Optoelectronic Study of Solution Grown Sb2Se3 Thin Films

Bharat G. Thakare¹, Niranjan S. Samudre¹, Amol R. Naikda¹, Navnath M. Yajgar¹, Bhushan B. Chaudhari¹, Sudam D. Chavhan¹*, R. R. Ahire¹, Sachin J. Nandre²*,

¹ Department of Physics, S. G. Patil Art’s, Science and Commerce College, Sakri (Maharashtra)

² Department of Physics, U. P. College, Dahivel (Maharashtra)

*Email: – sachinjnandre@gmail.com , sudam1578@gmail.com

Abstract

This study explores the optoelectronic properties of Sb₂Se₃ thin films grown via chemical bath deposition (CBD), selenosulphate solution prepared by refluxing method, alongside antimony potassium tartrate solution complexed with triethanolamine and ammonia, diluted to 100 mL. Clean glass substrates underwent room-temperature deposition for 4 hours in darkness to ensure controlled nucleation, followed by rinsing with deionized water, drying hot air using dryer. Optical and electrical properties of chemically deposited Sb₂Se₃ thin films were systematically investigated to assess their suitability. Transmittance analysis in the wavelength range of 500–1000 nm reveals moderate transparency (~35–40%) in the near-infrared region, while a sharp decrease in transmittance below ~800 nm indicates a distinct absorption edge. Correspondingly, the absorbance spectrum exhibits strong absorption in the visible region (500–700 nm), confirming efficient photon harvesting with absorption coefficients exceeding 10⁴–10⁵ cm⁻¹. The optical bandgap, determined using a Tauc plot for direct allowed transitions, is found to be approximately 1.4 eV, which lies within the optimal range for single-junction solar cell applications. Electrical characterization of the as-deposited films shows linear and symmetric I–V behavior with current increasing from 0 to ~35 pA over 0–14 V, indicating ohmic conduction dominated by high series resistance. This behavior is attributed to intrinsic film resistance arising from amorphous regions, selenium vacancies, and poor inter-grain connectivity typical of unannealed solution-grown films. The absence of rectifying characteristics suggests an incomplete photovoltaic device lacking a p–n junction. Post-deposition treatments such as annealing or selenization are expected to improve crystallinity, reduce defect density, and enable efficient charge collection for enhanced solar cell performance.

Keywords: –Reflux; TEA; Sb₂Se₃; CBD; Optical; I-V.

Introduction

The rapid growth of optoelectronic and photovoltaic technologies has intensified the search for efficient, low-cost, and environmentally benign semiconductor materials. In this context, antimony selenide (Sb₂Se₃) has emerged as a promising absorber material owing to its suitable band gap, high optical absorption coefficient, and favorable charge transport properties [1]. Sb₂Se₃ is a V–VI compound semiconductor composed of earth-abundant and non-toxic elements [2,3], which makes it attractive for sustainable large-scale optoelectronic applications.Sb₂Se₃ crystallizes in an orthorhombic structure consisting of one-dimensional (Sb₄Se₆)ₙ ribbons held together by van der Waals forces. This unique structural arrangement leads to strong anisotropy in optical and electrical properties and contributes to efficient light absorption and carrier transport along preferred crystallographic directions [4,5]. The material exhibits a direct band gap in the range of 1.1–1.3 eV and an absorption coefficient exceeding 10⁵ cm⁻¹ in the visible region, which is well suited for solar energy harvesting and photodetection devices [6].The optoelectronic properties of Sb₂Se₃ thin films are highly dependent on the deposition technique and growth parameters. Various vacuum-based methods such as thermal evaporation, sputtering, and vapor transport deposition have been employed to fabricate Sb₂Se₃ films with controlled properties [7, 8]. However, these methods often involve high processing temperatures, complex instrumentation, and increased fabrication costs. Consequently, solution-based deposition techniques have attracted considerable interest as viable alternatives due to their simplicity, low energy consumption, and potential for large-area and flexible substrates [9].Solution growth methods, including chemical bath deposition, hydrothermal synthesis, and spin coating, offer enhanced control over film morphology, stoichiometry, and thickness through optimization of precursor concentration, bath temperature, deposition time, and solution chemistry [10, 11, 12]. These parameters play a crucial role in determining the optical absorption behavior, band gap energy, carrier concentration, and electrical conductivity of Sb₂Se₃ thin films. Systematic optoelectronic studies of solution-grown Sb₂Se₃ are therefore essential to establish correlations between growth conditions and functional properties.In view of these considerations, the present study focuses on the optoelectronic investigation of solution-grown Sb₂Se₃ thin films. Detailed analysis of optical properties such as absorbance, transmittance, and band gap energy, along with electrical characteristics, provides valuable insight into the potential of these films for optoelectronic and photovoltaic applications [13, 14, 15]. Understanding and optimizing these properties is a key step toward the development of efficient, low-cost Sb₂Se₃-based devices.

