Enhancing the Photovoltaic Performance of Cd_(1−x)Zn_xS Thin Films Using Seed Assistance and EDTA Treatment

Abstract

This research article provides a comprehensive investigation into the optoelectronic characteristics of three distinct types of cadmium sulfide (CdS) thin films, namely: (a) conventionally prepared CdS thin films using chemical bath deposition (CBD-CdS), (b) CdS thin films produced via chemical bath deposition with the inclusion of zinc (CBD-Cd_(1−x)Zn_xS, x = 0.3), and (c) CdS thin films synthesized using a seed-assisted approach, treated with ethylenediaminetetraacetic acid (EDTA), and incorporating zinc (ED/CBD + EDTA-Cd_(1−x)Zn_xS). The investigation reveals that the crystallite size of these thin films decreases upon the addition of EDTA to the reaction solution, leading to an increase in the inter-planar spacing and dislocation density. Furthermore, a blue shift in the transmittance edge of the ED/CBD + EDTA-Cd_(1−x)Zn_xS samples compared to CBD-CdS implies modifications in the band gaps of the deposited films. The incorporation of Zn²⁺ into the reaction solution results in an increased band gap value of up to 2.42 eV. This suggests that Cd_(1−x)Zn_xS thin films permit more efficient photon transmission compared to conventional CdS. Among the three types of films studied, ED/CBD + EDTA-Cd_(1−x)Zn_xS exhibits the highest optical band gap of 2.50 eV. This increase in the optical band gap is attributed to the smaller crystallite size and the splitting of the tail levels from the band structure. Additionally, the increment in the optical band gap leads to reduced light absorption at longer wavelengths, thereby enhancing the electrical properties. Notably, ED/CBD + EDTA-Cd_(1−x)Zn_xS thin films demonstrate improved photovoltaic performance in a photoelectrochemical (PEC) cell, characterized by enhanced open-circuit voltage (363 mV, V_OC), short-circuit current (35.35 μA, I_SC), and flat-band voltage (−692 mV, V_fb). These improvements are attributed to the better adhesion of CdS to the fluorine-doped tin oxide (FTO) substrate and improved inter-particle connectivity.

1. Introduction

Semiconductor materials find widespread practical applications across various fields due to their unique electrical and optical properties [1,2,3,4]. Among the diverse range of semiconductor materials, II-VI group semiconductors such as cadmium sulfide (CdS), cadmium telluride (CdTe), zinc selenide (ZnSe), and zinc sulfide (ZnS) have emerged as leading candidates for applications such as solar cells, light-emitting diodes, lasers, thin film transistors, piezoelectric devices, infrared detectors, and light detectors. This preference is attributed to their direct and wide band gaps, as well as high carrier effective mass [5,6,7].

In thin-film solar cell technologies, CdTe-based solar cells are the most commercially successful option due to their cost-effectiveness, efficiency, stability, and large-scale production. Within CdTe-based solar cells, the window layer plays a pivotal role in determining the solar cell’s overall efficiency. N-type CdS has proven to be an excellent choice for serving as the transparent window layer in CdTe-based heterojunction structures [8,9,10]. CdS itself possesses a direct band gap of 2.38 eV (in the cubic, metastable phase), 2.58 eV (in the wurtzite, stable phase) [11] and CdS is known for its stability and durability, which is essential for the long-term performance and reliability of CdTe solar cells. Conversely, CdS can passivate the grain boundaries within CdTe, resulting in a reduction in recombination and an improvement in the overall efficiency of the solar cell.

Generally, the thickness of the CdS layer should be less than 100 nm to transmit the bulk of the solar irradiation to the absorber material (CdTe) to achieve a high photocurrent density. However, narrowing down the thickness may result in the occurrence of pinholes, which can adversely affect the open circuit voltage and, hence, the conversion efficiency of the solar cells [12]. Therefore, selecting the most suitable deposition method that minimizes pinhole occurrence and yields a uniform film is crucial. CdS thin films can be deposited using many growth procedures such as electrodeposition (ED), chemical bath deposition (CBD), molecular beam epitaxy (MBE), spray pyrolysis, chemical vapor deposition (CVD), screen printing, and successive ionic layer adsorption and reaction (SILAR) deposition etc. [13,14,15]. However, reports on the use of combined growth techniques for the growth of CdS thin films and the study of their properties are rarely found in the literature [16,17].

