Electrochemical Synthesis of Polyaniline and Sheet-like Structure of Molybdenum Selenide (PANI@2D-MoSe₂) Binary Composite for Solar Cell Applications

Abstract

In this work, a promising material of polyaniline (PANI) and two-dimensional molybdenum diselenides consisting of a PANI@2D-MoSe₂ binary composite was prepared by an electrochemical polymerization ethod. The as-prepared PANI@2D-MoSe₂, the polymer covered in the sheet-like structure of 2D-MoSe₂ surface morphologies, was observed through FE-SEM and HR-TEM studies. The SAED pattern of PANI@2D-MoSe₂ was observed to be in an octahedral phase. The octahedral crystalline phase was also confirmed based on the XRD pattern. In addition, EIS studies of the PANI@2D-MoSe₂ binary composite counter electrode (CE) revealed the highest electrical conductivity of 3.47 × 10⁻⁴ S/cm at room temperature. The DSSCs assembled the PANI@2D-MoSe₂ CE, which amounted to a 7.38% efficiency. Pristine PANI, 2D-MoSe₂, and Pt CEs exhibited efficiencies of 5.07%, 5.82%, and 6.61%. The PANI integrated with 2D (MoSe) combines influences of conductivity and stability for future energy conversion technologies.

1. Introduction

Dye-sensitized solar cells (DSSCs) are low in cost, easy to fabricate, and have superior efficiency compared to other devices [1,2,3]. DSSCs consist of a dye-sensitized TiO₂ as a photo-anode and a polymer-based I⁻/I³⁻ redox couple. In most high-efficiency solar cells, Pt is used as the counter electrode (CE) because of its higher conductivity, electrocatalytic activity, and better efficiency compared to other CE materials [4]. Hence, the Pt electrode is used in the fabrication of DSSCs; however, some demerits, such as the corrosion of the counter electrode and the instability of liquid electrolyte medium, make Pt-based CEs very difficult to use, with 40% of the cost alone being spent on CE preparation [5]. Several research reports have involved developments in the fields of lowering the cost and gaining higher efficiency in CEs, such as through the use of carbon-based materials [6], polymers [7], and polymer-based composites [8]. Several polymer-based composites have been used as CEs in DSSCs.

In recent years, the PANI-TMCs of PANI-WS₂, PANI-MoS₂, and PANI-WSe₂ composites were used as CEs for DSSCs [9,10,11]. Among the composites, the PANI@2D MoSe2 composite has several merits as a CE. Due to the positively charged PANI attached to the negatively charged MoSe₂, it provides a better active surface area, excellent electrical and electrocatalytic properties, and gives better stability and efficiency to the DSSC device. Additionally, various methods were used in the preparation of PANI@2D MoSe₂ composite CEs for DSSCs like hydrothermal [12], solvothermal [13], chemical [14], and electrochemical polymerization methods [15]. Comparatively, among these methods, electrochemical polymerization techniques are one of the best choices for energy conversion technologies, due to the merits of their facile and controllable synthesis, their uniform deposition onto an FTO glass plate, and the fact that the obtained composite appears to be several micrometers to nanometers in thickness.

In this work, the electrochemically polymerized, highly conductive PANI polymerized on the sheet-like structure of MoSe₂. The surface morphologies of the as-prepared composite materials were examined using FE-SEM and HR-TEM image analysis, in which they appear to have polymer-covered sheet-like structures. Furthermore, the XRD pattern of the electropolymerized PANI@2D MoSe₂ exhibited an octahedral structure. The FT-IR spectral analysis of the as-prepared composite consists of cyano groups connected to molybdenum hydroxide in the regions of 1645 cm⁻¹ and 3450 cm⁻¹. Additionally, EIS studies found that a better electrical conductivity of 4.56 × 10⁻³ S/cm was achieved at room temperature. The DSSCs were assembled with pristine PANI, 2D MoSe₂, PANI@2D MoSe₂, and Pt counter electrodes. Finally, compared to high-performance CEs, the electropolymerized PANI@2D MoSe₂ composite CE results in 8.13% efficiency.

