Summary During the recent period of time, dye sensitized solar cells (DSSCs) have become an exciting invention to meet our energy demands. Its reasonable cost of production and easy fabrication make it a powerful competent to the conventional solar cells. But non‐achievement of expected efficiency is the key challenge faced by the scientific society. To overcome this, boundless research is going on the revamping of DSSC. Among the four chief parts of DSSC, the photoanodes gain more attention due to its dual function. Scilicet, it act as a charge carrier and as a surface for dye adsorption as well. Hence photoanode modification plays a crucial role in enhancing the power conversion efficiencies of DSSCs. It comprises of wide bandgap semiconducting metal oxides, among which TiO2 stands out with higher efficiency. Likewise in the case of photosensitizers, metal complex based dyes (mainly ruthenium based) take the lead in augmented efficiency. This paper critically reviews the work on all the metal oxides used as photoanode materials, comparing their band gap with the best efficiencies reported for each and analyzing their advantages and disadvantages. An overview of the performance of DSSCs based on different metal atom doped metal oxide photoanode, incorporation of various carbonaceous materials and different passivating agents has been included. Also, the modification in the photosensitizer has been discussed, examining the reports on organometallics based dyes and metal free organic dyes.

Noncovalent dyads embodied with porphyrin (PPy) and graphene quantum dots (GQDs) were subjected to photophysical studies with the aim of a deep understanding on the electron transfer dynamics in such systems. Peculiarities of a single fluorophore seems to be inadequate in light harvesting materials for various applications which can be rectified by the method of co‐sensitization. In this work Tetraphenylporphyrin (TPP) and Tetranaphthylporphyrin (TNaP) have been utilized for the preparation of the nanohybrid systems to realize the effect of conjugation on the photophysical properties of these materials. The photophysical studies of these nanohybrids such as UV‐Visible spectra, Fluorescence emission spectra and Time‐correlated single photon counting (TCSPC) were carried out. Both the ground and excited state interaction studies indicate an effective association between the two components in these nanohybrids. The photoexcited porphyrin molecules behave as electron donors and GQDs as acceptors and the interaction studies show that the quenching of the porphyrin derivatives occurs through a combined static and dynamic quenching mechanism in the PPy‐GQD nanocomposites. Moreover the extended conjugation in naphthyl system exalted the binding with quantum dots through π‐π interaction and results in augmented electron transfer than that in phenyl nanocomposite. The higher non‐radiative rate constant from TCSPC authenticates the above results. Understanding the photodynamics of electrons in such systems is significant for their effective utilization and practical applications of these materials in light harvesting devices and photocatalysis.

Graphene quantum dots-based nanohybrids (GQD NHs) are considered to be a promising candidate for optoelectronic devices due to their tunable light absorption and pronounced carrier transfer properties. The mechanism of GQD exciton dynamics remains an open problem despite the substantial studies conducted so far. The carrier annihilation process occurring at a femtosecond time scale becomes the greatest hurdle in the path of GQD quantum efficiency. In this quest, we investigated a surface state-assisted photoinduced charge (electron/hole) transfer (PCT) in GQD-(p-methoxy aniline (POMe)/p-nitroaniline (PNO)) nanohybrids by using mainly ultrafast transient absorption spectroscopic technique. The ultrafast PCT time was found to be ∼0.3 ps (ps) and ∼0.4 ps for GQD/PNO and GQD/POMe NHs, respectively. The fastest kinetics observed for GQD/POMe among these systems reveals a more efficient PCT interaction in the GQD/POMe interface than that of GQD/PNO. The higher PCT rate constant (K PCT ) and high negative Gibbs free energy change (ΔG) values observed for GQD/POMe over GQD/PNO further validates the aforementioned results. Cyclic voltammetry along with theoretical studies reveal the thermodynamic viability of PCT in GQD NHs. Outcomes of this study fortify the comprehension of surface state-influenced PCT kinetics of GQD NHs and thus enlarge its optoelectronic applications.

Herein, we scrutinize the photophysical and electronic changes on graphene quantum dots (GQDs) which occurs as a consequence of both type of covalent and non‐covalent functionalization using Tetraaminophenylporphyrin (TAPP). Covalent functionalization resulted in amide bond between GQD and TAPP (GQD‐CONH‐TAPP), while electrostatic interactions, hydrogen bonding and π‐π interactions together contribute to the binding in non‐covalent functionalization. Outstanding difference between both of the functionalized GQDs were observed in their UV‐Visible absorption spectra, photoluminescence (PL) spectra and time‐correlated single photon counting (TCSPC) measurements. GQD‐CONH‐TAPP acts as a charge separated system having C1 point group. In case of GQD‐TAPP, the non‐covalent nanohybrid system, photoinduced electron transfer from TAPP to GQD occurs with a dynamic quenching constant of 21.89×103 M−1 and bimolecular rate constant of 2.77×1014 M−1s−1. Feasibility of this electron transfer is reinforced by the negative ΔGPET value and the theoretical studies.

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