Recent studies have indicated that the inclusion of ethylenediaminetetraacetic acid (EDTA) in the chemical bath deposition (CBD) process for CdS results in the formation of nanosized crystals. This, in turn, enhances the photoactivity of the CdS thin films by increasing the surface roughness and effective surface area [15]. Electrodeposited CdS (ED-CdS) thin films exhibit superior uniformity and adhere well to surfaces, particularly fluorine-doped tin oxide glass substrates [18,19]. Therefore, there is significant interest in exploring the combined deposition approach involving both ED-CdS and CBD-CdS with the addition of EDTA [16].

Another promising method for improving the optoelectrical properties of CdS thin films involves the incorporation of metal compounds such as In, Zn, or Ga [20]. Among these options, the incorporation of Zn into CdS thin films is particularly advantageous due to the almost similar ionic radii of Zn²⁺ (0.074 nm) and Cd²⁺ (0.095 nm) [21,22]. Additionally, the introduction of Zn²⁺ along with Cd²⁺ alters the optical transmittance of heterojunction solar cells by forming Cd_(1−x)Zn_xS ternary semiconductors. This alteration allows more photons to pass into the absorber layer when these films are employed in solar cells, thereby enhancing their efficiency [13,23].

It is postulated that the electrochemical process encompassing the electrodeposition of CdS, facilitated by seed crystals, and subsequent Zn doping within an EDTA-infused chemical bath (ED/CBD + EDTA-Cd_(1−x)Zn_xS), yields improved optoelectronic properties when compared to traditional methods involving CBD-CdS and Cd_(1−x)Zn_xS deposition. Remarkably, no prior scholarly work has been conducted utilizing these particular methodologies, as per the current state of knowledge held by the authors.

This investigation holds significance in the context of advancing the synthesis of materials at the nano- or micro-scale. The employment of seed-assisted growth in conjunction with EDTA treatment implies an elevated degree of precision and control at the nano-scale in the fabrication of Cd_(1−x)Zn_xS thin films. Additionally, this study contributes to the broader field of material engineering, where the exploration of the impacts of seed-assisted growth and EDTA treatment on Cd_(1−x)Zn_xS thin films entails deliberate modifications at the micro- and nano-scale to engineer materials with the desired properties, a pivotal facet of material engineering within the micro- and nano-scale domain.

Accordingly, we provide a comprehensive exploration of the improvements in the morphological, optical, and electronic properties of grown CdS thin films achieved by using an ED-CdS layer as a seed, along with incorporating EDTA and Zn. To investigate the impact of EDTA, the ED-CdS seed layer, and Zn incorporation on these properties, we conducted Grazing Incident X-ray Diffraction (GIXRD), UV-visible, C-V, and photoelectrochemical (PEC) cell measurements. Consequently, this study appears to introduce an innovative methodology (EDTA treatment) and a potentially unique combination of techniques. By extending the existing knowledge in this field, it provides insights that can potentially steer forthcoming research endeavors in the field of micro- and nano-scale.

2. Materials and Methods

All the chemicals used in this reporting study were analytical reagent grade. Deionized water was used for the preparation of all aqueous solutions. The chemicals and their respective specifications are shown in

Table 1. The experimental reagents and their specifications.

Chemical Compound	Purity Grade	Specification	Chemical Company
Cadmium Sulfate [3CdSO4.8H2O]	Analytical	99%	Breckland Scientific, Stafford, UK
Thiourea [CS(NH2)2]	Analytical	99%	MRS Scientific Inc., Wickford, UK
Ammonia Solution [NH4OH]	Analytical	35% w/w	Surechem Products Ltd., Ipswich, UK
Cadmium Chloride [CdCl2. 2½ H2O]	Analytical	98%	Sigma-Aldrich, St. Louis, MO, USA
Sodium Thiosulfate [Na2S2O3]	Analytical	97%	Baxter Smith Labs, California, CA, USA
Ethylenediaminetetraacetic Acid [EDTA]	Analytical	98%	Fischer Inorganics and Aromatics Ltd., Tamil Nadu, India
Zinc Sulfate (ZnSO4.7H2O)	Analytical	99.8%	VWR ProLab, Leuven, Belgium

. The FTO glass substrates (TEC 10, Sigma-Aldrich, St. Louis, MO, USA) were subjected to pre-deposition cleaning, which involved sequential steps. Initially, the substrates were cleansed using diluted HCl (ACS reagent, 37%, Sigma-Aldrich, USA) followed by rinsing with de-ionized water and subsequent ultrasound sonication. Later, the cleaning procedure continued using a series of organic solvents, namely acetone (ACS reagent, ≥99.5%, Sigma-Aldrich, USA), methanol (ACS reagent, ≥99.5%, Sigma-Aldrich, USA), and isopropanol (ACS reagent, ≥99.5%, Sigma-Aldrich, USA). Each solvent was utilized for cleaning the substrates at a temperature of 70 °C via immersion, and the substrates were properly dried using nitrogen gas afterward. [3,24,25].

