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The dynamic competition between electron generation and recombination was found to be a bottleneck restricting the development of high-performance dye-sensitized solar cells (DSSCs). Introducing a passivation layer on the surface of the TiO 2 photoelectrode material plays a crucial role in separating the charge by preventing the recombination of photogenerated electrons with the oxidized species. This study aims to understand in detail the kinetics of the electron recombination process of a DSSC fabricated with a conductive substrate and photoelectrode film, both passivized with a layer of nanocrystalline TiO 2 . Interestingly, the coating, which acted as a passivation layer, suppressed the back-electron transfer and improved the overall performance of the integrated DSSC. The passivation layer reduced the exposed site of the fluorine-doped tin oxide (FTO)-electrolyte interface, thereby reducing the dark current phenomenon. In addition, the presence of the passivation layer reduced the rate of electron recombination related to the surface state recombination, as well as the trapping/de-trapping phenomenon. The photovoltaic properties of the nanocrystalline-coated DSSC, such as short-circuit current, open-circuit voltage, and fill factor, showed significant improvement compared to the un-coated photoelectrode film. The overall performance efficiency improved by about 22% compared to the un-coated photoelectrode-based DSSC.The mesoporous oxide photoelectrode material is the heart of a DSSC. It has responsibilities in anchoring the molecules of the dye sensitizer, and it acts as a medium for the transportation of electrons. In recent years, the development of binary and ternary oxide nanostructured photoelectrode materials such as titanium dioxide (TiO 2 ), zinc oxide (ZnO), tin oxide (SnO 2 ), and zinc tin oxide (Zn 2 SnO 4 ) attracted great attention due to their suitable conduction band and unique characteristics for DSC application. As of now, TiO 2 is the semiconductor of choice due to its promising properties such as wide bandgap energy, low cost, abundance, and non-toxic oxides. Moreover, the chemical inertness of TiO 2 makes it possible to allow the dye sensitizer molecule, which commonly has a carboxylate anchoring group, to be attached to the photoelectrode surface. Additionally, other distinguishing features of TiO 2 such as the high relative permittivity of anatase (~30-40) helps in lowering the electrostatic interaction between the injected electrons and oxidized dye molecules, thus reducing the possibilities of electron recombination [5]. Anatase (E g = 3.23 eV), rutile (E g = 3.05 eV), and brookite (E g = 3.26 eV) are three crystalline TiO 2 polymorphs that naturally exist. Brookite with an orthorhombic structure is difficult to synthesize in the laboratory compared to anatase and rutile. Even though rutile and anatase have the same tetragonal structure, a higher Fermi level of anatase by 0.1 eV compared to rutile makes it more desirable for DSSC application [6].When the photosensitized dye receives e...

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Dye-sensitized solar cells (DSSCs) have emerged to become one of the most promising alternatives to conventional solar cells. However, long-term stability and light-to-energy conversion efficiency of the electrolyte in DSSCs are the main challenges in the commercial use of DSSCs. Current liquid electrolytes in DSSCs allow achieving high power conversion efficiency, but they still suffer from many disadvantages such as solvent leakage, corrosion and high volatility. Quasi-solid state electrolytes have therefore been developed in order to curb these problems. A novel polymer electrolyte composed of biobased polymer chitosan, poly(vinylidene fluoridehexafluoropropylene) (PVdF-HFP), 1-methyl-3-propylimidazolium iodide ionic liquid and iodide/tri-iodide redox salts in various compositions is proposed in this study as a quasi-solid state electrolyte. Fourier transform infrared microscopy (FTIR) studies on the polymer electrolyte have shown interactions between the redox salt and the polymer blend. The quasi-solid state electrolyte tested in DSSCs with an optimised weight ratio of PVdF-HFP:chitosan (6:1) with ionic liquid electrolyte PMII/KI/ I 2 has shown the highest power conversion efficiencies of 1.23% with ionic conductivity of 5.367 × 10 −4 S · cm −1 demonstrating the potential of using sustainable bio-based chitosan polymers in DSSCs applications.

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