TiO2-ZnO rodlike nanocomposite as photoanode in DSSC yielding 7.38% PEC with N3 dye

doi:10.21203/rs.3.rs-4929667/v1

Download PDF

Research Article

TiO2-ZnO rodlike nanocomposite as photoanode in DSSC yielding 7.38% PEC with N3 dye

https://doi.org/10.21203/rs.3.rs-4929667/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

The agglomeration of TiO₂-ZnO nanocomposite is a well-established strategy to apprehend various energy photons from the solar spectrum. This research article focuses on direct chemical precipitation protocol for rod-like TiO₂-ZnO NPs of different TiO₂:ZnO molar ratios for solar energy harvesting using N3 dye. The synthesized nanocomposites were evidenced with various analytical probing techniques. X-ray diffraction scrutiny corroborated rutile and hexagonal wurtzite crystal structure for TiO₂ and ZnO respectively. Surface morphology depicted nanorod texture with varying diameters and widths whereas elemental analysis studies confirmed optimal stoichiometry for the presence of Ti, O, and Zn, respectively. The optical energy gap was evaluated using UV-visible spectroscopy was between 2.95 to 3.00 eV. A 2D electron diffraction pattern was captured with the SAED technique to reveal nanocrystalline TiO₂-ZnO nanocomposite. Among the samples synthesized, composite having TiO₂:ZnO having 3:1 ratio showcased good performance in solar energy conversion registering Jsc = 3.25 mA/cm², Voc = 946.96 mV, FF of 48% with PEC of 7.38% in an unadulterated aqueous 0.1 M I⁻/ I₃⁻ electrolyte under 100 mW/cm² irradiation while EIS investigation resulted in Rs = 3.17 cm², Rct = 20.14 cm², Cdl (10^-9) = 40.25 F/cm² and Zw (10^-5) = 3.27 mMho.

Direct chemical precipitation

photo-conversion efficiency

DSSCs

X-ray photoelectron spectroscopy

Global energy consumption is expected to continue growing and reach approximately 23 terawatts (TW) in 2050. Currently, 80% of the world's energy demands are met by burning fossil fuels, which have a major negative impact on the environment. Concerns like energy consumption, global warming, and the depletion of fossil resources can all be addressed by developing green energy alternatives. The well-known DSSCs show potential as a silicon-based solar cell alternative to meet the world's expanding energy needs. The performance of modern DSSCs is now more competitive because to advancements in high-efficiency dye sensitizers, durable electrolytes, and nanostructure semiconductors. A breakthrough in developing innovative solar cells that can gain traction in the DSSCs market will be achieved through candid processing, inexpensive materials, and a wide range of applications. With peak power conversion efficiencies (PCEs) of about 14.7%, dye-sensitized solar cells (DSSCs) have come a long way in the two decades since O'Regan and Grätzel's seminal work on the subject in 1991. In this work, we have examined hybrid approaches to enhance the efficiency of dye-sensitized solar cells (DSSCs) by combining TiO₂/ZnO with ruthenium complex dye. Due to their wide bandgaps, semiconductors made of TiO₂ and ZnO can only absorb UV light in that range. [1–5]. Photoreaction can be enhanced by a composite that absorbs 400 nm-wavelength visible light. Reducing electron-hole recombination can also be facilitated by improving the charge separation of the composite. Because ZnO and TiO₂ have almost same energy levels, comparable band gaps, and equivalent bonding strengths, they can be mixed to produce a nanocomposite with superior physicochemical properties. [6–9].In this case, the injection process and exciton formation will be greatly impacted by the use of semiconductors made of n-type metal oxide nanocomposites. Nanocomposite materials have a number of benefits, including easier production of a variety of shapes, safety, and reduced fabrication costs. [10]. Recently, DSSCs have attracted interest because of their low cost, high conversion efficiency, and simplicity of construction. The dye and semiconductor are the focus of most performance-enhancing techniques for DSSCs, and they need to be optimized for effective light enveloping, rapid electron transport, and unattenuated electrical contact between the dye and semiconductors. [11, 12]. Due to its benefits, such as benign nature, durability against external conditions, chemical robustness in the electrolyte, ambient and cryogenic synthesis, and vast texturing of TiO₂ morphologies it is widely used as photoelectrode material [13]. However, TiO₂, a broad bandgap semiconductor, cannot absorb in the visible region. ZnO has better carrier mobility than TiO₂, however, there are several significant downsides, including dye aggregation development and instability in an acidic environment along with these factors decelerated electron injection rate in ZnO than in TiO₂ results in poor photocurrent [14]. Instead of simple TiO₂ electrode, coaxial TiO₂/ZnO nanotube arrangement showed enhanced exciton separation, reduced recombination, and results in 40% higher efficiency [15]. ZnO presence in composite positively influences the efficiency of ZnO-coated TiO₂ nanoparticles which consequentially boosted its efficiency from 0.7–1.21% which is an aftermath of minimal recombination between the electrolyte and electrode.