2.1. Deposition of Chemical-Bath-Deposited CdS (CBD-CdS) Thin Films

The CBD-CdS thin films were deposited onto FTO glass substrates using 3CdSO₄.8H₂O (1 mM), CS(NH₂)₂ (2 mM), and a NH₄OH solution (1.1 mL) as reagents at a bath temperature of 80 °C, stirring the reaction solution at a rate of 200 rpm. The conducting glass substrates were positioned inside a beaker at an angle of 45° in the solution using a custom-designed Teflon sample holder. A detailed description of the methodology can be found in our previous publication [26].

2.2. Deposition of Chemical-Bath-Deposited Cd_1−xZn_xS (CBD-Cd_(1−x)Zn_xS; x = 0.3) Thin Films

Cd_1−xZn_xS (CBD-Cd_(1−x)Zn_xS; x = 0.3) films were grown on FTO glass substrates using the reagents; 3CdSO₄.8H₂O (0.47 mM), ZnSO₄.7H₂O (0.53 mM), CS(NH₂)₂ (2 mM), and NH₄OH solution (1.1 mL). The conducting glass substrates were positioned inside a beaker at an angle of 45° in the solution using a custom-designed Teflon sample holder. The bath temperature was maintained at 80 °C while stirring the reaction solution at a rate of 200 rpm. A detailed description of the methodology can be found in our previous publication [26].

2.3. Deposition of Seed-Assisted Cd_(1−x)Zn_xS with EDTA Treatment (x = 0.3 in the Reaction Solution)

First, a seed layer of ED-CdS was deposited onto the FTO glasses using CdCl_2. 2½ H₂O (0.05 M) and Na₂S₂O₃ (0.05 M) in a three-electrode system under a pH of 1–2 at a bath temperature of 60 °C. The seeds of ED-CdS were deposited for a duration of 3 min. A detailed description of the deposition of a ED-CdS seed can be found in our previous publication [16].

In order to deposit the Zn-incorporated EDTA-assisted CdS on top of the ED-CdS seed layer, the same chemical bath described in Section 2.2 was used with EDTA (0.2 mM) in the reaction vessel. All the other deposition parameters were kept as in Section 2.1 and Section 2.2. All the grown films under the three deposition methods were air-annealed at 200 °C for one hour in a tube furnace (Büchi TO-51).

3. Characterization

The grown CdS films underwent morphological characterization utilizing the Zeiss EVO|LS15 system. To assess the structural properties of the deposited films, GIXRD analysis was conducted employing a Panalytical diffractometer (Empyrean). The instrumental parameters employed for this characterization included CuKα radiation with a wavelength of 1.54184 Å and a 2° incident angle, operating at 40 kV and 40 mA. Optical characterizations were performed using a UV-1800 Shimadzu UV-vis spectrophotometer. To determine the thickness of the deposited CdS films, a Profilometer (XP-1) and SEM cross-sections were employed.

All PEC cell analyses were carried out on a Pt/0.1 mol.dm⁻³ Na₂S₂O₃/CdS/FTO setup, utilizing PEC Cell L01. The illuminated area of the CdS/electrolyte interface measured 0.25 cm². AM 1.5 simulated solar light irradiation was generated using a 150 W short-arc xenon lamp and directed onto the CdS/electrolyte junction. The same PEC cell configuration was employed for the capacitance–voltage (C–V) measurements, which were conducted using a sinusoidal signal of 1000 Hz and a voltage of 20 mV corresponding to the Ag/AgCl electrode.

