Graphene‑Based Materials in Plasmonic Dye‑Sensitized Solar Cells: A 2026 Graduate‑Level Review of rGO, Ternary Nanocomposites, and Pt‑Free Counter Electrodes

1. Introduction: The Role of Graphene in Next‑Generation DSSCs

Graphene and its derivatives – pristine graphene, graphene oxide (GO) and reduced graphene oxide (rGO) – have attracted enormous interest in photovoltaic research due to their exceptional electrical, optical and mechanical properties. Unlike the first major wave of graphene research in DSSCs around 2010–2015, which primarily focused on replacing costly Pt counter electrodes or enhancing TiO₂ conductivity with modest success, the 2024–2026 period has witnessed a paradigm shift toward multi‑functional nanocomposite architectures. Today, rGO is no longer just a conductive additive; it serves as:

• a template for controlled nanoparticle growth,
• a charge‑transport highway that suppresses electron–hole recombination,
• a porosity enhancer for superior dye loading,
• and a plasmonic co‑catalyst when combined with noble metals.

This review synthesises the most significant breakthroughs from 2025 and 2026, focusing on three key areas: plasmonic photoanodes, Pt‑free counter electrodes, and heteroatom‑doped graphene architectures. Each case study is presented with its underlying physical mechanisms, efficiency metrics and practical implications for graduate‑level researchers.

2. Fundamental Physics: Why rGO Works in DSSCs

Before examining specific devices, it is useful to recall the fundamental advantages of rGO over conventional materials in DSSC architectures.

Electron transport and recombination suppression. The power conversion efficiency (PCE) of a DSSC is critically limited by the competition between electron transport through the TiO₂ network and recombination with oxidized dye molecules or the I₃⁻/I⁻ electrolyte. Pristine TiO₂ possesses a high density of surface traps – oxygen vacancies and under‑coordinated Ti sites – that impede electron diffusion and act as recombination centres. When rGO (a two‑dimensional sp²‑hybridised carbon sheet with residual oxygen functional groups) is introduced into the photoanode, it creates a percolation network of highly conductive pathways. Electrons photogenerated in the dye can transfer rapidly to the rGO sheets and then to the external circuit, bypassing the slower transport through the TiO₂ mesoporous network. Electrochemical impedance spectroscopy consistently shows a reduction in charge‑transfer resistance (R_ct) and an increase in electron lifetime (τ_e) upon rGO incorporation.

Surface area and dye loading. The specific surface area of rGO (typically 200–500 m² g⁻¹) is comparable to that of mesoporous TiO₂ nanoparticles. However, when rGO is blended with TiO₂, the two materials form a hierarchical pore structure – micropores from the rGO interlayer spacing and mesopores from the TiO₂ nanoparticle network. This bimodal porosity leads to enhanced dye adsorption, as evidenced by UV–Vis absorption measurements of dye‑loaded photoanodes.

Plasmonic synergy. Perhaps the most exciting development in 2025–2026 has been the deliberate design of rGO–metal–semiconductor ternary nanocomposites. In such systems, rGO plays a triple role: (i) as a substrate for homogeneous dispersion of plasmonic nanoparticles (Au, Ag), preventing agglomeration; (ii) as a charge collector that rapidly shuttles hot electrons generated by plasmon decay; and (iii) as a band‑structure modifier that influences the local dielectric environment around the metal nanoparticles, thereby tuning the LSPR peak position.

3. Case Study I: Ternary TiO₂–rGO–Ag Photoanode (2025)

A comprehensive study published in the Journal of Electronic Materials (2025, Volume 54) demonstrated the systematic optimisation of TiO₂–rGO–Ag ternary nanocomposites for DSSC photoanodes. The nanocomposites were synthesised via a solvothermal method with simultaneous in‑situ reduction of graphene oxide and silver ions using ammonia as a reducing agent.

3.1 Structural and Optical Characterisation

Raman spectroscopy confirmed the successful reduction of GO to rGO (increase in the I_D/I_G ratio). XRD patterns showed the characteristic peaks of anatase TiO₂, metallic Ag and the (002) reflection of rGO. SEM and TEM imaging revealed that Ag nanoparticles (20–30 nm) were uniformly distributed on the rGO sheets and TiO₂ nanoparticles. UV–Vis spectroscopy showed a broad absorption tail extending into the visible and near‑infrared region, with the LSPR peak of Ag at approximately 450–500 nm.

