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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, Emin
Among 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.
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, Emin
In 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.
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, Emin
CdSexTe1-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.
Düşük Tellür Katkılı CuInGaSe2 İnce Filmlerin Yapısal Özelliklerinin İncelenmesi
(2019) Atasoy, Yavuz
Bu çalışmada Cu(In,Ga)(Se1-yTey)2 ince filmleri, külçe formundaki yapının elektron demeti ile buharlaştırılıp yüksek sıcaklıkta tavlanması ile elde edildi. Örneklerin X-ışını kırınım desenleri (XRD), Raman spektrumları, yüzey görüntüleri ile atomik konsantrasyon ölçümleri alınarak katkısız ve düşük Te katkılı örneklerin yapısal özellikleri ayrıntılı olarak incelenerek karşılaştırıldı. XRD desenlerinde, katkısız CIGS ince filminde, Cu(In,Ga)Se2 ve CuIn3Se5 gibi bir faz ayrışımının ortaya çıktığı, Te katkısı ile beraber faz ayrışımının ortadan kalktığı görüldü. Örneklere ait A1 Raman modlarının deneysel değerleri, teorik bir yaklaşımla elde edilen değerler ile karşılaştırıldı. Yüzey fotoğrafları incelendiğinde, Te katkısı ile beraber film yüzeyinin daha düzgün (uniform) hale geldiği ve tanelerin mikron-altı boyutlarında oluştuğu görüldü. Benzer şekilde, yapıdaki kompozisyon profilinin iyileştiği (Ga miktarının arttığı) ve hedeflenen miktarda Te’ün neredeyse yapıya girdiği görüldü.
Effect of annealing temperature on the microstructural and optical properties of newly developed (Ag,Cu)2Zn(Sn,Ge)Se4 thin films
(Springer Heidelberg, 2022) Atasoy, Yavuz
In this study, ACZTGSe thin films were fabricated by two-stage method to understand the effect of Ag and Ge incorporation in CZTSe system for the first time. For this purpose, sputtered (Ag-Cu-Zn-Sn-Ge)/evaporated (Se) precursor stacks were selenized at elevated temperatures (500-600 degrees C) for 3 min in rapid thermal processing system. The atomic ratios of the samples were adjusted to Ag/(Ag + Cu) = 0.10 and Ge/(Ge + Sn) = 0.05 and 0.30. The chemical composition of the films changed with the reaction temperature and by the degree of Ag-Ge co-doping. Moreover, Ge loss was more pronounced than Sn loss in the films due to the vapor pressure differences. Kesterite pure phase were acquired for CZTSe and ACZTGSe thin films after annealing treatment applied at 550 degrees C. Both XRD and Raman results revealed that Ag and Ge co-doped CZTSe thin films were successfully prepared. According to cross-sectional and surface images of the samples, it was deduced that incorporation of Ag and Ge into CZTSe lead to grain growth due to the liquid-assisted growth mechanism which was triggered by either Ag or Ge-based phases which acted as a fluxing agent. The band gap values shifted from 1.04 eV (CZTSe) to 1.14 eV (ACZTG(0.23)Se) for the thin films grown at 550 degrees C.
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, Emin
High 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.
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, Emin
Effects 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.
Employing pre-annealing as a control tool for alloying in CdSeTe/ CdTe stacks produced by evaporation in vacuum
(Academic Press Ltd- Elsevier Science Ltd, 2024) Ciris, Ali; Atasoy, Yavuz; Bacaksiz, Emin
Alloying plays a critical role in CdSeTe/CdTe stacks used as absorber structure in high efficiency solar cells. In this study, the effect of pre-annealing between CdSeTe and CdTe on the structural and optical properties of stacks was examined in detail. After the CdSeTe layers (before CdTe) were grown by vacuum evaporation, pre-annealing was applied at moderate temperatures in the range of 200 degrees C-300 degrees C. According to both XRD patterns and Raman spectra, a clear effect of preannealing temperature on alloying ratios and phase formations between CdSeTe and CdTe was ascertained. It was observed from the surface images that the change in pre-annealing temperature affected the grain sizes and morphology, depending on the Se ratios in the alloying. It was found that the transmission spectrum shifted to the long wavelength region with the change in crystallization as a result of pre-annealing. In the PL spectra, the presence of transitions related to the phase structures revealed by the XRD results was detected. In consequence, pre-annealing at 250 degrees C presented more promising results for potential CdTe cell applications.