Titanium dioxide (TiO₂) is an active photoelectrode that has favourable environmental characteristics, an adjustable bandgap, and good optical and electrochemical qualities [16–18]. Due to lower recombination, research on TiO₂, ZnO, and double-layer TiO₂/ZnO revealed that the bilayer was more efficient than individual semiconductors [19]. Owing to the importance of the subject, these materials were created by the chemical precipitation method, annealed at 450°C, and the results were given for the current study. Additionally, the morphological and optical characteristics of TiO₂/ZnO, as well as their preparations and combination, were studied. In most cases, the dye utilised as a sensitizer in DSSCs is essential to light inclusion and the subsequent conversion of light into electricity.

[20]. The Power conversion efficiency (PCE) was increased by around 11–12% when the Ru-complexes were combined with a broad bandgap TiO₂-ZnO nanocomposite. Because of the absorption across the visible spectrum,efficient charge transfer,, prolonged excitation duration, strong metal to ligand charge transfer, and easily adjustable redox properties, transition metal complexes like Ru-complexes are the most widely available and used in solar cells. [21]. According to research, during esterification, the dye is chemically bonded to the TiO₂, causing the protons in the anchoring group to partially transform into the surface of the TiO₂. Consequently, the performance of the photovoltaic (PV) cell was influenced by the quantity of protons on the N3 photosensitizer. [22, 23]. another way, the change in the protonation level of N3 (N712, N719) dictates the device's performance in two main ways. Initially, increase in proton concentration leads to positively charged TiO₂ surface and the decreasing Fermi level of TiO₂. As a result, the surface protonation-induced positive shift of the conduction band boundary causes a decrease in the V_OC. Second, the surface dipole's electric field increases the anionic Ru(II) complexes' absorption and, as a result, forces the injection of electrons from the dye's excited state into the TiO₂ conduction band. When ruthenium dye, sometimes known as "black dye," is used in DSSCs, Nazeeruddin et al. (2001) documented efficiency of 10.4% [24]. This dye's broad absorption profile spans the whole visible spectrum. Grätzel and coworker synthesized monoprotonated sensitizer N3 [TBA]3 dye registered PCE of 9.3%, furthermore, they worked to produce a di-protonated sensitizer N3 [TBA]2 or N719, which had an 8.4% conversion efficiency [23]. Furthermore, assemblies that employed black dye as a sensitizer showed η = 10.5% [25] and 11.1% [26] by Wang et al. and Chiba et al. Ruthenium complexes are proven sensitizer with a photoconversion rate of up to 14% [27]. The performance of the DSSCs that were generated by using TiO₂, ZnO, and TiO₂/ZnO nanoparticle films was examined, and the N3 dye was employed as a sensitizer. These composites were created by a small number of groups as photoanodes for DSSCs; they had low PCE and required challenging production procedures. Using a direct precipitation method, we created these composites and employed them as photoanodes in our investigation. TiO₂-ZnO composite, with a molar ratio of 3:1, produced the maximum photo-conversion efficiency of 7.386% (AB3) under the ideal conditions.

2.1 Materials and methods

Titanium tetra-isopropoxide [C₁₂H₂₈O₄Ti] as a source of titanium and Zinc nitrate [Zn(NO₃)₂.6H₂O] for source of zinc both are of AR grade from Spectrochem. Hydrochloric acid (pH adjustment) and Ammonia were availed from Thomas Baker.

In order to produce the nanocomposite10 ml (0.3 M) of Titanium tetra isopropoxide solution, was charged in a 100 ml beaker blended with deionized water was stirred magnetically for fabrication of TiO₂-ZnO thin films. The above-mentioned solution was gradually mixed for a half-hour with addition of 10 ml (0.3 M) Zn(NO₃)₂ solution. To obtain the desired composites, several proportions of the relative amounts of the two precursors were used, as depicted in Table 1.1.

Table 1

Volume ratio for synthesis of A, AB1, AB2, AB3, and B thin films
Sr. No.	Sample Code	0.3 M TTIP (ml)	0.3M Zn(NO₃)₂ (ml)	HCl (ml)	NH₄OH (ml)
1	A	20	-	12	-
2	AB1	25	75	13	-
3	AB2	50	50	28	-
4	AB3	75	25	34	-
5	B	--	20	-	20

The obtained clear solution was placed at room temperature till we obtained a powder of TiO₂-ZnO nanocomposite. This powder was annealed for two hours at 450°C in a muffle furnace to enhance the crystal ageing of the sample. Likewise, bare TiO₂(T) and ZnO(Z) were amalgamated and annealed at 450°C for two hours.