2. Materials and Methods

2.1. Materials

Fluorine-doped tin oxide (FTO) coated on glass plates (TEC7) (specifications: dimension: 1″ × 1″ × 2.2 mm, nominal FTO film thickness: 250 nm), acetone, isopropanol, titanium dioxide, aniline monomer, hydrochloric acid (HCl), platinum paste, selenide powder, and ethanol were purchased from the Sigma-Aldrich chemical company, India Pvt. Ltd. (Safdarjung Enclave, New Delhi, India). PEO, acetonitrile, iodine, potassium iodide, and HMImI ionic liquid were obtained from Alfa Aesar. An N719 dye sensitizer was purchased from solaronix chemical company in Switzerland. All chemicals and materials utilized in the synthesis and characterization of the composites were of analytical grade and used without further purification.

2.2. Hydrothermal Synthesis of Flower-like Two-Dimensional Molybdenum Selenide (2D MoSe₂)

Two-dimensional molybdenum selenide (2D-MoSe₂) sheets were prepared using the hydrothermal method. First, 0.1 M of sodium molybdate, 0.1 M of selenide powder, and 0.1 M of citric acid were dispersed in 80 mL of deionized (DI) water for 30 min. The solutions were stirred for 4 h. Then, the above-mixed solutions were transferred into a 100 mL autoclave (Teflon-linked stainless steel). The reaction containing the Teflon-linked stainless steel was maintained at a temperature of 210 °C for 24 h. After 24 h, the reaction vessel cooled naturally. Then, the product solutions were washed with water and ethanol (centrifuged) several times. Finally, the precipitate was left to settle in the bottom of the centrifugation tube and then dried in a vacuum oven at 80 °C overnight. The dried, collected powder product was assessed and the two-dimensional sheet-like structure of 2D MoSe₂ was obtained. The preparation and schematic diagram detailing the hydrothermal synthesis of the 2D MoSe₂ counter electrode is presented in Figure 1.

2.3. Electrochemical Synthesis of Polyaniline and Two-Dimensional Molybdenum Selenide (PANI@2D MoSe₂) Counter Electrode

The composite of PANI@2D MoSe₂ was synthesized using the electrochemical polymerization method. Typically, 0.3 gm of MoSe₂ is well dispersed in 50 mL of 01.M of HCl electrolyte solutions. The counter electrode (CE) is usually platinum (Pt), and the reference electrode (RE) is Hg/Hg₂Cl₂. Aniline monomer is dissolved in 0.1 molar of hydrochloric acidic electrolyte solution. The monomer concentration typically ranges from 0.1 M to ensure uniform polymerization. The scheme of the electrochemical synthesis of the PANI@2D MoSe₂ composite counter electrode is shown in Figure 1.

2.4. Electropolymerization Parameters

The process was performed using cyclic voltammetry (CV), with the potential swept between −1.0 and 2.0 V at a scan rate of 50 mV/S for 10 cycles. A current density of 0.1–2.0 mA/cm² was applied for controlled polymerization growth.

2.5. Device Fabrication

As-prepared PANI@2D MoSe₂ was coated on an FTO plate using the doctor blade technique. Before the coating process, TiO₂ NPs were soaked in 0.5 mM of ethanol containing N719 dye used as a photo-anode. In addition, 0.5 M of PEO and KI/I₂ redox couples was used as the electrolyte medium. Then, 2D MoSe₂, PANI, PANI@2D MoSe₂, and Pt were coated on FTO plates and used as the CEs for the DSSC. The sandwich-type DSSC was assembled with N719 dye-sensitized TiO₂ as the photo-anode and the PANI@2D MoSe₂-coated FTO plate as the CE. The PEO containing KI/I₂ redox couples was injected into the cell. Similar methods were used to fabricate DSSC devices with pristine 2D MoSe₂, PANI, and Pt CEs.

