GROWING Sb 2 Se 3 FILMS ENRICHED WITH SELENIUM USING CHEMICAL MOLECULAR BEAM DEPOSITION 1

This study explores the growth of Sb 2 Se 3 films on soda-lime glass (SLG) surfaces using the chemical molecular beam deposition (CMPD) method at a substrate temperature of 500°C. High-purity binary compounds, Sb 2 Se 3 and Se, were employed as source materials for film deposition. Scanning electron microscopy (SEM) was employed to investigate the morphological characteristics of the Sb 2 Se 3 films. Furthermore, the influence of temperature on the grain size and crystallographic orientation in selenium films was examined. Samples were obtained from a selenium source at temperatures of 370°C and 430°C. The results indicate that increasing the temperature of the selenium source results in the formation of larger grains and the presence of rod-shaped grains of Sb 2 Se 3 aligned parallel to the substrate. A sample obtained at 370°C exhibited grains larger than 2 µm in size, evenly distributed across the substrate surface, indicating a uniform growth process. In contrast, when the temperature of the selenium source was raised to 430°C, considerably larger grains measuring approximately 4 μ m were detected on the film surface substrate. X-ray diffraction analysis was conducted to gain insights into the crystalline phases and crystal structure of the Sb 2 Se 3 films synthesized under different temperatures of the selenium source. The X-ray diffraction patterns displayed prominent peaks corresponding to the crystallographic planes (221) and (211), indicating the presence of strong crystalline phases. Additionally, peaks such as (020), (120), and (310) were observed in the X-ray patterns, further confirming the crystallinity of the films.


INTRODUCTION
Antimony selenide (Sb 2 Se 3 ) has emerged as one of the most promising absorber materials for the development of nextgeneration thin-film solar cells, due to its outstanding photovoltaic performance.The remarkable properties of Sb 2 Se 3 , including its simple crystal structure, substantial absorption coefficient exceeding 10 5 cm -1 , ideal band gap within the 1.1-1.3eV range, and significant mobility, approximately 10 cm 2 V -1 s -1 [1], make it a highly attractive candidate for advanced thin-film solar cells.One distinct advantage of Sb 2 Se 3 , compared to more established thin-film solar cells, specifically Copper Indium Gallium Selenide (CuInGaSe(S) 4 , referred to as CIGS) and Cadmium Telluride (CdTe), is its cost-effectiveness.Both antimony (Sb) and selenium (Se), the constituent elements of Sb 2 Se 3 , are widely available and exhibit lower toxicity.As such, we can anticipate that Sb 2 Se 3 technology will become a serious competitor in the mass production of thin-film photovoltaic modules.It has been discovered that [hk1]-oriented (vertically oriented) Sb 2 Se 3 film is superior for efficient charge carrier transfer compared to the [hk0]-oriented Sb 2 Se 3 compound film.However, controlling the orientation of the thin film remains a significant hurdle to further enhancing the efficiency of Sb 2 Se 3 -based solar cells.It should be noted that during the synthesis of Sb 2 Se 3 films via physical methods, a considerable amount of Se is lost due to film decomposition into Sb, Se, and SbSe.This results in the formation of Se vacancies, which subsequently increase the density of recombination centers in the films [2].These changes have a negative impact on the optical and electrophysical properties of the solar cells.To mitigate this issue, researchers propose additional heat treatment in Se vapor.Zhiqiang Lee [2] has successfully produced thin film Sb 2 Se 3 using a co-evaporation method of Sb 2 Se 3 and Se [3,4], whilst Shongalova [5] has introduced a method for creating Sb 2 Se 3 films by sputtering, followed by "selenized" annealing in a H 2 Se gas atmosphere.These innovative solutions illustrate the ongoing advancements in the field, paving the way for the full realization of Sb 2 Se 3 potential in next-generation solar technology.
Sb 2 Se 3 films are used various methods precipitation: thermal evaporation [6][7], gas transport evaporation [8,9] method sublimation in a closed vacuum [10] and magnetron sputtering [11].In this work, first time to grows films Sb 2 Se 3 for solar cells by chemical molecular beam deposition (CMBD) method.In this study, we investigate the growth of Sb 2 Se 3 films on SLG substrates using the CMBD method.