A thin coating of the TiO₂-ZnO nanoparticles were deposited on the (FTO) glass. Initially, FTO were cleaned with isopropyl alcohol, acetone, and deionized water respectively. Employing a screen printing technique, the unmixed TiO₂, ZnO, and TiO₂-ZnO nanocomposite thin film was applied on previously cleaned FTO. To achieve DSSCs, prepared films were dipped in an aqueous 1% N₃ dye solution, which was then left to soak overnight in the dark. An N₃ dye-loaded film appears reddish-orange. Figure 1 illustrates a schematic of the method used to create dye-coated TiO₂-ZnO-based film. The ratios of 1:0, 1:3, 1:1, 3:1, and 0:1 of the TiO₂:ZnO composition have been synthesized and are referred to as A, AB1, AB2, AB3, and B respectively. The same procedure is presented in a flow chart of Fig. 1.1.

2.2 Characterization

The X-ray diffraction (XRD) (Bruker AXS-D8) technique was utilized to study structural analysis and phase identification. The elemental oxidation degree of DSSCs were scrutinized by (XPS) X-ray photoelectron spectroscopy (XPS, Thermo Scientific, Multilab-2000) bearing multichannel scanner. Scanning electron microscopy (SEM) in conjugation with (EDS) energy dispersive spectroscopy (JEOL-JSM Model-6360A) was exercised to depict the morphology and composition. The crystallinity of the nanocomposite was evidenced with (HR-TEM) High-resolution transmission electron microscopy along with (SAED) selected area electron diffraction (Philips model-Technai F20). All the sample's photoelectrochemical characteristics were measured using tungsten filament of 20 mW/cm² light intensity. The PEC cell was constructed of TiO₂, ZnO, and TiO₂-ZnO nanocomposite photoanodes, counter electrodes, and a redox pair of iodide/polyiodide. The PEC performance (I–V) was recorded on the Autolab (PGSTAT-100 Potentiostat).

3.1 UV–Visible spectroscopy of N₃ dye

cis RuL₂(NCS)₂ and ruthenium complex is a pristine example of a heterogeneous charge transfer sensitizer for DSSCs, also referred to as N₃ dye [28]. The pristine Ruthenium N3 dye is stable over a hundred million turnovers in the DSSC without any performance decline. Ruthenium N₃ dye envelopes the light from 300–800 nm. With this range of wavelength, N₃ dye is an efficacious sensitizer for wide energy gap semiconductors. Figure 1.2 displays the UV-visible spectra together with an inset of the N₃ dye's structure.

Upon coating of nanocomposite with N₃ dye a deep pink color was developed, which confirmed that the N₃ dye was adsorbed on the composite. Metal to ligand charge transfer transitions and intra-ligand transitions caused the dye to display broad, strong visible bands at 252, 313, 391, and 529 nm [29]. The carboxylate groups' function is to enable the apprehension of the sensitizer on composite surface by formation of bidentate coordination and ester linkages, simultaneously the (-NCS) groups improves absorption of visible light. As N₃ dye is excited, an electron is transferred from metal to p orbital of the surface-anchoring carboxylated bipyridyl ligand, resulting in absorption maxima at 400 nm (1.41×10⁴ M^-1 cm^-1) and 535 nm (1.45×104 M^-1 cm^-1) of metal to ligand charge transfer character.

3.2 X-ray diffraction study

The Fig. 1.3 illustrates nanocomposites diffraction patterns which were logged between 2θ = 20–80º by (XRD) X-ray diffraction technique. The prepaired films of TiO₂ (A), ZnO (B), and TiO₂-ZnO nanocomposites are coded as AB1, AB2, and AB3 respectively.

The rutile phase displays TiO₂ while the hexagonal wurtzite phase displays ZnO. The observed mixed crystalline phases are well in agreement with JCPDS data 21-1276 and 36-1451 respectively. The annealed sample of AB1, AB2, and AB3 also showed mixed considerable noticeable peaks of TiO₂, ZnO with the rutile and hexagonal wurtzite crystal structures of TiO₂ and ZnO. The composite samples support the existence of mixed phases of TiO₂ and ZnO. The prefix @ band # shows peaks of the TiO₂ and ZnO respectively in XRD. The composite, which exhibits an elevation in peak intensity of the (002) plane of ZnO with a change in composition from AB1 towards AB3, verified the synthesis of TiO₂-ZnO photoanode thin films.

Scherrer’s formula (1.1) [30] was used to evaluate the size of the crystallites in samples A, AB1, AB2, AB3, and B.

$$\:D=\frac{0.9\lambda\:}{\beta\:COS\theta\:}$$

1.1

…………………….

Where ‘D’= crystallite size,

‘λ’ = wavelength of source target (CuKα = 1.5406 Å),

‘β’= full width at half maxima, and

‘θ’= diffraction angle.

