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Öğe An Investigation on CdSeTe/CdTe Stacks Deposited by Evaporation: Impact of Halide Treatment Depending on the Applied Surface(Wiley-V C H Verlag Gmbh, 2024) Ciris, Ali; Atasoy, Yavuz; Tomakin, Murat; Bacaksiz, EminAmong the methods applied to modify the characteristics of CdSeTe/CdTe stacks, one of the most well-known and widely used procedures is the CdCl2 halide treatment. In this connection, the influence of CdCl2 on microstructural properties, phase distribution, and optical properties of CdSeTe/CdTe stack depending on location of the employed surface is investigated. In CdSeTe/CdTe stacks deposited by evaporation in vacuum, CdCl2 halide treatment is applied to the interface of CdSeTe and CdTe, the upper surface of CdTe, and both surface regions of the stack. CdCl2 treatment applied depending on the region has a definite effect on the phase structure, interlayer CdSexTe1-x alloying rate, and crystallization quality of the stack structure. Regardless of the applied region, all CdCl2-treated stacks exhibit a granular and compact surface morphology. On the other hand, CdCl2 treated only on single surface results in a shift of the absorption edge to the shorter wavelength, but rather to the long spectral region for both surfaces. The photoluminescence spectra reveal the presence of band emissions of the CdTe layer and CdSeTe alloys. Overall, the findings of the study indicate that only the upper-surface application of CdCl2 has more promising features for potential solar cell applications.Öğe Characterization of Cu(In,Ga)(Te,S)2 thin films grown on stainless steel foil substrates(Iop Publishing Ltd, 2023) Karaca, Abdullah; Basol, Bulent M.; Olgar, M. Ali; Buyuklimanli, Temel; Tomakin, Murat; Kucukomeroglu, Tayfur; Bacaksiz, EminIn this study, Cu(In,Ga)(Te,S)(2) (CIGTS) thin films with [Ga]/([In] +/- [Ga]) atomic ratios in the ranges of 0.22-0.28 and 0.50-0.67 were fabricated using a two-stage technique. During the first stage of the technique, in one set of samples, Cu, In and Ga layers were deposited by electrodeposition on a Mo coated stainless steel (SS) foil substrate forming a SS/Mo/Cu/In/Ga precursor structure. For another set of samples, a Te layer was also deposited by e-beam evaporation on the SS/Mo/Cu/In/Ga structure forming a SS/Mo/Cu/In/Ga/Te precursor structure. During the second stage, SS/Mo/Cu/In/Ga and SS/Mo/Cu/In/Ga/Te stacks were reacted using rapid thermal annealing (RTA) for 5 min at 600 degrees C with or without presence of S vapors to produce CIGTS series thin films. SS/Mo/Cu/In/Ga stack under S atmosphere yielded CuInGaS2 with a Ga-In gradient across the thickness by RTA process. SS/Mo/Cu/In/Ga/Te stack reacted without S in the reaction atmosphere yielded the CuInGaTe2 compound. When S was present, the same stack with top Te layer yielded only CuInGaS2 compound. When, however, already formed CuInGaTe2 compound layers were heated in S environment at 400 degrees C, some Te could be retained in the films in the form of elemental Te. Gallium and In grading in various reacted films were evaluated by x-ray diffraction, secondary-ion mass spectrometry and EDS. CIGTS films showed highly (112) preferred oriented chalcopyrite phase and with the increase of Ga content, shifts were observed in the XRD peak positions demonstrating Ga inclusion in the lattice. Gibbs free energy calculations were used to explain the preferred reaction of S with metallic constituents when both S and Te were present for reaction.Öğe Comparison of the impact of different chlorination treatments to ZnS and CdS thin films(Academic Press Ltd- Elsevier Science Ltd, 2022) Ciris, Ali; Atasoy, Yavuz; Tomakin, Murat; Bacaksiz, EminIn this study, the effect of ZnCl2 and CdCl2 treatments on the structural, optical and electrical properties of ZnS and CdS thin films grown by chemical bath deposition method was examined. Employing CdCl2 or ZnCl2 treatment to CdS caused a change from cubic to hexagonal structure. After treating ZnS with CdCl2, ZnS phase disappeared and a highly crystalline hexagonal CdS phase formed. CdCl2 treatment on CdS showed an improving effect on surface morphology, but ZnCl2 led to an unfavorable effect. CdCl2 treatment to ZnS was transformed it into a fused structure in which individual grains were disappeared. Treatment of ZnCl2 to ZnS and CdCl2 to CdS induced a slight increase in the amount of Zn and Cd, respectively. However, processing of