2.6. Characterization

From FE-SEM and HR-TEM images, the surface morphology of 2D MoSe₂, PANI, and PANI@2D MoSe₂ was analyzed using an FEG Quanta 250 from the Czech Republic and an FEI Technai G2 F30 (FEI Company, Eindhoven, The Netherland) at magnifications ranging from 58× to 1× and an operating potential of 300 kV. The crystalline structure of PANI@2D MoSe₂ was examined using an X-ray diffraction model ‘X’pert pro-PAN analytical diffractometer with Cu Kα radiation at 40 kV/30 mA. The functional groups of PANI@2D MoSe₂ were identified via FT-IR spectral analysis, with spectra recorded using a Jasco 4600 (PS400, Jasco, Heckmondwike, UK) in the wavenumber range of 4000 cm⁻¹ to 400 cm⁻¹. The I–V performance of the dye-sensitized solar cell was measured using a solar simulator (Model 69907, Oriel, Newport, Irvine, CA, USA) and a Keithley source meter (2420) under AM1.5G illumination. A mask with a window of 0.15 cm² was clipped onto the counter electrode side to define the active area of the cells.

3. Results and Discussion

3.1. Electrochemical Synthesis of PANI@2D-MoSe₂ Composite

During the electrochemical polymerization, characteristic peaks were observed in the voltammogram corresponding to the different redox states of the PANI@2D-MoSe₂ composite. Figure 2a,b corresponded to CV curves of the PANI and PANI@2D MoSe₂ composites. An anodic peak appeared at 0.3 V vs. Ag/AgCl, corresponding to the transition from the leucoemeraldine base (fully reduced form) to emeraldine salt (partially oxidized form). Another anodic peak was observed at 0.8 V vs. Ag/AgCl, indicating the transition from emeraldine salt to pernigraniline (fully oxidized form) [16].

The cathodic peaks in the range of −0.2 V to 0.6 V vs. Ag/AgCl were associated with the reduction of the emeraldine salt back to leucoemeraldine base and the reduction from pernigraniline to emeraldine salt.

Electropolymerization steps:

Oxidation of aniline monomers:

C₆H₅NH₂ → C₆H₅NH₂⁺ + e⁻

The aniline monomers are oxidized at the electrode surface, forming radical cations.

Dimerization of aniline radical cations:

2C₆H₅NH₂⁺ → (C₆H₄NH₂)₂ + 2H⁺

The radical cations couple to form dimers, which further react to form long oligomers and, eventually, PANI chains.

Growth of PANI chains:

(C₆H₄NH₂)_n + n e⁻ → (C₆H₄NH₂)_n (PANI chains)

The PANI chains grow as the electropolymerization continues, forming a film on the MoSe₂-coated FTO surface.

Electrochemical polymerization offers several advantages over solvothermal and chemical methods for synthesizing PANI@MoSe₂. This technique enables the precise control of film thickness, morphology, and doping levels by adjusting the applied potential and deposition parameters. The approach encourages uniform polymer growth on MoSe₂, which improves interfacial adhesion and facilitates charge transfer. Additionally, electrochemical polymerization occurs under mild conditions, eliminating the need for the harsh chemicals and high temperatures commonly required by other methods. This results in a highly conductive and defect-free polymer network, enhancing overall electrochemical performance. The method’s simplicity, reproducibility, and environmental friendliness make it an ideal choice for producing efficient PANI@MoSe₂ composites for DSSCs.

3.2. FE-SEM Image Analysis

Field-emission–scanning electron microscopy (FE-SEM) was used to analyze the surface morphologies of PANI, 2D-MoSe₂, and PANI@2D-MoSe₂. In the FE-SEM image analysis, the PANI surface morphology appeared in a nanofiber-like structure. The FE-SEM image of the PANI is depicted in Figure 3a. The 2D MoSe₂ surface appears as a sheet-like structure in Figure 3b. An FE-SEM image of PANI@2D MoSe₂ is shown in Figure 3c. The surface morphology of PANI@2D MoSe₂ was observed in the PANI polymer covering a 2D MoSe₂ sheet, and was also observed on uniform, smooth surfaces because the positive charge of the PANI polymer covalently connected to the negative charge of the molybdenum selenide [17]. The higher surface area of most of the surface edges of 2D MoSe₂ resulted in the uniform deposition of PANI on the FTO plate. These combinations also led to better surface smoothness compared to PANI and 2D MoSe₂. The FE-SEM imaging provided high-resolution morphological insights into the PANI@2D-MoSe₂ composite, revealing its uniform distribution and nanoscale features. This helped in understanding the surface roughness, porosity, and interfacial interactions, which are crucial for enhancing charge transfer and catalytic activity in DSSCs.