Table 1.2 displays the obtained crystallite sizes.

Table 1.2

Crystallite size of the samples A, AB1, AB2, AB3, and B
Sr. No.	Sample	Crystallite size (nm)
1	A	25
2	AB1	26
3	AB2	28
4	AB3	32
5	B	27

3.3 Morphological studies

The microstructures of the deposited thin films were examined using SEM analysis. Figure 5.4 shows the SEM pictures of TiO₂-ZnO thin films with ratios of 1:0, 1:3, 1:1, 3:1, and 0:1 respectively. Figure 1.4(a-b) reveals that agglomerated nanorod structures are formed for pure TiO₂ (A). Samples AB1 (c–d), AB2 (e–f), and AB3 (g–h) display proximate nanorod-like morphology with a range in size, in contrast. Figure 1.4 (i–j) SEM images of pure ZnO (B) revealed a tiny, agglomerated nanoparticle morphology. The sample AB3 displays an array of interconnected nanorods. The nanorods' width was roughly between 20 to 70 nm. It is instrumental for light absorption in PEC solar cells as AB3 forms an interconnected porous nanorod-like surface morphology because it offers a larger surface area for efficient light
absorption during photon irradiation.

3.4 HR-TEM

The crystal properties of the synthesized TiO₂-ZnO nanocomposite thin films are revealed by HR-TEM and SAED analysis. The HR-TEM images of the representative sample AB3 are shown in Fig. 1.5 (a–c). Figure 1.5 (b and c) depicts a collection of nanorods with an average width of 22–25 nm. The nanorod morphology was also observed in previous literature which can help increase DSSCs efficiency [31]. The upsurge of dye adsorption can be noticed for the AB3 sample with increasing particle size and its elongation. The elongated particle size of photoanodes presents a large surface area resulting in efficient dye adsorption which in turn traps more light to produce photogenerated electrons. The sizable amount of sensitizers adsorbed on the AB3 sample surface to have more electron injection from the excited state of dyes to the conduction band of AB3, the J_sc of the cell usually increases accordingly. The short-circuit current density of the cell increased with increasing particle elongation to its maximum value and then decreased. The TEM results of the AB3 sample's morphology are in good agreement with SEM and XRD data. The SAED patterns of the TiO₂-ZnO nanocomposite thin film are shown in Fig. 1.5(d). It demonstrates the development of bright spots with ring patterns that support the thin film formation as a nanocrystalline TiO₂-ZnO nanocomposite.

3.5 Compositional studies

The elemental composition of the TiO₂-ZnO nanocomposite expected stoichiometry was corroborated with EDS. Figure 1.6 (a-e) and Table 1.3 reveal EDS spectra and their associated data for the A, AB1, AB2, AB3, and B samples. The EDS verifies existence of Ti and O elements in A sample (Fig. 1.6(a)), whereas Ti, Zn, and O elements are present in the samples AB1, AB2, and AB3 in their corresponding ratios. The B sample contains Zn and O elements, as seen in Fig. 1.6 (e). The unlabelled peaks with high intensity are observed in all images of EDS they are of C atom. The carbon tape has been used in the EDS characterization of the sample therefore C shows its presence in the EDS spectra.

Table 1.3

EDS sample A, AB1, AB2, AB3, and B atomic weight percentage
Sample Name	Atomic Weight %
Sample Name	A	AB1	AB2	AB3	B
O	75.61	74.54	75.51	73.14	49.51
Ti	24.39	17.85	20.16	25.72	00
Zn	00	7.61	4.33	1.14	50.49
Total	100	100	100	100	100

3.6 UV-Visible spectroscopy

The UV-visible spectrophotometer with a wavelength scope of 190–1100 nm was utilized to evaluate the optical properties of TiO₂-ZnO thin films. Figure 1.7 depicts linear extrapolation plots ((αhν)² vs. hν) plots to deduce the optical band gap energy of the deposited films. The absorption edge from sample A to AB3 composite was slightly shifted to a longer wavelength (red shift). The optical energy gap of TiO₂-ZnO nanocomposite was calculated by extrapolating the straight line to the energy axis, as seen in the inset of Fig. 1.7 (A-B). Tauc's plot, which is presented in Eq. (1.2) [32], is used to estimate the absorption properties.

$$\:\alpha\:hv={A(hv-Eg)}^{n}$$

1.2

Here, ‘α’= absorption coefficient,

‘Eg’ = the gap energy,

‘h’ = the planks constant,

‘A’ is a parameter that depends on the probability of electron transition, and ‘n’ is the exponent for the type of electronic transition.