CdCl2 to ZnS (or ZnCl2 to CdS) resulted in significant quantity of Cd (or Zn) elements in the samples. The transmittance of CdS decreased with CdCl2 and ZnCl2 treatments. However, the highest transmittance in ZnS thin films was achieved after ZnCl2 treatment. According to PL spectra, different emission types increased partially in CdS/CdCl2, but decreased in CdS/ZnCl2. After applying ZnCl2 treatment to ZnS, the emission type appears similar to the as deposited sample, while CdCl2 treatment caused the emission type to change. Electrical measurements showed that the resistivity and carrier concentrations of the samples were in the order of 10(3) Omega cm and 10(13) cm(-3), respectively. The carrier concentrations of the CdS/ZnCl2 and ZnS/CdCl2 sample increased slightly compared the as deposited samples.Öğe Deposition of CdSeTe alloys using CdTe-CdSe mixed powder source material in a close-space sublimation process(Springer, 2021) Ciris, Ali; Basol, Bulent M.; Atasoy, Yavuz; Karaca, Abdullah; Kuckomeroglu, Tayfur; Tomakin, Murat; Bacaksiz, EminCdSexTe1-x films were deposited using a close-space sublimation (CSS) method and CdSe + CdTe mixed powders as the source material. Composition of the source was changed to obtain films with varying x values, and the resulting films were characterized by XRD, SEM, photoluminescence, Raman and optical transmission measurements. All data agreed with the fact that as the Se content of the source material was increased, the composition parameter x also increased. GI-XRD measurements showed the films to be graded in composition, the surface region being more Se-rich. Band gap values obtained from optical measurements showed a minimum band gap of about 1.4 eV for the material that had the highest Se content of about 45% near its top surface. Energy gap vs composition data demonstrated the expected bowing effect in band gap values and a bowing parameter of 0.678 was determined.Öğe Effect of CdS and CdSe pre-treatment on interdiffusion with CdTe in CdS/CdTe and CdSe/CdTe heterostructures(Elsevier Sci Ltd, 2021) Ciris, Ali; Basol, Bulent M.; Atasoy, Yavuz; Kucukomeroglu, Tayfur; Karaca, Abdullah; Tomakin, Murat; Bacaksiz, EminHigh efficiency CdTe solar cell structure has the configuration of CdS/CdSe/CdTe. Depending on the deposition and post deposition techniques employed, this stack is often subjected to high temperatures, often in presence of CdCl2, which leads to various degrees of interdiffusion at the CdS/CdSe and CdSe/CdTe interfaces. Such interdiffusion greatly influences device performance. Therefore, understanding and controlling these interdiffusion processes are important. In this contribution, interdiffusion between CdS-CdTe and CdSe-CdTe pairs were studied using CdS/CdTe and CdSe/CdTe stacks annealed at 673 K. Effect of pre-treating the CdS and CdSe layers with CdCl2 before the CdTe deposition on this interdiffusion was investigated. CdS films were grown by CBD and CdSe and CdTe films were vacuum evaporated. CdTe thickness was intentionally kept at the low 150?200 nm range to more easily identify alloy phases formed. GA-XRD measurements demonstrated that in absence of any CdCl2 pretreatment, there was more interdiffusion between CdSe and CdTe compared to CdS and CdTe. In all cases CdCl2 pre-treatment of CdS or CdSe before the deposition of the CdTe film was found to reduce diffusion of S and Se into CdTe.Öğe Effect of ultra-thin CdSexTe1-x interface layer on parameters of CdTe solar cells(Pergamon-Elsevier Science Ltd, 2022) Ciris, Ali; Basol, Bulent M.; Atasoy, Yavuz; Karaca, Abdullah; Tomakin, Murat; Kucukomeroglu, Tayfur; Bacaksiz, EminEffects of an ultra-thin CdSexTe1-x junction interface layer on CdTe solar cell parameters were investigated employing a CdSexTe1-x/CdTe absorber structure. CdSexTe1-x thin films with varying composition were grown by vacuum evaporation and CdTe films were produced by the close spaced sublimation (CSS) method. XRD analysis showed that while the CdSexTe1-x layers with x values less than 0.39 crystallized in cubic structure, films that were richer in Se displayed a (cubic + hexagonal) mixed phase. SEM analysis demonstrated a morphology with compact grains for all films. However, the grain size decreased appreciably with increasing Se content. Optical measurements showed that the band gaps of the alloys reached the minimum value of 1.40 eV at x similar to 0.32. CdS/CdSexTe1-x/CdTe solar cells were fabricated employing 100 nm thick