All electrochemical experiments were carried out using either a conventional three-electrode cell or a previously described electrochemical cell [15] . A BAS 100W electrochemical analyzer (Bioanalytical Co.) was used to perform the electrochemical studies such as cyclic voltammetry (CV) and chronoamperometry (CA). Steady-state reflectance spectra were performed using Shimadzu UV-2101 PC. Irradiations were performed with a solar simulator 300-watt xenon lamp with an IR filter (Newport). Electrochemical Impedance spectroscopy (EIS) was carried out using a Solarton 2101A. Photoelectrochemical (PEC) studies of the thin solid films in gel electrolyte were performed using 2.0 cm² fluorine-doped Tin Oxide (FTO) covered with the photoactive material as a working electrode, and platinized FTO (Pt-FTO) served as both reference and counter electrode. Unless otherwise stated, all potentials were measured against platinized FTO (0.597 vs. SHE).

A CV in situ technique was used to incorporate SiC or CN nanoparticles, as well as a mixture of both, into PTF. In a typical 2-electrode cell setup, FTO serves as the working electrode, while Pt-FTO functions as both the reference and counter electrode. Subsequent sections will provide more details about the in-situ formation of CN/SiC/PTF.

Thermoplastic gel electrolyte (TPGE) was prepared following the published procedure [16] . Briefly, 0.65 M KI and 0.065M I₂ were dissolved in 10 mL polycarbonate (PC), and then 8.5 g of PEG (M-20000) was added to the mixture. The mixture was heated at 100˚C under continuous stirring for ca. 12 h in a flask under an inert atmosphere. The mixture was hydrothermally treated at 180˚C for 14 h in a Teflon autoclave.

A 100 µL of 10 mM monomer solution with or without the SiC or CN was placed onto a rectangular conducting fluorinated Tin oxide glass (FTO) window area of 1.5 cm² working electrode. The monomer spread evenly on the electrode surface and further evaporated the solvent. A 200 µL of 1:10 I₂/KI in polyethylene glycol gel electrolyte was placed on the top of the monomer layer. Immediately the counter electrode was placed on top of the gel electrolyte and pressed to allow an even spread of the electrolyte between the two electrodes.

The following steps were performed to report the in-situ PEC responses of studied assemblies.

Prepare the EC cell as mentioned in the experimental section.

Charge involvement for monomer-dark (Q_M-D), monomer-light (Q_M-L), and polymer light (Q_P-L) was calculated by integrating the area of each resultant voltammogram.

“Photocurrent and the resulting photo-generated charges are used to measure photoactivity”. Therefore:

- (Q_M-L) − (Q_M-D) = Charge activity of the monomer or (PEC-M)

- (Q_P-L) − (Q_M-D) = Charge activity of the polymer or (PEC-P)

- Q Photo charge due to polymerization = (PEC-P) − (PEC-M).

The light absorption of the assembly consisting of PTF/SiC-CN has been examined. The results are presented in Figure 1 and Figure 2. Figure 1 illustrates the similarities in the absorption pattern of SiC (band gap 2.31 eV) and CN (band gap 2.48 eV). Previous studies [17] have indicated that the spectra of the mixed SiC and CN show a broadening of the light absorption range, suggesting an interaction between the SiC and CN as an active mixture. Figure 2 shows Tauc plots used to analyze the absorption data presented in Figure 1 . Figure 2(A) suggests that a direct band gap likely exists. The multiple absorption peaks seen in Figure 1(B) result from the potential coexistence of various forms of SiC and CN. It should be noted that the absorption edge at 2.3 eV ( Figure 2(B1) ) is for PTF. The presence of multi-absorption peaks for PTF is due to insoluble oligomers within the polymer matrix of PTF. These oligomers absorb higher energy photons.

Figure 1 and Figure 2 indicate that all components of the assembly PTF/SiC-CN absorb visible light photons. This promotes the additive absorption action which effectively absorbs most of the visible light photons posing energy between 3.1 to 2.1 eV. The multiple absorption peaks for the prepared assemblies indicate the possible formation of hybrid sub-bands. The absorption spectra of the SiC/CN mixture and that of SiC/CN occluded in PTF are displayed in Figure 3(A) & Figure 3(B) respectively. This figure shows a noticeable shift of absorption edges and peaks of the SiC/CN ( Figure 3(A) trace 1) from that of SiC/CN /PTF ( Figure 3(A) trace 2). The addition of PTF causes an increase in absorption at a longer wavelength (red shift). Comparing the absorption profile of each component alone ( Figure 2 ) and that of the mixed components ( Figure 3 ) shows a similar pattern, however, the absorption spectra of the mixture have the potential of effective absorption of more visible light.

The PEC studies were conducted on FTO/SiC, FTO/CN, FTO/SiC-CN, and FTO/SiC-CN-PTF in the thermoplastic I⁻/ $I_3^{-}$ gel electrolyte (TPGE). The studies were conducted in the dark and under illumination, with a scan rate of 0.10 V/s. Some of the CVs are shown in Figures 4-6 , while the complete results are listed in Table 1 and Table 2 . In-situ monomer/polymer transition studies are performed when TF is involved in any process.