The absorption profile displays direct and allowed class of electronic transition hence, n = 1/2 has been taken. The calculated bandgap values for the A, AB1, AB2, AB3, and B samples were 3.1, 3.0, 2.97, 2.95, and 3.3 eV, respectively. The well-grown agglomerated and close-packed nanorods illustrated photoabsorption in the UV-visible section and optical absorption shows a slight blue shift towards a longer wavelength. The development of optimal band gap of TiO₂-ZnO thin films in the solar spectrum as a function of Zn²⁺ ion concentration increases the absorption of light in DSSC cells

3.7 X-ray photoelectron spectroscopy

The elemental composition and valence state of the components associated with TiO₂-ZnO nanocomposite were confirmed using XPS data. Figure 1.8(a) depicts a complete scan spectrum of the sample AB3, with the C1s peak located at 284.8 eV [33]. The observed values assigned to chemical element state of Ti⁴⁺ in a TiO₂, were found to be in good reliability with two peaks in Fig. 1.8(c), which correspond to Ti 2p_1/2 and Ti 2p_3/2 [34]. The Zn 2p_1/2 and Zn 2p_3/2 spectra from the TiO₂-ZnO nanocomposite of sample AB3 are depicted in Fig. 1.8(d). The recognizable peaks are situated at respective energies of 1045.43 and 1022.16 eV [35]. Figure 1.8(d) depicts the scan spectra for the O1s region. There are two fitting curves observed, the higher energy peak corresponds to oxygen in an oxygen deficient location, and the lower energy peak may be an indication of a defective oxide component. [36].

3.8 Photoelectrochemical performance of TiO₂/ZnO DSSCs

The thin film photoelectrochemical solar cells have comprehensive pertinence due to easy and cost-effective construction with appropriate redox couples. Thus, photoelectrochemical solar cell performance with semiconductors under investigation can be applied as a prompt path to analyze the PCE of DSSC devices. The photo-electrode was an orange N₃ dye-sensitized TiO₂-ZnO nanocomposite coated on FTO, and the counter electrode was a graphite rod, which was essential as a promoter for the reduction of I₃^⁻ ions. The I⁻/ I₃^⁻redox couple improves charge transfer between I⁻ and I³⁻. it was discovered that the contribution to the overall charge transport current was dominated. when the concentration of the redox couple's reduced and oxidized counterparts was equal and high [37]. A potentiostat was used to test the current density-voltage parameters of the dye-sensitized TiO₂-ZnO nanocomposite under 20 mW/cm² of tungsten filament lamp illumination.

In the TEM data for the TiO₂-ZnO nanocomposite, the linked interconnected nanorods absorb ample light during surface photon irradiation. A use for this kind of morphology of dye-sensitized solar cells improves the photovoltaic performance. The pictorial mechanism of the N₃ dye-sensitized TiO₂-ZnO thin film is already shown in graphical abstract. A working electrode, graphite rod acting as a counter electrode, and an equimolar solution of 0.1 M I⁻/ I₃^⁻ works as a redox mediator made up a PEC cell. In dark, the built DSSC cell displays rectifying properties parallel to a diode.

The J-V computation of dye-sensitized TiO₂-ZnO nanocomposite photoanodes are shown in Fig. 1.9. The A, AB1, AB2, AB3, and B based DSSC could only display photovoltage when illuminated by visible light. Equations (1.3) and (1.4) [32, 38] were used to calculate the DSSC parameter fill factor and conversion efficiency, respectively.

$$\:FF=\:\frac{{J}_{max}\times\:{V}_{max}}{{J}_{sc}\times\:{V}_{oc}}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\dots\:\left(1.3\right)$$

$$\:\eta\:\:\%=\:\frac{{J}_{sc}\times\:{V}_{oc}}{{P}_{in}}\times\:FF\times\:100\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\dots\:\left(1.4\right)$$

Where J_max = denoted for the maximum current,

V _max = denoted for maximum voltage,

η = the conversion efficiency,

J _sc = the short circuit current density,

V _oc = the open-circuit voltage, and

‘P_in’=intensity of the incident light.

The photocurrent of the composite sample increased from 2.36 mA/cm² to 3.25 mA/cm², and the photovoltage increased from 641.87 mV to 946.96 mV for AB1, AB2, and AB3 samples of TiO₂-ZnO nanocomposite photoanode. Sample A has a 4.803% conversion efficiency while sample B has a 4.671% conversion efficiency. The defect states and series resistance, as well as reduced bandgap brought on by small-sized nanorod formations with a smaller surface area, may have contributed to low performance. The conversion efficiency of the AB1 and AB2 samples responded with values of 5.256% and 7.386% which were significantly greater than average. It may be connected to a modification in the nanorod's length and systematic narrowing of bandgap than A. The effectively adding more near-UV spectral components improves the electrochemical behavior. Sample AB3 photoconversion efficiency was increased to 7.386%. The network of interconnected nanorodes efficiently absorbs light, increasing the number of electron-hole pairs across. The AB3 sample of TiO₂-ZnO nanocomposite thin film, which has minimal bandgap and the greatest ability to absorb N₃ dye, was primarily responsible for increase the PEC of DSSCs. The light absorption layer with the least grain boundaries is afforded by nanorods. The AB3 sample had a larger surface area, which boosted N₃ absorption and improved conversion efficiency.