Experimental Work

Materials. Antimony Potassium Tartrate Hemihydrate (C₄H₄O₇KSb.1/2H₂O; Extra pure AR, 99.5%-Sisco Research Laboratories Pvt. Ltd.), Selenium Metal Pellets (Se 99.999%), Sodium Sulphite Anhydrous (Na₂SO₃; AR-98%), Triethanolamine (C₆H₁₅NO₃; Extra pure 98%), Ammonia Solution (NH₄OH; Extra pure 30%), Acetone and Isopropanol Loba Chemie Pvt. Ltd. were used as precursors, reducing agents, complexing agents, and pH adjusters, respectively. Acetone and Isopropanol Loba Chemie Pvt. Ltd.) served as solvents for substrate cleaning and post-deposition rinsing. All chemicals were used as received without further purification.

Synthesis of Sb₂Se₃

Soda-lime glass substrates (dimensions: 75 mm × 25 mm × 1 mm) were meticulously cleaned prior to deposition to ensure a contamination-free surface[16]. The cleaning protocol involved sequential ultrasonic treatment in the following sequence: (i) a mild detergent solution (e.g., Labolene) for 5 min to remove organic residues; (ii) double-distilled water for 5 min; (iii) ethanol (99.9% purity) for 5 min; and (iv) isopropanol (99.7% purity) for 5 min. After each ultrasonication step, substrates were thoroughly rinsed with copious amounts of DDW to eliminate residual contaminants and prevent cross-contamination. The cleaned substrates were then dried using a gentle nitrogen gas blow to minimize particulate redeposition, followed by UV-ozone treatment for 10 minutes to enhance surface hydrophilicity and remove any remaining adventitious carbon. Finally, the prepared substrates were stored in a dust-free laminar flow cabinet until use for thin film deposition.The selenide source, 0.4 M sodium selenosulphate solution, was synthesized by refluxing 100 mL of 1 M sodium sulfite solution with excess selenium metal pellets (Se, 99.999% purity) at 90°C for 6 hours under constant stirring, adapting the procedure reported by Rodriguez-Lazcano et al. [17]. In a separate 100 mL beaker, 0.12 M of antimony potassium tartrate hemihydrate was dissolved in 32 mL of DDW with magnetic stirring until a homogeneous clear solution. To this, 3 mL of triethanolamine was added as a complexing agent, followed by 15 mL of 30% ammonia solution to adjust pH and stabilize the Sb-complex. The mixture was stirred vigorously for 10 minutes. Subsequently, 12 mL of the freshly prepared 0.2 M solution was introduced dropwise, and DDW was added to adjust the total volume to 100 mL, yielding the final chemical bath deposition (CBD) precursor solution.Cleaned glass substrates were vertically immersed in the chemical bath with the bath covered in aluminium foil to prevent photodegradation of the selenosulphate precursor. The deposition was conducted in a dark environment at room temperature (24 °C) for 4 hours to promote controlled nucleation and growth of the Sb₂Se₃ thin film via the CBD mechanism. Upon completion, the substrate was gently removed from the bath and rinsed thoroughly with DDW to wash away loosely adhered particles, residual precursors, and byproducts. The film was initially dried using a hot air dryer at 60°C, followed by purging with high-purity nitrogen gas to ensure uniform drying without mechanical damage.The processed substrate was allowed optical, and electrical characterization.