$R={\text{e}}^{-\frac{t}{\tau }}$

where t is time, τ is the transient time constant, and $R=\left(I_t-I_{st}\right)/\left(I_{in}-I_{st}\right)$, as I_t is current at time t, I_in is immediate photocurrent, and I_st is the stationary value of photocurrent (steady current). The plot of ln R vs. time ( Figure 5(B) ) generates a straight line with slope = 1/τ. The reciprocal of the slope determines the value of τ, in seconds. The calculated τ is ≈ 5.49 seconds.

The CV scan for the FTO/SiC-CN was not identical but like that shown in Figure 4 . However, the magnitude of photocurrent was less than that recorded in the presence of PTF. The study was focused on the potential range between 0 to −1.6 V. Figure 6(A) displays a CV scan for the SiC/CN in gel electrolyte under dark and illumination. The figure shows that upon lighting, there is an increase in the recorded current in both cathodic and anodic scans. It can be noticed that the photocurrent starts to exceed the recorded current (In the dark) at ≈ −0.2 V vs the reference electrode. This shifts the fermi level (E_flat-band) at 5.0 eV. This is a shred of evidence that adding PTF alters the energy map structure of the assembly

FTO/SiC/CN. Figure 6(B) displays chronoamperometric studies at −1.2 V for SiC/CN under dark and under illumination. Again, the phenomena of dark currents show up as indicated by the shaded area in Figure 6(B) . The calculated transient time constant τ is ≈ 100 s ( Figure 6(C) ). This is much longer than that calculated in the presence of PTF (≈5.49 s). This indicates that PTF creates effective interfaces that facilitate charge carrier movements.

Following the protocol described in section 2.5, the obtained CV scans were like that displayed in Figure 7 . The outcome of these calculations is listed in Table 1 .

a: SiC, or C₃N₄ or both.

Upon detailed analysis of the data shown in Table 1 , the following findings are noticed:

1) The presence of PTF with CN, SiC, and both enhances the photocurrent outcome (approximately 5^th column).

2) PTF with a mixture of SiC and CN gives the highest photocurrent (approximately in the 6^th column).

3) TF with SiC exhibits a slightly higher increase in the photo response compared to CN.

These findings support the assumption that PTF creates effective interfaces with both SiC and CN that facilitate charge carrier movements. This resulted in a better photo response outcome.

Certain photodiode characteristics such as responsivity (R) can be calculated from the ratio of photocurrent and the optical power density of incident light, Detectivity (D) is a measure of the ability of a photodetector to distinguish weak signals from noise, Ideality factor (n) indicates how a diode's current-voltage characteristics closely match an ideal diode, Barrier height (Ф) is the energy barrier at the p-n junction that electrons have to overcome to go through the diode, S (sensitivity of the diode to light) is the ratio of photocurrent to dark current at a given voltage, indicating the ability of the diode to conduct current in one direction compared to the other. The photodiode parameters of the studied photo assemblies FTO/SiC-CN, and FTO/SiC-CN /PTF were determined following the previous work [19] and listed in Table 2 .

The calculated R, D, and n values for the studied assemblies were closer to that previously calculated [19] for organic photodiodes.

EIS of the FTO/SiC/CN/PTF assembly in gel electrolyte was achieved between 10⁵ and 10⁻¹ Hz different potentials. Nyquist plot and log σ AC conductivity vs Log frequency generated from this study in the dark and under illumination, are displayed in Figure 8 and Figure 9 . Figure 8 shows mainly diffusional control across the studied frequency range. Figure 8(A) indicates that light decreases the film resistance at high frequency as shown from the intercept with the real Z axis. On the other hand, Figure 8(B) shows a kinetic control at high frequency. The illumination does not affect film resistance at high frequencies. At low frequencies the diffusional control is shown under both dark and illumination, however, illumination increases the imaginary impedance. No evidence of charge saturation is reported. The shape of the Nyquist plot with the presence of an un-concentered semicircle at high frequencies and Warburg impedance at low frequencies ( Figure 8(B) ) reflects film porosity [20] .

The plot in Figure 9 shows the relationship between the conductivity (σ) and frequency (ω) for FTO/SiC/CN/PTF in gel electrolyte. The AC conductivity increases with frequency up to approximately 130 Hz. After this point starts to decrease regardless of the applied potential. This is contrary to what was reported previously with FTO/SiC/PTF [21] . The decrease of AC conductivity at frequencies greater than 100 HZ, can be attributed to the presence of CN with SiC occluded in PTF. In assembly FTO/SiC/PTF such behavior was not observed. This suggests that CN, at higher frequencies, affected the mobility of the charge carriers in the applied electric field, resulting in reduced net movement of charge and lower conductivity. Under illumination, no tangible changes in the conductivity compared to that measured in the absence of light. However, at the low-frequency range (ca 0.01 - 10 Hz), the AC conductivity measured at 0.0 ( Figure 9(A) ) was less than that measured at −1.0 V ( Figure 9(B) ). This can be explained based on increasing charge carriers at −1.0 V due to the polarization of gel electrolyte’s ions at this applied potential.