3.3. HR-TEM Image Analysis

High-resolution transmission electron microscopy (HR-TEM) was used to explain the internal surface phenomenon of the PANI, 2D-MoSe₂, and PANI@2D-MoSe₂ composite counter electrodes. Figure 4a–c show the HR-TEM images of PANI, 2D MoSe₂, and PANI@2D MoSe₂. The surface morphology of PANI was found to have a nanofiber structure, as seen in Figure 4a. The 2D MoSe₂ surface morphology appears as a sheet-like structure, as shown in Figure 4b. The electropolymerized PANI@2D MoSe₂ surface morphologies were found to have a sheet-like structure. Here, the polymer was uniformly deposited on the 2D MoSe₂. Due to polymers being deposited on the more active edges and the better surface active area of the metal selenides, these composites improve the crystalline growth and crystalline nature of the working electrode surface. An HR-TEM image of the electropolymerized PANI@2D MoSe₂ is shown in Figure 4c [18]. The selected area electron diffraction (SAED) pattern of the as-prepared composite was observed in the hexagonal crystalline structure, as shown in Figure 4d. The octahedral crystalline structure of the PANI@2D-MoSe2 composite plays a crucial role in boosting its electrical conductivity, making it a strong candidate for use as a counter electrode in energy applications. The 2H-phase MoSe2, known for its octahedral coordination, exhibits metallic-like behavior due to the overlap of Mo-4d orbitals, which facilitates efficient charge transport. The addition of polyaniline (PANI) further enhances conductivity through π-π interactions and polaronic conduction, resulting in a synergistic effect between the two materials.

The composite’s layered design offers a significant surface area, increasing the number of active sites for charge transfer, which, in turn, lowers interfacial resistance and improves electron mobility. Additionally, the creation of a heterostructure enhances ion diffusion, making the composite particularly effective as a counter electrode in DSSCs. The combination of MoSe₂ metallic conductivity and PANI’s redox-active properties results in exceptional electrocatalytic activity, reduced charge transfer resistance (Rct), and improved overall performance in energy storage and conversion systems. Finally, HR-TEM imaging offers atomic-scale resolution, enabling the visualization of the lattice fringes and crystallinity of the PANI@2D-MoSe₂ composite. This helps confirm the intimate interaction between PANI and MoSe₂, which is essential for efficient charge transfer and electrocatalytic performance in DSSCs.

3.4. XRD Pattern Analysis

X-ray diffraction (XRD) pattern analysis was used to determine the crystalline nature of the PANI, 2D-MoSe₂, and PANI@2D-MoSe₂ composite. Figure 5a–c correspond to the XRD pattern of PANI, 2D MoSe₂, and PANI@2D MoSe₂. The XRD pattern of PANI (Figure 5b) appeared to be semi-crystalline in nature, with crystalline peaks observed at 2θ = 15.27°, 2θ = 18.87°, 2θ = 25.32°, and 2θ = 26.42°. These peaks also correlated to the crystalline planes of (010), (110), (002), and (100). The predominant peak at 2θ = 25.32° and the crystalline peak at (200) were associated with hydrogen bonds between polymer chains. The XRD pattern of 2D MoSe₂ is shown in Figure 5b. Peaks appeared at 2θ = 14.60°, 32.75°, 35.87°, 39.59°, 44.14°, 44.75°, 49.75°, 58.36°, and 60.39°, corresponding to the 2D MoSe₂, and crystalline planes were also observed at (002), (101), (110), (001), (003), (100), (111), and (006). The 2D MoSe₂ XRD patterns exhibited octahedral structures. The peaks observed at 2θ = 14.03°, 25.39°, 28.72°, 32.49°, 39.38°, 43.77°, 49.60°, 58.13°, and 60.28° corresponded to the PANI@2D-MoSe₂ composite, with crystalline planes also observed at (002), (200), (010), (101), (001), (003), (100), (111), and (006). Based on the XRD results, the polyaniline polymer was completely deposited on the MoSe₂ sheets. The 2θ = 14.03°, 39.38°, and 60.28° peaks correspond to the 1-T phase of 2D MoSe₂ in these XRD patterns, and the crystalline plane also appeared at (002), (101), (111), (103), (003), and (100). Figure 5c shows the XRD pattern for PANI@2D-MoSe₂ [19,20]. During the electrochemical polymerization processes, the PANI polymer was completely inserted into the sheet-like structure of the two-dimensional MoSe₂. After the insertion of polyaniline polymer into the molybdenum selenide, the semiconducting nature of the composites was reduced. The metallic nature of the octahedral phase was further increased and the crystalline nature of the as-prepared composites of PANI@2D-MoSe₂ improved. The PANI and 2D MoSe₂ were stacked with weak Van der Waals interactions between them.

