the precursor films with/without sulfur atmosphere. It was shown that annealing of the films under the sulfur atmosphere prevents Zn-loss in the samples for higher annealing temperatures (550 and 575°C) and hindering the formation of secondary phases such as Cu 2-x S, Cu 2 SnS 3 (CTS). The FWHM values of the sulfurized samples revealed that the sulfurization temperature of 550°C is preferable for the fabrication of CZTS samples. Further optimization was performed at 550°C for various sulfurization times. It was seen that all the samples have Cu-poor and Zn-rich composition. The XRD pattern of CZTS samples displayed formation of kesterite CZTS phase but SnS 2 phase formations were also observed for longer sulfurization time ([ 120 s). It was also observed that the sulfurization time has more significant contribution on the crystallite size of the samples with respect to sulfurization temperature. The Raman spectra of the CZTS samples confirmed the formation of kesterite structures for all the films and appearance of secondary phase for films prepared using longer sulfurization time ([ 120 s). All the samples displayed a dense and polycrystalline surface morphology, but the sulfurized sample for 120 s displayed more homogenous and prominent morphology. The room temperature PL measurements demonstrated a broad band which peaked at about 1.36-1.37 eV, which is very close to the band gap of kesterite CZTS structure. The electrical characterization of the samples showed that all the samples have p-type conductivity and the CZTS-S-550-120 sample has a more promising result considering both resistivity and carrier concentration.
Abstract This study draws on our experiences with graphene to perform a hybrid TCO structure comp... more Abstract This study draws on our experiences with graphene to perform a hybrid TCO structure composed of AZO and graphene. We first set out to enhance the electrical and optical properties of AZO to enable its use especially in the field of solar cell. Hence, in our study, we deposited various thicknesses of AZO thin films on glass substrates and transferred single layer graphene on them to realize the formation of hybrid TCO structure. Among the various AZO film thicknesses, the optimum one, 300 nm, was determined and then the graphene film was added on top of the AZO film. This hybrid structure was applied to the silicon-based heterojunction solar cell with the idea of improving the cell performance. The cell performance fabricated using AZO film and AZO + graphene structure was analyzed using solar simulator. Our findings highlight the fact that the presence of graphene improved the cell efficiency by about 7%. Our research was further extended using ITO and ITO + graphene hybrid structure as TCO for silicon-based solar cell. We discovered that graphene incorporation increased the cell efficiency by almost 12% based on our results with ITO + graphene hybrid TCO structure on a similar cell.
In this study, Mo-bilayer film, the thickness of which was reduced to approximately 270 nm with a... more In this study, Mo-bilayer film, the thickness of which was reduced to approximately 270 nm with a very low resistivity of 14 μΩ.cm, was successfully grown by DC magnetron sputter. The Mo-bilayer, whose bottom and top layers were obtained by high pressure sputter (HPS) and low pressure sputter (LPS) respectively, demonstrates good adhesivity and crystalline properties, together with high reflectance. In order to obtain Mo-bilayer with these improved properties, we first determined the optimal growth temperature and pressure parameters by checking the structural and electrical properties respectively of Mo-single layers. As a result, we achieved a deposit of Mo-bilayer thin film that can be used as a good back contact layer in solar cell applications, both in terms of material cost saving and its superior properties, even at such low thickness.
Semiconductor quantum dots (QDs) have been widely used in various optoelectronic devices. Extensi... more Semiconductor quantum dots (QDs) have been widely used in various optoelectronic devices. Extensive studies have been devoted to the application of Si QDs with the aim of realizing various optoelectronic functions based on the modified energy band structure in QDs compared with bulk crystals. Therefore, it is necessary to be able to directly probe the carrier dynamics in single Si QDs of nanoscale dimensions deposited on a SiO 2 /Si surface, where the environment is compatible with Si-based semiconductor devices. This letter reports the observation and comparison of the ultrafast electron dynamics just after the photoexcitation of isolated and clustered Si QDs on a SiO 2 /Si surface using time-resolved photoemission electron microscopy with spatial and temporal resolutions of 50 nm and 100 fs, respectively. The detailed structure of QDs was confirmed directly by scanning electron microscopy observations. The results obtained in the present study show that the carrier lifetime in isolated QDs is shorter than that in clustered QDs. This is consistent with the electron-hole interaction in nanospace, significantly modifying the carrier recombination rates.