Table 1.4

PEC parameters of samples A, AB1, AB2, AB3, and B
Sample Code	$\:{J}_{sc}$ (mA/cm²)	$\:{V}_{oc}$ (mV)	F (%)	DSSCs Conversion efficiency (%)
A	2.25	821.05	52	4.803
AB1	2.36	641.87	53	5.256
AB2	3.22	896.09	47	6.780
AB3	3.25	946.96	48	7.386
B	2.23	790.44	53	4.671

The values of the DSSC conversion efficiency are shown in Table 1.4 for the samples A, AB1, AB2, AB3, and B, respectively. By altering the width of linked nanorods with increasing crystallinity, the conversion efficiency was increased from 4.671–7.386%. A significant amount of surface area for light absorption might be provided by the shape of the linked nanorods. [39]. Sample AB3 is uniform and compact, and as a result, degenerate electrons build up at FTO-TiO₂-ZnO nanocomposite-dye inter phase, gradually shifting the potential to higher value. In thin films of TiO₂-ZnO nanocomposite, the formation of nanorod morphology, which was aided by AB3, results in the highest photoconversion efficiency [40, 41].

3.9 Electrochemical Impedance Spectroscopy of TiO₂-ZnO DSSCs

To further evaluate charge transfer characteristics EIS technique is used to precisely scrutinize the charge transfer resistance (R_ct) of the fabricated cells. Using the EIS approach, the electrochemical properties of A, AB1, AB2, AB3, and B were evaluated. In a three-electrode cell assembly, dye coated TiO₂-ZnO nanocomposite is used as working electrode, Ag/AgCl as reference electrode, and graphite rod as auxiliary electrode. Electrochemical reactions occurred in the I ̄/I₃̄ redox pair. Figure 1.10 displays the Nyquist plots for the A, AB1, AB2, AB3, and B samples.

Its three portions represent the high, middle, and low-frequency ranges. Initial impedance is coupled to series resistance (Rs) of the photocathode. An example Randles circuit linked with Warburg resistance shown in the inset of Fig. 1.10. The electrode configuration that takes part in the electron interaction between the dye-sensitized photoelectrode and the electrolyte has an ohmic series resistance called Rs. The intermediate frequency region is consistent with charge transfer resistance (R_ct) and double layer capacitance (C_dl) at the TiO₂-ZnO photoanode-electrolyte interface. The low-frequency region connected to the system's Warburg resistance (Zw). Warburg impedance (Zw), which was brought on by ion diffusion in the electrolyte, was visible in the low-frequency region.

Table 1.5

EIS measurement parameters of sample A, AB1, AB2, AB3, and B DSSC obtained by fitting the data to Randles circuit
Sample	R_s (Ω cm²)	R_ct (Ω cm²)	C_dl (10^− 9) (F/cm²)	Z_w (10^− 5) (mMho)
A	12.24	156.24	125.8	25.65
AB1	2.24	96.42	120.54	10.24
AB2	4.14	48.32	96.42	5.48
AB3	3.17	20.14	40.25	3.27
B	4.15	265.12	142.31	36.24

The Randles circuit can be used to assess magnitudes of R_s, R_ct, C_dl, and Z_w related to DSSCs. The results are tabulated in Table 1.5 using EIS data. The decreased values of Rs and Rsh attributable to a lowering charge transfer at the FTO/ TiO₂-ZnO-dye crossing point for T3 in comparison to A, AB1, AB2, AB3, and BDSSC. In a Nyquist plot, it is well known that the lower semicircle has a lower Rct. In comparison to the A, AB1, AB2, AB3, and B samples, the semicircle of the AB3 sample is narrower. A smaller semicircle indicates that charge transfer resistance of DSSC system has decreased. The decreased R_ct for AB3 is related to improvements in the crystallinity and formation of nanoflake structures that control the diffusion channel length. When R_ct decreases, the electrical conductivity increases, and the photo-conversion efficiency rises. Due to the TiO₂-ZnO-dye photocathode's surface compactness and nanoflakes-like shape, charge transfer resistance has decreased. [42–44].