CdSexTe1-x interlayers. The Grazing Incidence (GI)-XRD spectra of CdSexTe1-x used in the device structure showed that these inter-layers had graded alloy composition. The average Se-concentration within the graded alloy films were found to agree with the values obtained by EDS. Conversion efficiencies of 9.59% 11.69% and 10.13%, were obtained for x values of 0.24, 0.32 and 0.39, respectively. Spectral response showed enhanced long wavelength response for all devices due to the presence of the CdSexTe1-x interlayer. It was concluded that using an ultra-thin CdSexTe1-x inter-layer with optimum properties between CdS (junction partner) and CdTe improves the cell performance by increasing the current density of the device.Öğe Growth and characterization of CT(S,Se) thin films and Al/n-Si/p-CT(S,Se)/Mo heterojunction diode application employing a two-stage process(Elsevier Science Sa, 2023) Bayazit, Tugba; Olgar, M. Ali; Kucukomroglu, Tayfur; Bacaksiz, Emin; Tomakin, MuratCu2SnS3 (CTS), Cu2Sn(S,Se)(3) (CTSSe), and Cu2SnSe3 (CTSe) thin films were deposited on n-type silicon wafer substrates using a two-stage process. This process involved drop-coating Cu-Sn precursors, which is different from the vacuum-based fabrication methods. The sulfurization/selenization of the films was achieved using the rapid thermal processing (RTP) method at 550 degrees C. The structural, morphological, and optical properties of CTS, CTSSe, and CTSe thin films were investigated. Al/n-Si/p-CTS/Mo, Al/n-Si/p-CTSSe/Mo, and Al/n-Si/p-CTSe/Mo heterojunction diodes were formed, and electrical characterizations were performed. According to the performed analyses, it was detected that while CTS and CTSSe thin films had a Cu-poor chemical composition (Cu/Sn similar to 1.7), the CTSe thin film showed a Cu-rich chemical composition. X-ray diffraction (XRD) and Raman spectra of the samples showed that all samples had a monoclinic crystal structure as a dominant phase. Scanning electron microscope (SEM) images showed that the incorporation of selenium (Se) into prepared samples contributes to form a larger-grained structure. The band gap (E-g) of CTS, CTSSe, and CTSe thin films was determined from the optical reflectance measurements, and they were found to be 1.02 eV, 1.00 eV, and 0.96 eV, respectively. According to the data obtained from the I-V measurements of the heterojunction diode, the incorporation of Se into the film structure reduced the series resistance (R-s) in the heterojunctions from 8.27 x 10(2) Omega to 2.42 x 10(2) Omega, and the best ideality factor value was obtained in the Al/n-Si/p-CTSe/Mo heterojunction with a n = 2.87 value.Öğe Hybrid transparent conductive electrode structure for solar cell application(Pergamon-Elsevier Science Ltd, 2021) Altuntepe, Ali; Olgar, Mehmet Ali; Erkan, Serkan; Hasret, Onur; Kececi, Ahmet Emin; Kokbudak, Gamze; Tomakin, MuratThis 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. (c) 2021 Elsevier Ltd. All rights reserved.Öğe Impact of CdSeTe and CdSe film deposition parameter on the properties of CdSeTe/CdTe absorber structure for solar cell applications(Iop Publishing Ltd, 2024) Ciris, Ali; Atasoy, Yavuz; Tomakin, Murat; Karaca, Abdullah; Kucukomeroglu, Tayfur; Bacaksiz, EminIn this study, the effect of depositing CdSeTe and CdTe layers at different substrate temperatures (STs) by evaporation in vacuum on the properties of the CdSeTe/CdTe stacks was investigated. First, CdSeTe layers in stack structure were grown at STs of 150 degrees C, 200 degrees C and 250 degrees C and then CdTe layers on the CdSeTe produced with the optimum temperature were coated at STs of 150 degrees C, 200 degrees C and 250 degrees C. The employing of STs up to 150 degrees C on both CdSeTe and CdTe films in CdSeTe/CdTe stacks demonstrated the presence of Te and/or oxide phases as well as the alloying, while more stable phase structures at higher temperatures. In the CdSeTe/CdTe stack, the increase in ST of CdSeTe promoted the alloying, while it weakened the alloy in which was applied in CdTe. It was concluded that under the applied experimental conditions, STs of 250 degrees C and 200 degrees C with the graded alloying structure, suitable absorption sites, more homogeneous surface morphology for potential solar cell applications would be more suitable for CdSeTe and CdTe, respectively. As a result, the application of ST to CdSeTe or CdTe in the stacks can be used as a tool to control the properties of the stack structure.