Ömer Halisdemir Üniversitesi Mühendislik Bilimleri Dergisi, 2019
Tek kristalli silisyum (Si) alttaşlar üzerine ince a-Si tabakalardan oluşan c-silisyum heteroekle... more Tek kristalli silisyum (Si) alttaşlar üzerine ince a-Si tabakalardan oluşan c-silisyum heteroeklem teknolojisi son yıllarda fotovoltaik (FV) alanında bir çok araştırmacı ve bilim adamı tarafından çalışılan önemli bir araştırma konusudur. Silisyum heteroeklem güneş hücre teknolojisi, yüksek enerji dönüşüm verimliliği ve rekabetçi seri üretim maliyeti ile kendisini ispat etmiş ve yeni geliştirilen teknolojileri bünyesine entegre edebilme kabiliyeti ile potansiyelini ortaya koymuş bir güneş hücresi teknolojisidir Bu çalışmada, silisyum heteroeklem güneş hücrelerinin üretim aşamaları ve karakterizasyonu detaylı bir şekilde çalışılmıştır. a-Si:H incefilmlerin kalınlık, bant aralığı ve taşıyıcı yaşam süresi gibi özellikleri elipsometre, profilometre ve taşıyıcı yaşam süresi cihazı ile araştırılmış ve optimizasyonu yapılmıştır. 6 inç n-tipi c-Si alttaş üzerine büyütülen katkısız ince film tabakalı heteroeklem (heterojunction with intrinsic thin-layer, HIT) yapısı ile %19,7 verimli güneş hücresi üretilmiştir.
In this chapter, we review and discuss some of the widely used analytical and optical methods for... more In this chapter, we review and discuss some of the widely used analytical and optical methods for characterizing Si nanoclusters in various matrices. Universal diagnostic techniques such as transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), atomic force microscopy (AFM), Raman spectroscopy (RS), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) are commonly used directly or indirectly to understand various features of ...
Sustainable Material Solutions for Solar Energy Technologies, 2021
Abstract Amongst the silicon (Si)-based photovoltaics, heterojunction solar cells are the most pr... more Abstract Amongst the silicon (Si)-based photovoltaics, heterojunction solar cells are the most promising solar cells due to their low thermal coefficient, high efficiency, and compatibility with newly emerged materials, such as graphene and perovskite. Studies on Si-based solar cells with graphene have increased dramatically in recent years. Thus far, high power conversion efficiency has been achieved up to 15 % by integrating graphene into graphene/Si Schottky junction solar cells since graphene has excellent electrical and optical properties. This chapter provides an overview of the status of the implementation of graphene into Si-based solar cells and focuses on the integration of graphene to Si heterojunction solar cells as a transparent conductive oxide. The chapter is presented in two parts. The first part reviews and discusses the literature on Si heterojunction solar cells and graphene. The second part contains experimental studies divided into three sections. We discuss photovoltaic parameters and the fabrication of Si-based heterojunction solar cells and underline the advantages and problematic issues in Section I. Section II describes graphene synthesis by chemical vapor deposition, doping, and characterization in detail. The results are discussed in relation to the current literature. Section III is devoted to Si heterojunction/graphene solar cell power conversion efficiency. This chapter concludes with predicting the future direction of high efficiency and low-cost Si heterojunction/graphene solar cells.
Abstract In this study, we investigated the impact of incorporating graphene with Ga-doped ZnO (G... more Abstract In this study, we investigated the impact of incorporating graphene with Ga-doped ZnO (GZO) when employing them as a TCO layer on Si-based solar cell. GZO thin films with various thicknesses (50–450 nm) were fabricated by the sputtering method using a single target. The aim here was to determine the GZO film with the optimum thickness to incorporate it with single layer graphene as TCO. This thickness was found to be 350 nm as that was the best crystalline quality found in the XRD pattern. Further, this sample had the lowest sheet resistance and highest transmission values as confirmed by electrical (sheet resistance), and optical characterizations (transmission). Topographic (SEM and AFM), electrical (resistivity and carrier concentration) measurements were also conducted on the same sample. The graphene film grown on copper in a CVD system was then transferred on top of this sample to fabricate the hybrid TCO structure. We found that graphene integrated GZO hybrid TCO film showed higher sheet resistance due to high sheet resistance of graphene and similar optical properties thanks to high optical transmission of graphene. Employing graphene-based TCO layer in the solar cell resulted in higher open-circuit voltage, consequently improving the conversion efficiency from 10.0% to 11.2%.