N3 dye-sensitized TiO₂-ZnO nanocomposites were effectively synthesised using a precipitation method and a screen-printing technique. According to the structural analyses, titanium oxide and zinc oxide take on the mixed phase of rutile and hexagonal wurtzite structure respectively. The surface morphology confirmed TiO₂-ZnO composite as nanorod shape modifiers, and that it is dependent on a concentration of different width sizes. As determined by EDS, deposited TiO₂-ZnO nanocomposite is stoichiometric. TEM further confirms interconnected nanorod-like morphology of sample AB3. Further optical absorption study reveals the energy of electronic transition with bandgap of 3.3 to 2.95 eV. Development of interconnected nanorods, such as the TiO₂-ZnO system, has achieved an even greater increase in conversion efficiency compared to small nanocrystal form which is prerequisite for the enhanced PEC performance of AB1 to AB3 DSSC was associated with the alteration width in nanorods and the decrease in the band gap energy. The AB3 sample of DSSC shows highest photo-conversion efficiency of 7.386%. The use of an N₃ dye in a TiO₂-ZnO-based DSSC was used to illustrate a simple way of harvesting solar energy.

Declaration conflict of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors express their profound gratitude to their respective institutions for the provision of advanced facilities. This research was conducted independently, without any external funding or sponsorship.

Data availability statement

The data will be made available when requested.

Nimpoeno WA, Lintang HO, Yuliati L (2020) AIP Conference Proceedings, 2237, 020048
Lee SY, Kang D, Jeong S, Do HT, Kim JH (2020) ACS omega. 18;5(8):4233-41
Zulfikar MA, Chandra AD, Setiyanto H, Handayani N, Wahyuningrum D (2020) Songklanakar J Sci Technol, 1;42(2)
Regan BO, Gratzel M (1991) Nat (ISSN 0028–0836), 353, 737–740
Kakiage K, Aoyama Y, Yano T, Oya K, Fujisawa J, Hanaya M (2015) Chem Commun (Camb) 51:15894–15897
Gurusamy S, Kulanthaisamy MR, Hari DG, Veleeswaran A, Thulasinathan B, Muthuramalingam JB, Balasubramani R, Chang SW, Arasu MV, Al-Dhabi NA, Selvaraj A (2020) J Photochem Photobiol B Biol 193:118–130
Moradi S, Aberoomand-Azar P, Raeis-Farshid S, Abedini-Khorrami S, Givianrad MH (2016) J Saudi Chem Soc 20(4):373–378
Pugazhendhi K, D’Almeida S, Kumar PN, Mary JS, Tenkyong T, Sharmila DJ, Madhavan J, Shyla JM (2020) Mater Res Express 27(4):045053
Jiang X, Liu H, Sun H, Duan L, Zhao X (2020) Mater. Res. Express, 1;8(3), 288–293
Sygkridou D, Vitoratos E (2020) In Proceedings of the 15th IEEE International Conference on Nanotechnology, July 27–30, Rome, Italy: pp. 1370–1373
Mali SS, Betty CA, Bhosale PN, Patil PS (2012) Electrochim Acta 59:113–120
Chatterjee S, Webre WA, Patra S, Rout B, Glass GA, D’Souza F, Chatterjee S (2020) J Alloys Compd 826:154188
Syrrokostas G, Leftheriotis G, Yianoulis P (2014) Renew Energy 72:164–173
Horiuchi H, Katoh R, Hara K, Yanagida M, Murata S, Arakawa H, Tachiya M (2003) J Phys Chem B 107:2570–2574
Xie Y-L, Li Z-X, Xu Z-G, Zhang H-L (2021) Electrochem Commun 13(8):788–791
Mali SS, Kim H, Shim CS, Bae WR, Tarwal NL, Sadale SB, Patil PS, Kim JH, Hong CK (2013) CrystEngComm 15, 5660–5668
Parale VG, Kim T, Phadtare VD, Yadav HM, Park HH (2019) J Mol Liq 277:424–433
Wategaonkar SB, Pawar RP, Parale VG, Nade DP, Sargar BM, Mane RK (2020) Mater.Today-Proc. 23, 444–449
Kim SS, Yum JH, Sung YE (2005) J Photochem Photobiol Chem 171:269–273
Campbell WM, Jolley KW, Wagner P, Wagner K, Walsh PJ, Gordon KC, Schmidt-Mende L, Nazeeruddin MK, Wang Q, Gra1tzel M, Officer DL (2007) J Phys Chem C 111:32–34
Kharkwal D, Sharma N, Gupta S, Negi CS (2021) Sol Energy 230:1133–1140
Nazeeruddin MK, Angelis FD, Fantacci S, Selloni A, Viscardi G et al (2005) J Am Chem Soc 127:16835–16847
Nazeeruddin MK, Baker RH, Liska P, Grätzel M (2003) J Phys Chem B 107:8981–8987
Nazeerudding MK, Pechy P, Renouard T, Zakeeruddin SM, Humphrey-Baker R, Comte P et al (2001) J Am Chem Soc 123:1613–1624
Wang ZS, Yamaguchi T, Sugihara H, Arakawa H, Langmuir (2005) 21, 4272–4276
Chiba Y, Islam A, Watanabe Y, Komiya R, Koide N, Han L (2006) J Appl Phys 45:L638–L640
Zhou H, Wu L, Gao Y, Ma T (2011) J Photochem Photobiol A: Chem 219:188–194
Nazeeruddin MK, Kay A, Rodicio I, Humphry-Baker R, Muller E, Liska P, Vlachopoulos N, Gra¨tzel M (1993) J Am Chem Soc 115:6382
Nguyen HM, Nguyen DN, Kim N (2010) Adv Nat Sci Nanosci Nanotechnol 1:025001
Pakhare KS, Sargar BM, Potdar SS, Sharma AK, Patil UM (2019) J Electron Mater 48(10):6269–6279
Kathirvel S, Su C, Shiao Y, Lin Y, Chen B, Li W (2016) Sol Energy 132:310–320
Thate AG, Pakhare KS, Patil SS, Bhuse VM (2022) Res Chem Intermed 49:147–168
Jang HD, Kim SK, Chang H, Roh KM, Choi JW, Huang J (2012) Biosens Bioelectron 38:184–188
Grohmann I, Peplinski B, Unger W (1992) Surf Interface Anal 19:591
Yan X, Zou C, Gao X, Gao W (2012) J Mater Chem 22:5629
Biesinger MC, Lau LWM, Gerson AR (2010) Appl Surf Sci 257:887–897
Ryuji Kawano H, Matsui C, Matsuyama A, Sato (2004) Md. Abu Bin Hasan Susan, Nobuo Tanabe, Masayoshi Watanabe. J Photochem Photobiol A 164:87–92
Thate AG, Pakhare KS, Patil SS, Bhuse VM (2023) Environmentally benign synthesis of TiO₂ -ZnO nanocomposite for efficient dye-sensitized solar cell. Mater Res Express 10:055001
Patil SS, Mali SS, Hong CK, Bhosale PN (2020) Mater. Sci. Semicond. Proc. 105, 104727
Cen J, Wu Q, Yan D, Zhang W, Zhao Y, Tong X, Liu M, Orlov A (2019) RSC Adv 9:899
Wang N, Wang D, Li M, Shi J, Li C (2014) 6, 2061
Patil SS, Mane RM, Khot KV, Mali SS, Kook Hong C, Bhosale PN (2021) Sol Energy 220:371
Chu J, Lu D, Wang X, Wang X, Xiong S (2017) J Alloys Compd 702:568–572
Kishore R, Cao X, Zhang X, Hutter AB (2019) Electrochemical water oxidation on WO₃ surfaces: A density functional theory study. Catal Today 321:94–99