4. Results and Discussion

4.1. Structural Characterization

Figure 1 displays the GIXRD diffractograms obtained for three distinct thin film samples: CBD-CdS, CBD-Cd_(1−x)Zn_xS, and ED/CBD + EDTA-Cd_(1−x)Zn_xS. For comparison, the XRD pattern of the FTO substrates is also included in Figure 1a, in addition to the XRD patterns of the CBD-CdS, CBD-Cd_(1−x)Zn_xS, and ED/CBD + EDTA-Cd_(1−x)Zn_xS thin films. In Figure 1b–d, the reflections are observed at specific 2θ angles of 25.07°, 26.46°, 28.32°, 44.10°, and 48.34°. These peaks correspond to (100), (002), (101), (110), and (103) planes of hexagonal CdS (JCPDS 98-009-5006 and 06-0314). Also, the 2θ peaks corresponding to the planes of (100) and (101) were found to broaden in both CBD-Cd_(1−x)Zn_xS and ED/CBD + EDTA-Cd_(1−x)Zn_xS compared to that of CBD-CdS. The variation in the diffraction peaks may be due to the poor crystallinity or the formation of nano-sized crystals resulting from Zn²⁺ incorporation into the CdS matrix [13,16,26]. No peaks of any other phase or impurity are noticed in the Zn-incorporated samples (Figure 1c,d). Thus, it can be determined that the films grown with Zn were not a blend of CdS and ZnS, but Cd_1−xZn_xS. The intensity of the (100), (101), (110), and (103) reflections of Cd_1−xZn_xS were found to be significantly increased.

The crystallite size was estimated using the highest intensity planes (100), (002), (101), (110), and (103) using the relation [27];

$$\beta \cos \theta =\frac{K\lambda }{D}+4\epsilon \sin \theta$$

(1)

where λ is the wavelength of the CuK_α radiation (λ = 1.54184 Å), θ is the Bragg angle, D is the average diameter of the grains, β is the FWHM of the diffraction peak, ε is the residual strain of the film, and K is the shape factor, which is approximately 0.94. The value of ε was obtained from the gradient of the βcosθ vs. sinθ plot. The obtained values of D, ε, and δ (dislocation density) for the films CBD-CdS, CBD-Cd_(1−x)Zn_xS, and ED/CBD + EDTA-Cd_(1−x)Zn_xS are tabulated in

Table 2. Variation of the average diameter of the grains, dislocation density, and residual strain of sample CBD-CdS, CBD-Cd_(1−x)Zn_xS, and ED/CBD + EDTA-Cd(_1−x)Zn_xS.

Sample	D (nm)	δ (1015 Line/m2)	ε Residual Strain
CBD-CdS	25.44	1.54	1.1790
CBD-Cd(1−x)ZnxS	13.65	5.24	−0.1236
ED/CBD + EDTA-Cd(1−x)ZnxS	12.25	6.69	−0.1272

.

Table 2 shows that the addition of Zn to the reaction bath has significantly changed the crystal size of the grown films. The alternation of the average crystallite size with the deposition method is also clear from the broadness of the XRD peak widths. This also reveals the increment in the lattice imperfections due to the increment in the internal micro-strain from CBD-CdS to ED/CBD + EDTA-Cd(_1−x)Zn_xS.

The crystallite size was found to decrease with the addition of EDTA to the reaction solution. Such a decrease in crystallite size may increase the inter-planar spacing as well as the dislocation density [28]. Hence, this variation found in the diffraction peak is an indication of different optical, electrical, as well as morphological changes in the grown films.

4.2. Optical Characterization

Figure 2 presents the transmittance spectra of CdS films grown using different deposition methods. The average transmittance values of CBD-Cd_(1−x)Zn_xS and ED/CBD + EDTA-Cd_(1−x)Zn_xS are higher compared to that of CBD-CdS in the wavelength region of 550–800 nm. Among the grown films, ED/CBD + EDTA-Cd_(1−x)Zn_xS produces the highest transmittance (>85%) in the wavelength range of 550–800 nm, as shown in Figure 2. Furthermore, the transmittance edge of the samples CBD-Cd_(1−x)Zn_xS to ED/CBD + EDTA-Cd_(1-x)Zn_xS was found to shift toward the lower wavelength region (blue shift) compared to CBD-CdS, indicating that the band gaps of the deposited films have been subjected to change. The blue shift of the band edge is desirable as it suggests an increase in the band gap of the thin film.

The optical band gap (E_g) values of the CdS films were obtained by extrapolating the linear (αhυ)² vs. hυ plots (Figure 3a) derived from the Stern relation [29,30,31,32,33,34]:

$$\alpha =\mathrm{A}\frac{{\left(\mathrm{h}\nu -{\mathrm{E}}_{\mathrm{g}}\right)}^{\raisebox{1ex}{$n$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}}{\mathrm{h}\nu }$$

(2)

where h is Planck’s constant, A is a constant, α is the optical absorption coefficient, and n is equal to 1 for CdS. Although the band gap of the grown CBD-CdS is 2.35 eV, it can be seen from

Table 3. Optical and electrical properties of grown CBD-CdS, CBD-Cd_(1−x)Zn_xS, and ED/CBD + EDTA-Cd_(1−x)Zn_xS samples.