The degree of crystallinity of PANI@2D-MoSe₂ was calculated using Equation (1).

$$\mathrm{C}\mathrm{r}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{l}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{y}={\displaystyle \frac{\mathrm{A}\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{o}\mathrm{f}\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{c}\mathrm{r}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{l}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{p}\mathrm{e}\mathrm{a}\mathrm{k}\mathrm{s}}{\mathrm{A}\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{o}\mathrm{f}\mathrm{a}\mathrm{l}\mathrm{l}\mathrm{p}\mathrm{e}\mathrm{a}\mathrm{k}\mathrm{s} (\mathrm{C}\mathrm{r}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{l}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}+\mathrm{A}\mathrm{m}\mathrm{o}\mathrm{r}\mathrm{p}\mathrm{h}\mathrm{o}\mathrm{u}\mathrm{s})}}\times 100$$

(1)

The degrees of crystallinity of PANI, 2D-MoSe₂, and PANI@2D-MoSe₂ composite were 18.03%, 48.23%, and 62.04%.

We investigated whether PANI exists in a semi-crystalline state within the composite. The weak diffraction peaks in XRD typically indicate a more amorphous nature. The crystallinity affects charge transport: higher crystallinity can enhance carrier mobility, while amorphous regions may introduce charge-trapping sites. The XRD analysis identified the crystalline phases of the PANI@2D-MoSe₂ composite, confirming structural integrity and phase purity. It also provided insights into interlayer spacing and crystallite size, which influence charge transport and catalytic activity in DSSCs.

3.5. FT-IR Spectral Analysis

Fourier-transform infrared spectroscopy (FT-IR) is used to identify the presence of functional groups of the PANI, 2D-MoSe₂, and PANI@2D-MoSe₂ composite. The FT-IR spectra of the electropolymerized PANI are shown in Figure 6a. The peaks appeared at 3379, 2925, 1737, 1584, 1312, 1117, 769, and 540 cm⁻¹, corresponding to the stretching vibrations of –NH₂ and –CH₃ groups, and the stretching vibrations of C=O, C-N, and -OH.

Figure 6b shows the FT-IR spectra of 2D MoSe₂, with peaks at 3374, 2913, 2359, 1638, 1092, 711, and 516 cm⁻¹, ascribed to the stretching vibrations of -OH, -CH₃, C=O, C-O/OH groups, and metal selenide ions. The FT-IR spectra of PANI@2D MoSe₂ are shown in Figure 6c. The peaks appeared at 510, 708, 1115, 1483, 1672, 2918, and 3371 cm⁻¹, associated with the stretching vibrations of selenide ions, -NH₂, C-N, -CH₃, and –OH groups [21]. The peaks at 1672 cm⁻¹ and 3371 cm⁻¹ correspond to the stretching vibrations of cyano groups attached to molybdenum hydroxide. The peak at 3371 cm⁻¹ in the FT-IR spectrum of the PANI@2D-MoSe₂ composite, attributed to cyano groups attached to molybdenum hydroxide, can influence charge transfer in DSSCs. Cyano groups introduce localized electronic states that may enhance charge carrier mobility by facilitating electron delocalization and reducing recombination losses. Additionally, their interaction with molybdenum hydroxide can modulate the electronic structure of MoSe₂, potentially improving its catalytic activity and interfacial charge transfer. This modification could contribute to the overall efficiency of the DSSC by optimizing electron transport dynamics. In addition, FT-IR spectroscopy confirms the functional groups in the PANI@2D-MoSe₂ composite, ensuring successful polymerization and interaction between PANI and MoSe₂. It also provides insights into chemical bonding, which influences charge transfer and electrochemical performance in DSSCs.