graphicalabstract.jpg
Graphical abstract

Download PDF

Version 1

posted

You are reading this latest preprint version

TiO2-ZnO rodlike nanocomposite as photoanode in DSSC yielding 7.38% PEC with N3 dye

Status:

Version 1

Abstract

Figures

1. Introduction

2. Experimental

2.1 Materials and methods

2.2 Characterization

3. Result and Discussion

3.1 UV–Visible spectroscopy of N₃ dye

3.2 X-ray diffraction study

3.3 Morphological studies

3.4 HR-TEM

3.5 Compositional studies

3.6 UV-Visible spectroscopy

3.7 X-ray photoelectron spectroscopy

3.8 Photoelectrochemical performance of TiO₂/ZnO DSSCs

3.9 Electrochemical Impedance Spectroscopy of TiO₂-ZnO DSSCs

4. Conclusion

Declarations

Acknowledgements

Data availability statement

References

Supplementary Files

Status:

Version 1

TiO2-ZnO rodlike nanocomposite as photoanode in DSSC yielding 7.38% PEC with N3 dye

Status:

Version 1

Abstract

Figures

1. Introduction

2. Experimental

2.1 Materials and methods

2.2 Characterization

3. Result and Discussion

3.1 UV–Visible spectroscopy of N3 dye

3.2 X-ray diffraction study

3.3 Morphological studies

3.4 HR-TEM

3.5 Compositional studies

3.6 UV-Visible spectroscopy

3.7 X-ray photoelectron spectroscopy

3.8 Photoelectrochemical performance of TiO2/ZnO DSSCs

3.9 Electrochemical Impedance Spectroscopy of TiO2-ZnO DSSCs

4. Conclusion

Declarations

Acknowledgements

Data availability statement

References

Supplementary Files

Status:

Version 1

3.1 UV–Visible spectroscopy of N₃ dye

3.8 Photoelectrochemical performance of TiO₂/ZnO DSSCs

3.9 Electrochemical Impedance Spectroscopy of TiO₂-ZnO DSSCs