Combination	Eg (eV)	VOC (mV)	ISC (µA)	ISC × VOC (µW)	Vfb (mV)	JSC (µAm−2)	ND (×1016 cm−3)	Thickness (nm)
CBD	2.35	169	9.74	1.65	−441	38.96	1.44	83
CBD-Cd(1-x)ZnxS	2.42	327	20.87	6.82	−664	83.48	2.65	87
ED/CBD + EDTA-Cd(1-x)ZnxS	2.50	363	35.35	12.82	−692	141.4	3.04	90

and Figure 3b that adding Zn²⁺ to the reaction solution helps increase the band gap value up to 2.42 eV. This suggests that Cd_(1−x)Zn_xS thin films permit more photons to transmit through the film compared to conventional CdS [35]. Out of the three different types of films grown, the highest optical band gap of 2.50 eV (Figure 3) was obtained in ED/CBD + EDTA-Cd_(1−x)Zn_xS. The increase in optical band gap can be related to the smaller crystallite size, as shown in Table 2, as well as the splitting of the tail levels from the band [36]. The increment in the optical band gap reduces the absorption of light in the regimes of a longer wavelength, which in turn enhances the electrical properties [28,30].

4.3. Electrical Characterization

4.3.1. PEC Cell Characterization

Figure 4 illustrates a plot depicting the open-circuit voltage (V_OC), short-circuit current (I_SC), and the product of V_OC and I_SC for the three distinct sets of grown films. It was observed that both the I_SC and V_OC values increased notably with the introduction of Zn and EDTA treatment. Specifically, the film ED/CBD + EDTA-Cd_(1−x)Zn_xS exhibited the highest I_SC values (as depicted in Figure 4a and detailed in Table 3). This enhancement in the I_SC values in the ED/CBD + EDTA-Cd_(1−x)Zn_xS films can be attributed to improved inter-particle connections and enhanced adherence of the ED-CdS seed to the FTO substrates compared to conventional CBD-CdS and CBD-Cd_(1−x)Zn_xS films, as previously discussed [15]. Furthermore, the superior photoactivity observed in the ED/CBD + EDTA-Cd_(1−x)Zn_xS film can be attributed to the well-interconnected network structure, which facilitates the efficient flow of charge carriers.

4.3.2. C-V Characterization

The flat-band potential (V_fb) and carrier concentration (N_D) of the deposited CdS films were obtained (Table 3 and Figure 5a) from the X-axis intercept and the gradient of the linear fit of the Mott–Schottky equation used [2,3,37,38].

$$\frac{1}{C^2}=\frac{2}{A\epsilon {\epsilon }_0{N}_D}(V-V_{fb}-\frac{kT}{e})$$

(3)

In the given equations, “e” represents the charge of an electron, “ε” (with a value of 8.5) denotes the dielectric constant, “ε₀” stands for the permittivity in a vacuum, “A” is the area of the depletion region, “k” is the Boltzmann constant, and “T” is the absolute temperature [39]. Although not shown, the Mott–Schottky plots confirmed the n-type behavior exhibited by all the Cd_(1−x)Zn_xS thin films fabricated in this study.

The flat-band potential and carrier concentration were observed to be at their lowest levels in the case of the conventional CBD-CdS films. Conversely, the improved net donor density (N_D) in the ED/CBD + EDTA-Cd_(1−x)Zn_xS film, as evident in Table 3, can be linked to the enhancement of the I_SC value. Notably, ED/CBD + EDTA-Cd_(1−x)Zn_xS exhibited the highest flat-band voltage (V_fb) among all the grown CdS films. The higher V_OC observed in films incorporating zinc (Zn) can be attributed to the increased energy gap (E_g) and V_fb, as shown in Table 3.

The rise in V_fb in the films incorporating Zn may be attributed to the formation of donor levels that effectively shift the relative energy band positions, leading to increased band bending and subsequently an elevated V_OC, as depicted in Figure 4b. The presence of distinct V_fb values supports the idea of varying relative conduction band levels within the grown CdS thin films, warranting further investigation into their energy band structures.

In typical unbiased n-type semiconductors, it is reasonable to assume a flat potential near the position of the bottom of the conduction band (E_CB) [40]. Utilizing E_CB as a reference point, it becomes possible to determine the valence band-edge potential (E_VB) of the deposited thin films [41,42].