3.6. Electrochemical Impedance Spectroscopy (EIS) Studies

The electrical conductivity of the as-prepared PANI, 2D-MoSe₂, and PANI@2D-MoSe₂ composites were determined using electrochemical impedance spectroscopy (EIS) studies. EIS studies were used to determine the electrical conductivity of PANI, 2D MoSe₂, and PANI@2D MoSe₂ composite CEs. Figure 7a illustrates the EIS spectrum of electropolymerized PANI, showing the higher semicircle portion. This kind of semicircle portion indicates lower electrical conductivity. Figure 7b shows the EIS spectrum of 2D MoSe₂, with Nyquist plots showing the higher semicircle portions. Figure 7c shows the EIS spectrum of the PANI@2D MoSe₂ CE, which exhibits a lower semicircle portion and lower-frequency regions.

The lower semicircle portion and lower-frequency regions of the CE indicate lower charge transfer resistance, which results in higher electrical conductivity. Therefore, the as-prepared PANI@2D MoSe₂ composite CE shows a lower semicircle portion, indicating lower charge transfer resistance and higher electrical conductivity compared to pristine 2D MoSe₂, PANI, and Pt. This is due to the PANI NFs being covered on the 2D MoSe₂ sheets. The Pt CE-based DSSCs and their EIS curves are shown in Figure 7d, also exhibiting a higher-frequency region, higher semicircle portion, and lower electrical conductivity compared to PANI@2D MoSe₂. This composite has more surface active edges, uniform deposition of PANI on 2D MoSe₂ sheets, and better adhesion between the CE and electrolyte interface. The PANI@2D MoSe₂ composite counter electrode exhibited better electrical conductivity [12,22]. EIS studies revealed that the PANI@2D-MoSe₂ composite exhibits superior electrical conductivity compared to PANI and 2D-MoSe₂. In the Nyquist plot, the semicircle in the high-frequency region represents the charge transfer resistance (R_ct) at the electrode/electrolyte interface. A smaller semicircle indicates lower Rct, signifying faster charge transfer and enhanced conductivity. The PANI@2D-MoSe₂ composite shows the smallest semicircle, with an Rct value of 3.14 ohm cm², confirming its excellent charge transport properties. This can be attributed to the uniform deposition of polyaniline on two-dimensional MoSe₂ sheets, which enhances electron mobility, increases surface area, and improves electrocatalytic activity for efficient redox reactions. EIS analysis evaluates the charge transfer resistance and conductivity of the PANI@2D-MoSe₂ composite, helping to understand its electrochemical performance. A lower charge transfer resistance indicates efficient electron transport, enhancing DSSC efficiency.

3.7. I–V Characterization

The I–V characterization curves of the PANI, 2D MoSe₂, PANI@2D MoSe₂, and Pt CEs are presented in Figure 8a–d and the measurement values are listed in

Table 1. I–V curve values of the as-prepared PANI, 2D-MoSe₂, PANI@2D-MoSe₂ composite, and Pt CEs for the DSSC.

Counter Electrode	Jsc (mA cm−2)	Voc (V)	FF (%)	Ƞ (%)
PANI	15.45	0.73	0.45	5.07
2D-MoSe2	16.09	0.77	0.47	5.82
PANI@2D-MoSe2	17.33	0.82	0.52	7.38
Pt	16.75	0.79	0.50	6.61

. The efficiency of the solar cell devices was calculated using the following formulae:

FF = (J_max × V_max)/(J_sc × V_oc)

(2)

ƞ (%) = (J_sc × V_oc × FF)/P_in × 100

(3)

Here, J_max is the maximum current output, V_max is the maximum voltage output, J_sc is the short-circuiting current density, V_oc is the open circuit voltage, FF is the fill factor, and η is the efficiency.