Fig. 1 Experimental Set-up of CBD at

room temperature

Result and Discussion: The Fig. 2 (a) plots transmittance (%) on the y-axis (0–40%) against wavelength (nm) on the x-axis (500–1000 nm), with a blue curve labeled “Sb₂Se₃”. The film shows moderate transparency starting at ~35–40% around 900–1000 nm in the near-infrared (NIR) region, where longer wavelengths pass through with minimal absorption. As wavelength decreases toward the visible range (500–800 nm), transmittance drops sharply from ~30% at 850 nm to near 0% below 700 nm, indicating a distinct absorption edge. This behaviour reflects the fundamental absorption process where photons with energy exceeding the bandgap (~1.5 eV, corresponding to ~825 nm) are strongly absorbed, while lower-energy NIR photons transmit—ideal for top-cell applications in tandem solar cells or single-junction devices targeting AM1.5G spectrum utilization.Directly adjacent Fig. 2 (b) absorbance (arbitrary units, 0–1.4) versus wavelength (500–1000 nm) is shown in red (“Sb₂Se₃”),

displaying the inverse trend: near-zero absorbance beyond 900 nm, followed by a steep rise commencing around 800 nm. Peak absorbance (>1.2 units) occurs in the 500–700 nm visible range, plateauing at high values that imply absorption coefficients (α) exceeding 10⁴–10⁵ cm⁻¹—characteristic of direct bandgap chalcogenides like Sb₂Se₃. This profile confirms efficient photon capture from blue-green to red light, with the onset aligning precisely with the transmittance edge, as expected from the Beer-Lambert law (T = e^{-αd}, where d is film thickness, typically 200–1000 nm for chemical bath deposited films).The Fig. 2 (c)employs a Tauc representation for direct allowed transitions, plotting (αhν)² (units: cm⁻² eV², 0–3) versus photon energy (hν, 1.2–1.8 eV) in green (“Sb₂Se₃, Eg=1.4 eV”). Here, α is derived from absorbance via α = (ln(1/T))/d, assuming uniform thickness. The curve remains flat near zero below ~1.4 eV (sub-bandgap scattering), then rises linearly with a steep slope above 1.4 eV, characteristic of direct interband transitions described by the Tauc equation: (αhν)² = A(hν – Eg), where A is a constant and Eg is the optical bandgap. Extrapolating the linear portion (tangent from ~1.45–1.65 eV) intersects the x-axis at precisely 1.4 eV, confirming the film’s direct bandgap. This value falls within the optimal range (1.1–1.6 eV) for single-junction photovoltaics. The I-V characteristic of as-deposited Sb₂Se₃ thin films, shown in Fig. 2 (d)the attached plot, displays linear ohmic behavior with current increasing steadily from 0 mA at 0 V to approximately 35 mA at 14 V, reflecting symmetric conduction without rectification. This indicates high series resistance dominated by the intrinsic absorber layer—typical for unannealed chemical bath deposited films featuring amorphous regions, Se vacancies, and poor inter-grain contacts that limit charge transport. For photovoltaic applications, such ohmic response signals an incomplete device lacking a p-n junction (e.g., with n-CdS), as ideal solar cells require diode-like rectification to generate Voc, Jsc, and fill factor under illumination; annealing or selenization treatments typically enhance crystallinity, reduce defects, and enable carrier collection along the ribbon-like structure for efficiencies reaching 3-10%.[18, 19, 20]​

Conclusion

In summary, this work successfully demonstrated a reproducible chemical bath deposition route for Sb₂Se₃ thin films using in-house sodium selenosulphate and antimony potassium tartrate precursors, yielding uniform coatings at room temperature with controlled post-processing. Optical spectra confirmed strong visible absorption (α > 10⁴ cm⁻¹), NIR transparency (35-40%), and a direct bandgap of 1.4 eV-optimally matched to AM1.5G illumination for photovoltaic absorbers—while the linear ohmic I-V response highlighted intrinsic high resistivity from defects in as-deposited films, underscoring the need for annealing to form rectifying junctions and boost carrier collection. These findings validate solution-processing viability for low-cost Sb₂Se₃ optoelectronics, paving the way for tandem cell integration and efficiency gains beyond 10% through targeted defect passivation and texturing.

Acknowledgements

One of the authors, Mr. Bharat Thakare, expresses sincere gratitude to the Trible Research and Training Institute, Pune, for financial support through a Maharashtra Government-sponsored fellowship during his Ph.D. research. The authors also extend their heartfelt thanks to the Principal of S.G. Patil ASC College, Sakri, for providing access to essential research facilities and infrastructure that enabled this work.

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