Abstract In this study, Cu2ZnSnS4 (CZTS) thin films were synthesized by a two-stage process. In t... more Abstract In this study, Cu2ZnSnS4 (CZTS) thin films were synthesized by a two-stage process. In the first stage, CuSn/Zn/Cu (E-type) and CuSn/ZnS/Cu (B-type) stacked films were formed using the sputtering method. In the second stage, precursor films were annealed in sulfur atmosphere utilizing various annealing temperatures (500, 525, 550 and 575 °C) employing the Rapid Thermal Processing (RTP) method. The EDX measurements demonstrated that almost all the samples had Cu-poor and Zn-rich compositions, as targeted. The XRD patterns of all the CZTS samples were dominated by diffraction peaks of the kesterite CZTS phase. In addition to CZTS phase, Cu–S/Sn–S based secondary phases in all E-type CZTS thin films and some B-type CZTS samples annealed at lower temperatures (500 and 525 °C) were observed. The samples annealed at above 525 °C revealed purer crystal structure in terms of secondary phases and they have more promising crystallite size in both types of CZTS thin films. The Raman spectroscopy measurements confirmed the formation of kesterite CZTS phase and distinguished the formation of Cu2SnS3 (CTS) phase for some samples. The samples annealed at 550 °C presented purer structure for potential solar cell application. The SEM surface and cross-section images of all CZTS samples displayed dense and polycrystalline structures but samples annealed at 550 °C presented a larger-grained surface and cross-section structure in both types of CZTS films. PL spectra of the B-type CZTS samples exhibited a purer band structure with respect to E type CZTS samples according to their PL band values. The best solar cell performance was achieved with CZTS thin film prepared using CuSn/ZnS/Cu stack annealed at 550 °C temperature with 252 mV, 32 mA/cm2, and 3.79% parameters.
Bu çalışmada CVD sistemi kullanılarak bakır folyo üzerinde katkısız ve nitrojen katkılı grafen se... more Bu çalışmada CVD sistemi kullanılarak bakır folyo üzerinde katkısız ve nitrojen katkılı grafen sentezi ve karakterizasyonu gerçekleştirilmiştir. / In this study, the synthesis of pristine and nitrogen-doped graphene were carried out on copper foil using CVD system and then chracterized. Şekil. Bakır alttaş üzerinde sentezlenen nitrojen katkılı grafen filme ait quaternary N, pyrolic N ve pyridinic N konfigürasyonlarının oluşumu temsili olarak gösterilmiştir. / Figure. The representation of configuration of quaternary N, pyrolic N and pyridinic N of the nitrogen doped graphene film synthesized on copper substrate.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Ömer Halisdemir Üniversitesi Mühendislik Bilimleri Dergisi, 2019
standard cleaning and single-layer homogeneous graphene synthesis was performed with these method... more standard cleaning and single-layer homogeneous graphene synthesis was performed with these methods. However, few layered and non-homogenous graphene films were obtained with applying other cleaning approaches ahead of the growth.
ABSTRACT Si and Ge nanocrystals were formed in alumina matrix by ion implantation and subsequent ... more ABSTRACT Si and Ge nanocrystals were formed in alumina matrix by ion implantation and subsequent annealing. The phase separation of the Si nanocrystals was observed using X-ray photoelectron spectroscopy by monitoring Si 2p electrons. During nanocrystal formation with a high temperature annealing Si 0 signals corresponding to Si nanoclusters increases while Si 4+ signals related to a-SiO 2 disappears from the spectrum. The transition from amorphous to nanocrystalline phase for both Si and Ge nanoclusters and the compressive ...
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Papers by Ayse Seyhan