MATERIALS AND METHODS
Installed technological mode optimal grow Sb 2 Se 3 films on surfaces SLG (soda-lime glass ) by the method chemical molecular beam precipitation (Fig. 1).The experimental system was prepared by purging hydrogen to eliminate atmospheric pollutants.The SLG substrates with dimensions of 2.0×2.0 cm 2 were used for film deposition.To obtain Sb 2 Se 3 films with enriched selenium content and stoichiometric composition, the partial pressure of Se in the steam phase was adjusted during the growth process.The substrate temperature was maintained at 500°C, while the temperatures of the source elements were varied within the ranges of 350°C to 430°C for Se and 700°C for Sb 2 Se 3 .The growth rate was controlled between 0.1 to 1 Å/sec, and a hydrogen flow rate of WH 2 = 20 cm 3 /min was maintained.Granules of Sb 2 Se 3 and high-purity Se (99.999%) were utilized as the source materials.These compounds were placed in separate containers within the experimental setup.The morphological properties of the films were examined using a scanning electron microscope (SEM-EVO MA 10).The film compositions were determined by energy-dispersive elemental analysis (EDX) using an Oxford Instrument Aztec Energy Advanced X-act SDD detector.The crystal structure and phase composition were analyzed using X-ray diffraction (XRD) with a Panalytical Empyrean diffract meter, employing CuKα radiation (λ = 1.5418Å) and 2θ measurements in the range of 20° to 80° with a step size of 0.01°.The phase composition analysis was conducted using the Joint Committee on Powder Diffraction Standards (JCPDS) database.This study investigates the influence of temperature on grain size and crystallographic orientation in selenium films.A sample was obtained from a selenium source at temperatures of 370°C and 430°C.The characterization of the samples was performed using microscopy techniques, and the results were analyzed to understand the relationship between temperature and the observed grain size and crystallographic orientation.Our findings indicate that increasing the temperature of the selenium source leads to the formation of larger grains and the presence of rod-shaped grains of Sb 2 Se 3 aligned parallel to the substrate.These observations are consistent with the collected data, which also revealed an increase in the peak texture coefficients (hk0) at the temperature of 430°C.
Upon analyzing the sample obtained at 370°C, grains larger than 2 µm in size were observed.These grains exhibited a uniform distribution across the substrate surface, indicating a uniform growth process.However, when the temperature of the selenium source was raised to 430°C, considerably larger grains measuring approximately 4 μm were detected on the film surface substrate.The increase in temperature led to the formation of larger grains, which can be attributed to enhanced diffusion and coalescence processes during film growth.
Furthermore, rod-shaped grains of Sb2Se3 were observed in the sample obtained at 430°C.These grains aligned themselves parallel to the substrate, as depicted in Figure 2. The formation of Sb 2 Se 3 grains can be attributed to the reaction between antimony (Sb) impurities present in the selenium source and the substrate material.The alignment of these rodshaped grains suggests an epitaxial growth mechanism on the substrate surface.
The XRD analysis revealed that the peak texture coefficients (hk0) began to exhibit an increase at the temperature of 430°C.This finding indicates a preferential crystallographic orientation in the film, which can be attributed to the growth conditions and the interaction between the deposited selenium and the substrate material.The increased peak texture coefficients further support the observed larger grain size and the presence of Sb 2 Se 3 rod-shaped grains.
These observations are consistent with our data, as the presence of larger grains can positively impact the performance of solar cells by reducing recombination losses.Larger grains tend to have fewer defects along their boundaries, which can lead to improved efficiency in converting solar energy.In conclusion, our results demonstrate that temperature influences grain size and texture in the selenium film.The larger grain size observed at higher temperatures suggests the potential for enhanced solar cell performance.
Table 1 presents the chemical composition of the elements in the deposited Sb 2 Se 3 films.The analysis using an energy dispersive elemental analyzer revealed that the Sb/Se atomic concentration ratio decreased as the selenium EEJP. 1 (2024) Takhirdjon M. Razikov, et al.
temperature increased from 350°C to 430°C, approaching the stoichiometric composition of Sb/Se≈0.66.This indicates that the selenium content in the Sb 2 Se 3 thin films increased with higher selenium flow.At a selenium source temperature of 350°C, the Sb 2 Se 3 film was selenium-poor.However, at higher temperatures, the compound films approached a stoichiometric composition with an Sb/Se ratio of 0.68, which was achieved at a selenium source temperature of 430°C.
It is evident that the temperature of the selenium source plays an important role in obtaining high-quality Sb 2 Se 3 films.Stoichiometric, vertically oriented Sb 2 Se 3 grains larger than 4 µm were successfully obtained at a selenium temperature of 430°C, which are considered beneficial for charge carrier transport.It is worth noting that Sb 2 Se 3 films exhibit p-type conductivity.However, some samples of Sb 2 Se 3 may exhibit ntype conductivity due to the presence of Sb impurities.Additionally, the presence of (V Se ) defects can also contribute to n-type conductivity or act as donors [12].The implications of the Sb/Se atomic concentration ratio approaching the stoichiometric composition in Sb 2 Se 3 films are significant.The stoichiometric composition represents the ideal ratio of antimony (Sb) to selenium (Se) atoms in Sb 2 Se 3 .When the Sb/Se ratio approaches this stoichiometric composition, the film exhibits optimal electrical properties.This means that the film is more likely to have the desired characteristics for its intended applications, such as solar cells.Achieving the stoichiometric composition helps in attaining the desired electronic band structure and charge transport properties.Reduced Defects: Deviations from the stoichiometric composition can introduce defects in the crystal structure of the material.By approaching the stoichiometric composition, the number of defects, such as vacancies or impurities, can be minimized.Fewer defects lead to improved electrical and optical properties, as defects act as recombination centers for charge carriers, reducing their lifetime and overall device performance.
Structural properties of Sb2Se3 films.Figure 3 present the outcomes of the X-ray diffraction analysis, providing insights into the crystalline phases and crystal structure of the Sb 2 Se 3 films synthesized under different temperatures of the selenium source.The X-ray patterns exhibit distinct features, with notable observations regarding the intensity variations of specific peaks in response to increasing temperature of the selenium source.The X-ray diffraction patterns display prominent peaks corresponding to the crystallographic planes ( 221) and (211), indicating the presence of strong crystalline Growing Sb 2 Se 3 Films Enriched with Selenium Using Chemical Molecular Beam Deposition EEJP. 1 (2024) phases.Additionally, peaks such as (020), (120), and (310), are also obviously in the X-ray patterns.Notably, these peak intensities demonstrate a dependence on the temperature of the selenium source, with alterations observed as the temperature increases.The selenium source temperature of T Se = 370°C, the XRD analysis reveals the disappearance of weak peaks, including (020), ( 120), (310), ( 230), ( 240), (002), and (320), while the strong peaks ( 221) and (211) remain raised.This suggests a distinct influence of the temperature on the crystal structure, leading to the elimination of certain crystallographic planes at temperatures up to T Se = 370°C.Furthermore, a subsequent increase in temperature to T Se = 430°C induces a decrease in the intensities of the ( 221) and (211) peaks, while the weak peaks (020), ( 120), (230), and (240) become significantly more pronounced.This temperature-dependent variation highlights the dynamic nature of the crystal structure and phase composition of the Sb 2 Se 3 films.Moreover, an additional observation is made at 2θ = 29.66°,where a low-intensity reflex is detected in correspondence to the (101) peak.This reflex indicates the formation of the Se phase, providing evidence of a distinct phase transition or phase presence within the Sb 2 Se 3 films under the given experimental conditions.In summary, the XRD analysis of the Sb 2 Se 3 films elucidated valuable information regarding their crystal structure and phase composition.The obtained results demonstrate the influence of the selenium source temperature on the intensities of specific peaks, emphasizing the temperature-dependent alterations in the crystal structure.Additionally, the identification of the Se phase further contributes to the understanding of the film's structural properties.To quantitate vela, study the orientation of Sb 2 Se 3 films , the texture coefficients (T C ) of diffraction peaks were calculated based on the following equation [13]: The intensities of the diffraction peaks, denoted as I (hkl) and I 0(hkl) , respectively, correspond to the measured and standard X-ray diffraction patterns of Sb 2 Se 3 (JCPDS 15-0861) for the crystallographic planes (hkl).The determination of the peak intensity is crucial for analyzing the crystal orientation and structural properties of the material under investigation.Notably, the texture coefficient, TK, associated with the diffraction peaks signifies the level of orientation prevalence along a specific direction.In the case of the examined samples, the high TK values observed for the diffraction peaks indicate a pronounced orientation in the corresponding direction.Interestingly, at a selenium source temperature of 370°C, the TC values for crystallographic planes (hk0) in our samples tend to decrease.This initial decrease suggests a deviation from the dominant orientation, possibly due to the effect of elevated temperature on the crystal lattice arrangement.However, as the temperature of the selenium source continues to rise 370°C, a subsequent increase in the TK values for the (hk0) planes is observed.The temperature of the selenium source plays a significant role in influencing the crystal orientation and can result in distinct variations in the diffraction patterns of Sb2Se3.Further investigation is necessary to comprehensively understand the underlying mechanisms behind these observed temperature-dependent changes in crystal orientation and their implications for the materials properties.