The I–V curves of the PANI NF and 2D MoSe₂ sheet CEs are presented in Figure 8a,b. The DSSC device fabricated with the PANI NF CE achieved 5.07% efficiency, while the 2D MoSe₂ sheet CE achieved an efficiency of 5.82%. The DSSC device using the Pt CE achieved an efficiency of 6.61%. The PANI@2D MoSe₂ CE achieved a higher efficiency of 7.38% due to the higher electrical conductivity of the PANI covering the metallic nature of the octahedral phase of the 2D MoSe₂. The carbon-based materials of the PANI combined TMCs, further improving the surface active area of CE and providing better interfacial contact between the CE and electrolyte interface, faster regeneration of iodide/tri-iodide redox couple, and reducing the recombination rates of the CE. The increasing current and potential of the device increased the fill factor of the device. Increasing the fill factor of the device always increases the efficiency of the device. The I–V curves of the PANI@2D MoSe₂ and Pt CEs are presented in Figure 8c,d [23,24].

The WO₃@PANI composite achieved an efficiency of 6.78% with a charge transfer resistance (R_ct) of 10 ohm cm² [19]. The poly(pyrrole) (PPy) polymer attached to the strontium titanate (PPy-SrTiO₃) composite counter electrode exhibited a lower efficiency of 2.52% and a higher R_ct value of 46.4 ohm cm² [25]. The nickel–polyaniline–graphene-based composite counter electrode demonstrated an efficiency of 5.80% with an R_ct of 10.78 ohm cm² [26]. Similarly, the PANI-3% cobalt sulfide composite counter electrode achieved an efficiency of 6.14% with an R_ct value of 12.02 ohm cm² [27]. Among these, the as-prepared PANI@2D-MoSe₂ composite exhibited the highest efficiency of 7.38% and the lowest Rct value of 3.14 ohm cm². The superior performance of the electropolymerized PANI@2D-MoSe₂ composite can be attributed to the uniform deposition of polyaniline on the two-dimensional molybdenum selenide sheets. This sheet-like structure offers a higher surface area, improved electrical conductivity, and enhanced electrocatalytic activity due to the presence of selenide materials. Additionally, it facilitates the rapid regeneration of the iodide/tri-iodide redox couple, contributing to its enhanced efficiency.

Finally, the improved efficiency of 7.38% in DSSCs with the PANI@2D-MoSe₂ composite can be attributed to several key factors. The strong interfacial interaction between PANI and MoSe₂ facilitates efficient charge transfer, reducing recombination losses. The 2D morphology of MoSe₂ provides a large surface area, enhancing dye adsorption and electron transport. Additionally, PANI contributes to superior conductivity and catalytic activity, improving redox reactions at the counter electrode. The synergistic effect between these components enhances charge separation and transport dynamics, ultimately boosting the device’s performance. I–V characterization measures the photovoltaic performance of the PANI@2D-MoSe₂ composite, providing key parameters like efficiency, fill factor, and current density. It helps assess the composite’s effectiveness in enhancing charge transfer and overall DSSC performance.

4. Conclusions

In conclusion, the PANI@2D MoSe₂ composite was successfully prepared using the electrochemical polymerization method. The surface morphology microstructure FE-SEM image analysis revealed the polymer-covered sheet-like structure of the PANI@2D MoSe₂. The HR-TEM nanostructure surface image study also observed 2D MoSe₂ sheet-like composites in the PANI. The X-ray diffraction pattern results confirmed electropolymerized PANI@2D MoSe₂ in the octahedral phase. FT-IR spectroscopy analysis confirmed that the PANI containing the cyano groups was attached to molybdenum hydroxide at the regions of 1672 cm⁻¹ and 3371 cm⁻¹. In addition, EIS studies demonstrated that the composite CE exhibited the highest electrical conductivity of 3.47 × 10⁻⁴ S/cm. Finally, the electropolymerized PANI@2D MoSe₂ composite CE achieved 7.38% efficiency. The electropolymerization of PANI@2D-MoSe₂ ensures the precise control over film thickness, uniformity, and doping levels, enhancing conductivity and charge transfer. Unlike chemical or solvothermal methods, electropolymerization occurs under mild conditions, avoiding harsh reagents and high temperatures. This method improves interfacial adhesion, structural integrity, and electrocatalytic activity, making it ideal for DSSC applications.