Enhancement of the response speed of CIGS-based photodetector by Te-doping
(Elsevier Science Sa, 2024) Yilmaz, Salih; Basol, Bulent M.; Atasoy, Yavuz; Polat, Ismail; Kucukomeroglu, Tayfur; Bacaksiz, Emin
Cu(In,Ga)Se2 (CIGS) based devices are promising candidates for high performance photodetector applications. The present work investigated the effects of Te-doping on the properties of CIGS layers and studied the performance of photodetectors (PDs) fabricated on these films. The films were vacuum evaporated on glass substrates and their morphological, structural and optical properties were evaluated after an annealing step at 550 degrees C. Morphological data indicated that undoped CIGS films had non-uniform surface features with large grains separated by nanoparticles. Addition of 6.6 % Te improved the morphology and yielded a smoother layer. Further increase in Te concentration showed appreciable reduction in surface feature size and shape. X-ray diffraction patterns showed that increasing the Te amount in CIGS caused a shift in the XRD peaks towards smaller angles pointing to replacement of Se atoms by Te. Peak splitting at higher Te samples suggested a graded structure with Se and Te amounts changing through the thickness of the film. Raman analysis demonstrated formation of CuInGa(Se,Te)2 (CIGST) compound. According to Tauc's approximation, CIGS films with and without Te atoms possessed two energy band gaps of Eg1 and Eg2 that were in the ranges of 1.10-1.28 eV and 1.16-1.36 eV, respectively. Electrical data obtained from photodetector devices showed a responsivity of 4.44x10- 1 A/W and a detectivity of 8.01x107 Jones for Te-free material, while the rise/fall times were measured as 34/148 ms. A much faster response speed of 19/20 ms was reached for devices fabricated on films with 10.2 % Te. This work demonstrated, for the first time, the fabrication low-cost and high-performance metalsemiconductor-metal (MSM) type CIGST-based PDs.
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, Emin
In 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.
Improved CZTSe solar cell efficiency via silver and germanium alloying
(Pergamon-Elsevier Science Ltd, 2024) Atasoy, Yavuz; Bacaksiz, Emin; Ciris, Ali; Olgar, Mehmet Ali; Zan, Recep; Ali, Ahmed M. J. Al-dala; Kucukomeroglu, Tayfur
In this study, we report systematic investigation of the effects of Ag and Ge alloying on properties of CZTSe layers, as well as, on the performance of solar cells fabricated using these films. In this context, Ag-Ge doped CZTSe layers were produced by selenization of Cu/Sn/Zn/Cu/(Ag,Ge)/Se precursor stack structures using rapid thermal processing. All precursor stacks and the Ag-Ge doped CZTSe films obtained after selenization exhibited (Cu + Ag)-poor and Zn-rich chemical composition. XRD studies demonstrated pure kesterite phase for all reacted films. Raman spectra confirmed this finding. Cross-sectional SEMs showed large grain structure, which resulted from Ag-Se and Ge-Se liquid phase formation that assisted crystal growth during high temperature annealing. While a slight Ag-front-gradient was achieved in Ag-doped CZTSe film, the Ag gradient disappeared with incorporation of Ge into the lattice. Addition of Ge formed a gradient within the material such that near-contact region was more Ge-rich. Solar cells fabricated using films with various compositions demonstrated that double doping CZTSe with both Ag and Ge improved the device efficiency from about 5 % to over 8 %.
Improving device performance of sputtered CZTSe based solar cells by Manganese doping
(Elsevier, 2024) Atasoy, Yavuz; Basol, Bulent M.; Bacaksiz, Emin
Despite many efforts, Cu2ZnSnSe4 (CZTSe) based solar cells have remained relatively low efficiency compared to other thin film-based devices. One of the prevalent strategies used to improve cell performance in CZTSe is cation substitution. In this contribution, the effects of substituting Mn for Zn on CZTSe solar cell performance were systematically examined. Samples with various Mn content were grown by a two-stage method involving high temperature annealing of precursor layers comprising Cu, Zn, Sn, Mn and Se. All of the samples were found to have Cu-poor and (Zn + Mn)-rich or nearly stoichometric compositions. They crystalized in kesterite phase irrespective of the Mn content as confirmed by X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) measurements. The highest efficiency solar cell (5.56%) was obtained employing the 5% Mn doped CZTSe absorber. This film was found to have improved microstructure and reduced defect density. This is the first report on over 5% efficient kesterite thin film solar cell fabricated on a Cu2Mn0.05Zn0.95SnSe4 absorber layer.
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 Ali
In 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.
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, Emin
The 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.
Sputtered Mo-bilayer thin films with reduced thickness and improved electrical resistivity
(Iop Publishing Ltd, 2019) Keles, Filiz; Atasoy, Yavuz; Seyhan, Ayse
In this study, Mo-bilayer film, the thickness of which was reduced to approximately 270 nm with a very low resistivity of 14 mu Omega.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.
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, Emin
In 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.

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