Electrochemical energy storage has attracted much attention due to the common recognition of sustainable energy development.

Titanium dioxide (TiO₂) is a commonly used wide bandgap semiconductor material for energy and environmental applications. Although it is a promising candidate for photovoltaic and photocatalytic applications, its overall performance is still limited due to low mobility of porous TiO₂ and its limited spectral response. This limitation can be overcome by several ways, one of which is doping that could be used to improve the light harvesting properties of TiO₂ by tuning its bandgap. TiO₂ doped with elements, such as alkali-earth metals, transition metals, rare-earth elements, and nonmetals, were found to improve its performance in the photovoltaic and photocatalytic applications. Among the doped TiO₂ nanomaterials, transition metal doped TiO₂ nanomaterials perform efficiently by suppressing the relaxation and recombination of charge carriers and improving the absorption of light in the visible region. This work reports the possibility of enhancing the performance of TiO₂ towards Dye Sensitised Solar Cells (DSSCs) and photocatalytic degradation of methylene blue (MB) by employing Zn doping on TiO₂ nanomaterials. Zn doping was carried out by varying the mole percentage of Zn on TiO₂ by a facile solvothermal method and the synthesized nanomaterials were characterised. The XRD (X-Ray Diffraction) studies confirmed the presence of anatase phase of TiO₂ in the synthesized nanomaterials, unaffected by Zn doping. The UV-Visible spectrum of Zn-doped TiO₂ showed a red shift which could be attributed to the reduced bandgap resulted by Zn doping. Significant enhancement in Power Conversion Efficiency (PCE) was observed with 1.0 mol% Zn-doped TiO₂ based DSSC, which was 35% greater than that of the control device. In addition, it showed complete degradation of MB within 3 h of light illumination and rate constant of $1.5466\times {10}^{-4}{s}^{-1}$ resembling zeroth order reaction. These improvements are attributed to the reduced bandgap energy and the reduced charge recombination by Zn doping on TiO₂.

In this study, P25-titanium dioxide (TiO₂) was doped with ruthenium (Ru) by systematically varying the Ru content at 0.15, 0.30, 0.45 and 0.6 mol%. The synthesized Ru-doped TiO₂ nanomaterials have been characterized by X-ray diffraction (XRD), Raman spectroscopy, energy-dispersive X-ray (EDX) analysis, UV-visible (UV–Vis) spectroscopy, and electrochemical impedance (EIS) spectroscopy. The XRD patterns of undoped and Ru-doped TiO₂ nanomaterials confirm the presence of mixed anatase and rutile phases of TiO₂ while EDX spectrum confirms the presence of Ti, O and Ru. Further, UV-visible absorption spectra of doped TiO₂ nanomaterial reveal a slight red shift on Ru-doping. The short circuit current density (J_SC) of the cells fabricated using the Ru-doped TiO₂ photoanode was found to be dependent on the amount of Ru present in TiO₂. Optimized cells with 0.3 mol% Ru-doped TiO₂ electrodes showed efficiency which is 20% more than the efficiency of the control cell (η = 5.8%) under stimulated illumination (100 mWcm⁻², 1 sun) with AM 1.5 filter. The increase in J_SC resulted from the reduced rate of recombination upon doping of Ru and this was confirmed by EIS analysis.

This study reports a facile impregnation method for synthesizing Ni-doped TiO₂nanomaterials using P25-TiO₂as a starting material. The as prepared nanomaterials were subjected to structural and optical characterizations and subsequently employed in photovoltaic studies. X-ray diffraction (XRD) and Raman studies confirmed that Ni doping did not alter the anatase and rutile contents of P25-TiO₂. Also, the presence of the constituent dopants and their ionic states were confirmed by Energy-Dispersive X-ray (EDX) and X-ray photoelectron (XPS) spectroscopies. Topographic Atomic Force Microscopic (AFM) images illustrated that Ni doping had increased the surface roughness of the TiO₂. Optical characterization by UV-Visible spectroscopy revealed that the Ni doping had caused red shift in light absorption due to reduced TiO₂bandgap and improved the dye adsorption on TiO₂films. Then, the photocurrent–photovoltage property of the fabricated devices was investigated and the optimized 0.10 wt% Ni-doped TiO₂photoanode based device exhibited pronounced power conversion efficiency (PCE) of 6.29% under air mass (AM) 1.5 conditions (100 mWcm⁻², 1 sun). Improved charge transport properties were also observed by the electrochemical impedance spectroscopic (EIS) study for the device with optimized Ni-doped TiO₂compared to the control device.