Öğe Influence of deposition pressure of elemental Sn on structural, optical, electrical and schottky diode properties of SnS thin films grown by two-stage method(Springer, 2023) Ciris, Ali; Atasoy, Yavuz; Tomakin, Murat; Olgar, Mehmet AliIn the present study, SnS thin films were grown by two-stage method including sputtering deposition of elemental Sn films at various deposition pressures (6, 9, 12 ,15 and 18 mTorr) followed by sulfurization process carried out by Rapid Thermal Processing method at 350 degrees C for 1 min. The fabricated SnS thin films were characterized by several techniques. The energy dispersive X-ray spectroscopy measurements showed that deviation from stoichiometry in chemical composition of SnS samples deposited at above 9 mTorr was observed. X-ray diffraction and Raman spectroscopy measurements confirmed formation of orthorhombic SnS phase and SnS2 secondary phase. Furthermore, both characterization method also revealed that the preferential orientation of orthorhombic SnS phase altered from (111) to (040) by increasing the deposition pressure at above 9 mTorr. Scanning electron microscope images displayed formation of polycrystalline surface morphology. While lower deposition pressure (6 mTorr) gave rise to form small grains, the high deposition pressure (above 12 mTorr) caused some agglomerations. Optical bandgap of the films varied between 1.02 eV and 1.08 eV by varying the deposition pressure. SnS samples prepared at 9 and 12 mTorr deposition pressures presented lower resistivity and higher carrier concentration values. Due to more promising results of SnS samples fabricated utilizing 9 and 12 mTorr deposition pressures regarding structural and electrical properties, Schottky diode properties of both samples were investigated. The current-voltage characteristic of Mo/SnS/Al diode structure showed that SnS samples prepared at 12 mTorr has more ideal diode characteristic, comparatively.Öğe Performance of Si-based solar cell utilizing optimized Al-doped ZnO films as TCO layer(Springer, 2023) Altuntepe, Ali; Erkan, Serkan; Hasret, Onur; Yagmyrov, Atajan; Yazici, Duygu; Tomakin, Murat; Olgar, Mehmet AliAluminum-doped zinc oxide (AZO) is one of the most popular transparent conducting oxide layers that can be employed in many optoelectronic applications in particular in photovoltaic devices due to being a low-cost and nontoxic material. In this study, we report on the effect of deposition pressure and substrate temperature on the properties of AZO films and solar cell performance by employing the optimized films. This study consists of two stages, the first of which concerns the optimization deposition pressure while the second is the substrate temperature of AZO films by evaluating the structural, optical, and electrical properties of the films. The deposited AZO thin film under 10 mTorr deposition pressure exhibited high optical transmission (89.9%), low electrical resistivity (9.1 x 10(-2) omega.cm), and high carrier concentration (3.74 x 10(19) cm(-3)) among the others. The impact of substrate temperature was then investigated using this deposition pressure at room temperature, 150, 200, and 250 ?. The deposited AZO films at 150 ? temperature were found to possess the highest optical transmission (91.1%), lowest resistivity (9.9 x 10(-4) omega.cm), and highest carrier concentration (1.1 x 10(20) cm(-3)) values. Hence, the 10 mTorr deposition pressure and 150 ? substrate temperature were selected as the optimum growth parameters to obtain AZO films, which were then employed in the cell structure. It was, thus, revealed that utilizing AZO films in silicon-based solar cell using such parameters led to the enhancement in the cell efficiency.Öğe Photodetector properties of CdSe thin films grown by close space sublimation method(Springer, 2023) Olgar, M. Ali; Basol, Bulent M.; Polat, Ismail; Tomakin, Murat; Kucukomeroglu, Tayfur; Bacaksiz, EminIn the present study, CdSe thin films were grown by Close Space Sublimation (CSS) method on glass substrates at elevated temperatures. The prepared films were analyzed through several characterization techniques such as XRD, SEM, EDX, optical transmission, and photoluminescence. Films had single phase hexagonal crystal structure without any obvious secondary phase segregation. The preferred orientation was (002). SEM images taken from the surface and cross-section of the layers showed well-defined faceted microstructure with a grain