E_VB = E_CB + E_g

(4)

The investigated energy band structure with respect to the Ag/AgCl is shown in Figure 5b. The figure shows the presence of different energy band levels in the grown films. The existence of different energy band levels in a material suggests the possibility of overcoming energy spikes in the depletion region in a p-n junction [15].

4.4. Morphological Characterization

Figure 6a–c shows the SEM images of CBD-CdS, CBD-Cd_(1−x)Zn_xS, and ED/CBD + EDTA-Cd_(1−x)Zn_xS, respectively. The CBD-CdS films show uniform and smooth clusters without creaks or apparent pinholes and cover the glass substrate appreciably well, as seen in Figure 6a. With the addition of Zn²⁺ into the reaction solution (x = 0.3), small uniform grains with well-defined grain boundaries were found to form (Figure 6b), potentially increasing the roughness. Hence, the effective surface area of the Zn-incorporated films enhanced the I_SC values (Table 3). Figure 6c shows an SEM image of the ED/CBD + EDTA-Cd_(1−x)Zn_xS film, which consists of some apparent spherical features and is clearly different from the other two types of films grown. The SEM images of ED/CBD + EDTA-Cd_(1−x)Zn_xS show more uniform coagulates associated with CBD and CBD-Cd_(1−x)Zn_xS, suggesting that the ED/CBD layer has greatly influenced the morphology of the CBD-CdS layer. Moreover, it is also found in the literature that the electrochemical deposition gives CdS in the hexagonal phase improved uniformity, packing, and better attachment to the FTO [8,43]. This could also be a reason for the improved I_SC values in the ED/CBD + EDTA-Cd_1−xZn_xS system.

5. Conclusions

This study comprehensively evaluates thin films, emphasizing their structural, optical, and electrical attributes influenced by varying deposition techniques. The GIXRD patterns of CBD-CdS, CBD-Cd_(1−x)Zn_xS, and ED/CBD + EDTA-Cd_(1−x)Zn_xS films reveal distinctive alterations in the films’ crystallinity and grain morphology. These X-ray diffraction patterns unveil essential insights into the structural evolution brought about by the deposition processes.

The incorporation of zinc (Zn) in conjunction with EDTA treatment in seed-assisted CdS thin films induces a blue shift in the absorption edge, setting them apart from their pure CdS counterparts. This shift significantly modifies the optical band gap, elevating it from 2.35 to 2.50 eV. These values exhibit a consistent increment as we transition from CBD-CdS to CBD-Cd_(1−x)Zn_xS, culminating in the ED/CBD + EDTA-Cd_(1−x)Zn_xS film. This rise in the band gap is primarily ascribed to the reduction in crystallite size and consequential shifts in energy levels. These alterations, in turn, influence light absorption and electrical characteristics, making them pivotal factors in the films’ performance. Accordingly, when comparing CBD-Cd_(1−x)Zn_xS to CBD-CdS, a noteworthy enhancement in key photovoltaic parameters was evident. Specifically, open-circuit voltage (V_OC), short-circuit current density (J_sc), and flat-band voltage (V_fb) experienced substantial increments of 93%, 114%, and 50%, respectively, in the case of CBD-Cd_(1−x)Zn_xS in contrast to CBD-CdS. A similar trend was observed with ED/CBD + EDTA-Cd_(1−x)Zn_xS, showcasing remarkable improvements with increases of 114%, 263%, and 57% for V_OC, J_sc, and V_fb, respectively, when compared to CBD-CdS. Therefore, it can be stated that the deposition method employed influences the relative energy band positions. ED/CBD + EDTA-Cd_(1−x)Zn_xS emerges as the leader in terms of V_fb, in agreement with the significant shift in energy band positions and well-connected network structure. These shifts bear far-reaching implications for the energy band structures of the films.

The exceptional optoelectrical characteristics observed in ED/CBD + EDTA-Cd_(1−x)Zn_xS can be attributed to several contributing factors, as initially postulated. These factors include superior adhesion of CdS to the FTO (fluorine-doped tin oxide) substrate, enhanced carrier concentrations, unique spherical features, and improved inter-particle connectivity.

These findings contribute to the current body of knowledge and can potentially guide future research in the micro-and nano-scale domain. The impact of this research extends beyond the laboratory, holding promise for advanced semiconductor technology and photovoltaics applications. In summary, the synergistic combination of Zn incorporation and EDTA treatment in seed-assisted CdS thin films presents a compelling avenue for optimizing their optoelectronic properties, with far-reaching implications for emerging micro- and nano-scale technologies.