3.2 Photovoltaic Performance

The optimal composition was 1 wt.% rGO and 2 wt.% Ag, achieving a PCE of 6.3% under AM 1.5 illumination – a substantial improvement over the pure TiO₂ reference. EIS measurements showed a lower charge‑transfer resistance and an increased electron lifetime (from 8 ms to 18 ms). The electron diffusion coefficient increased by a factor of 2.5.

3.3 Physical Mechanism of the Ternary Synergy

The enhancement follows a three‑step process: (1) LSPR of Ag enhances the near‑field, increasing dye excitation; (2) electrons inject into TiO₂ then rapidly transfer to rGO sheets; (3) rGO suppresses recombination by physically separating TiO₂ from the electrolyte and acting as a hole‑blocking layer.

4. Case Study II: Au/rGO‑Decorated TiO₂ Nanorod Arrays (2025)

A study in Materials Science and Engineering: B investigated vertically aligned TiO₂ nanorod (NR) arrays decorated with Au nanoparticles and rGO. The Au/rGO@TiO₂ NR photoanode achieved a PCE of 6.74% – a 55.3% enhancement compared to bare TiO₂ NR. IPCE measurements revealed a broad enhancement across the visible spectrum (450–700 nm), with maximum near the Au LSPR peak (~550 nm). The 1D architecture minimises grain boundaries, and rGO passivates surface defects while enhancing light scattering.

5. Beyond Photoanodes: rGO in Counter Electrodes (2025–2026)

Remarkable progress has been made in using rGO‑based composites as Pt‑free counter electrodes (CEs). Two standout studies are highlighted below.

5.1 NiS₂@rGO – Surpassing Platinum

A 2026 study in the Journal of Materials Science: Materials in Electronics reported NiS₂ nanoparticles (10–20 nm) uniformly anchored on rGO. The NiS₂@rGO CE delivered a charge‑transfer resistance of only 0.18 Ω, a J_SC of 16.5 mA cm⁻², and a maximum PCE of 7.2%, surpassing the Pt reference (6.7%). The device retained 95% of its initial efficiency after 1000 h of continuous illumination.

5.2 FeS₂/rGO Nanoplates: Another Pt‑Surpassing System

A 2025 study in Materials Today Sustainability used hexagonal FeS₂ nanoplates integrated onto rGO sheets. The FeS₂/rGO hybrid achieved a PCE of 6.23%, exceeding the Pt counterpart (5.89%). The synergy arises from catalytically active FeS₂ edge sites and the conductive rGO framework.

5.3 Physical Chemistry of Sulfide–rGO Synergy

DFT calculations show that the Fermi level of rGO aligns with the conduction band edges of transition metal sulfides, creating a type‑II heterojunction that facilitates electron transfer. The rGO also prevents sulfide nanoparticle agglomeration, preserving active edge sites for the I₃⁻ reduction reaction.

6. Alternative Architectures: Graphene Oxide in Photoanode Design

While rGO is preferred for high conductivity, pristine GO can also enhance DSSCs. A 2025 review highlighted that GO integrated with metal‑organic frameworks (MOF‑5) in TiO₂ photoanodes resulted in a PCE enhancement of 5.56 times compared to pure devices. GO’s oxygen functional groups act as anchor points for dye molecules and metal nanoparticles, though an optimal reduction degree is needed to balance dye anchoring and charge transport.

7. Summary Table of Key Achievements (2025–2026)

8. Future Perspectives and Research Directions

• Scalability of synthesis: Moving from milligram to industrial scale while maintaining nanoparticle dispersion.
• Long‑term stability beyond 1000 h: Accelerated ageing tests under combined thermal and illumination stress.
• Quaternary nanocomposites: e.g., TiO₂–rGO–Au–Ag or MoS₂–rGO–NiS₂ for cascaded charge‑transfer pathways.
• Integration with copper‑based redox shuttles and porphyrin dyes: Potential to push efficiencies toward 12–14%.
• Theoretical modelling: DFT and NEGF simulations to design optimal heterostructures predictively.

9. Conclusions

The 2025–2026 period has solidified the role of rGO as an essential component in high‑performance DSSCs. Three distinct functions have emerged: (1) in photoanodes, rGO enhances transport and suppresses recombination; (2) in 1D architectures, rGO with TiO₂ nanorods yields 55% enhancement; (3) in counter electrodes, rGO‑metal sulfide nanocomposites surpass Pt with lower cost and excellent stability. The field has moved beyond simple “add‑and‑test” studies to rationally designed multi‑component nanocomposites. Future collaboration between synthetic chemists, spectroscopists and device physicists will push DSSCs toward commercial viability.