size ranging from 0.5 to 1.0 & mu;m. The chemical composition was stoichiometric. Optical band gap calculated from the optical transmission was determined to be 1.73 eV. Room temperature PL spectra showed a single strong peak located at around 715 nm that can be attributed to free carrier-to-band or band-to-band optical transitions. The performance of photodetector devices constructed using the CSS grown CdSe films showed a wavelength dependent behavior, shorter wavelength light generating higher photocurrent. It was seen also determined that the responsiveness and detectivity values increased with decreasing value of the light wavelength. Switching properties, responsivity and detectivity of the photodetectors were studied. The maximum responsivity was observed at 714 nm. Devices yielded the highest photocurrent at a wavelength of 443 nm.Öğe Processing CdS- and CdSe-containing window layers for CdTe solar cells(Iop Publishing Ltd, 2021) Ciris, Ali; Basol, Bulent M.; Atasoy, Yavuz; Karaca, Abdullah; Tomakin, Murat; Kucukomeroglu, Tayfur; Bacaksiz, EminThe influence of heat treatment steps on the characteristics of (CdS, CdSe) junction partners and on solar cell performance was studied. CdS films were obtained by chemical bath deposition, and CdSe layers were evaporated. Structural and compositional properties of CdS/CdSe bilayer stacks did not change upon heat treatment at 400 degrees C up to 10 min, whereas heat treatment in the presence of CdCl2 for 10 min caused formation of a CdSSe alloy with a bandgap value of about 2.05 eV. Originally, the cubic structure of the stack was also transformed into a hexagonal structure during this treatment. CdSe-CdTe interdiffusion was also studied using CdS/CdSe/CdTe triple layer stacks. CdTe films were deposited using a close-spaced sublimation method. Limited CdSe-CdTe interdiffusion was seen when CdTe was deposited over the as-deposited CdSe layer at 580 degrees C. However, such interdiffusion was not detected for samples where CdTe deposition was carried out on CdS/CdSe stacks pre-annealed in the presence of CdCl2. This suggests that partial crystallization of the CdS/CdSe bilayer stack by CdCl2 reduced such an interaction. Solar cells with CdSe/CdTe, CdS/CdTe and CdS/CdSe/CdTe structures with efficiencies of 8.39%, 10.12% and 11.47% were fabricated using 4.5-5 mu m thick CdTe layers and a final CdCl2 treatment. Quantum efficiency measurements demonstrated the benefit of CdSe-CdTe alloying during the final CdCl2 treatment in improving the short circuit current values.Öğe The effect of ZnCl2 and CdCl2 treatment on ZnS/CdS junction partner on CdTe cell performance(Elsevier Sci Ltd, 2022) Ciris, Ali; Atasoy, Yavuz; Karaca, Abdullah; Tomakin, Murat; Kucukomeroglu, Tayfur; Bacaksiz, EminIn this study, the impacts of ZnCl2 and CdCl2 treatments on the structural and optical properties of ZnS/CdS bilayers and on the parameters of CdTe solar cells with ZnS/CdS junction partners were investigated. CdS and ZnS thin films were grown by chemical bath deposition. In the as deposited ZnS/CdS sample, hexagonal CdS and Zn(S,O) phases were formed. After the application of CdCl2 treatment to the sample, ZnO and CdZnS alloys also appeared. In the ZnCl2 treated bilayer, it was observed that the crystal structure of the CdZnS alloy changed from hexagonal to cubic phase. While similar grain structure was observed in the as deposited and the ZnCl2 treated samples; it was seen that CdCl2 treatment significantly affected the grain form and size. CdCl2 treatment resulted in a large increase of Cd-ratio and a more balanced increase Zn-ratio in ZnCl2 treatment. It was determined that ZnCl2 and CdCl2 treatments caused a decrease in the transmittance of the samples. PL spectroscopy revealed the presence of many structural defects such as interstitial zinc, sulfur vacancies, surface states, cadmium vacancies in all bilayer samples. Solar cells with ZnS/CdS, ZnS/CdS (CdCl2-treated) and ZnS/CdS (ZnCl2-treated) junction partners achieved efficiencies of 4.56%, 5.64% and 5.20%, respectively. Solar cell parameters showed that ZnCl2 treatment increased the FF value, while CdCl2 treatment improved the Voc value. An efficiency of 6.01% was obtained from the ZnS/CdS (CdCl2-treated)/CdTe/CdCl2 cell produced by obtaining the highest efficiency with the ZnS/CdS/CdCl2 junction partner. This cell revealed that applying CdCl2 treatment on CdTe significantly increased Voc and Jsc while deteriorating FF.