Doping is a unique strategy to modulate the optical and electronic properties of semiconducting materials. This study reports a facile approach to fabricate nitrogen-doped TiO₂ (N-doped TiO₂) photoanode for DSSC application. A solid-state reaction was employed to synthesize a series of N-doped TiO₂ nanoparticles with different volumetric ratios of nitrogen dopant and the TiO₂ host. The NH₄OH as a nitrogen dopant was combined with P25-TiO₂ via grinding followed by calcination at 500°C. The synthesized nanoparticles were extensively characterized by XRD, XPS, EDX, SEM, and TEM techniques. XRD results suggested that the incorporation of nitrogen had not altered the structure of the TiO₂ lattice, and the presence of nitrogen was confirmed through the XPS and EDX spectroscopies. SEM and TEM images, obtained before and after N doping, showed that N-doped TiO₂ nanoparticles with low amounts of NH₄OH (10 and 20 μL) had retained their spherical shapes and sizes while use of higher amounts of the N dopant (30 and 40 μL) had led to agglomeration of nanoparticles. BET and BJH analyses revealed that the optimized N-doped TiO₂ with 20 μL of NH₄OH (20N-TiO₂) possesses the highest average pore diameter of 15.99 nm. Furthermore, the UV-visible spectroscopic analysis confirmed a red shift in the optical absorption edge on N doping and the corresponding bandgap reduced from 3.15 to 2.94 eV with increase in the amount of NH₄OH from 0 to 40 μL. Eventually, DSSCs were fabricated using the prepared pure TiO₂ and N-doped TiO₂ photoanodes, N719 dye, electrolyte, and Pt counter electrode, followed by investigating their performance under simulated irradiation with 100 mW/cm² intensity with AM 1.5 filter. The photoanode doped with 20 μL of NH₄OH (20N-TiO₂) exhibited the highest power conversion efficiency (PCE) of about 6.16%, which was 20% higher than that of the control device, with improved . This enhancement in could be predominantly attributed to higher dye uptake along with marginal contribution by reduced rate of recombination. Among the reported studies on DSSCs with N-doped P25-TiO₂ photoanodes, our method gives the best efficiencies for the DSSCs.

In this study, an iodine-free 1-butyl-3-methylimidazolium iodide (BmimI) ionic liquid, modified with acetonitrile (AN), was employed as a redox mediator using a facile approach to enhance DSSC performance. The optical properties of BmimI-AN(1:2) electrolyte (BmimI: AN = 1:2 w/w) indicate low absorption and high transmittance in the visible region. In addition to the UV-Vis spectra, Raman spectra also confirm the presence of the in-situ generated \(\:{I}_{3}^{-}\) ions, which are sufficient to complete the reaction mechanism in DSSCs. Conductivity measurements revealed that the BmimI-AN(1:2) electrolyte possesses excellent ionic conductivity compared to BmimI and standard commercial \(\:{I}^{-}/{I}_{3}^{-}\) electrolytes. The photovoltaic performances of the fabricated devices were analysed under simulated irradiation at an intensity of 100 mWcm^–2 using a Xe lamp with an AM 1.5 filter. The BmimI-AN(1:2) electrolyte led to a higher power conversion efficiency (PCE) in DSSC, reaching up to 6.26 ± 0.21%, primarily due to improvements in V_OC and J_SC. Apart from the transparent nature of the BmimI-AN(1:2) electrolyte, it suppresses charge recombination, resulting in a higher electron lifetime in DSSCs. Moreover, DSSCs with the BmimI-AN(1:2) electrolyte exhibited short-term stability comparable to that of standard commercial electrolytes under ambient conditions, with the potential for further improvement through future optimization.