CONCLUSIONS
In this study, we investigated the effect of temperature on grain size and crystallographic orientation in selenium films.The results indicate that increasing the temperature of the selenium source leads to the formation of larger grains and the presence of rod-shaped grains of Sb2Se3 aligned parallel to the substrate.The observed grain sizes and crystallographic orientations are in line with the collected data, as evidenced by the increased peak texture coefficients at the temperature of 430°C.These findings contribute to a better understanding of the growth mechanisms and properties of selenium films, which can aid in the development of tailored thin film technologies for various applications.Further studies exploring the influence of other parameters on grain formation and crystallographic orientation are warranted to expand our knowledge in this field.At a selenium source temperature of 430°C, large rod-like grains can be observed on Cite as: T.M. Razikov, S.A. Muzafarova, R.T. Yuldoshov, Z.M. Khusanov, M.K. Khusanova, Z.S. Kenzhaeva, B.V. Ibragimova, East Eur.J. Phys. 1, Growing Sb 2 Se 3 Films Enriched with Selenium Using Chemical Molecular Beam Deposition EEJP. 1 (2024)

Figure 3 .
Figure 3. X-ray diffraction pattern of Sb2Se3 films at different temperatures of the selenium source

Table 1 .
Chemical compound Sb2Se3 films at various temperatures selenium source