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The cost‐effective, robust, and efficient electrocatalysts for photoelectrochemical (PEC) water‐splitting has been extensively studied over the past decade to address a solution for the energy crisis. The interesting physicochemical properties of CuO have introduced this promising photocathodic material among the few photocatalysts with a narrow bandgap. This photocatalyst has a high activity for the PEC hydrogen evolution reaction (HER) under simulated sunlight irradiation. Here, the recent advancements of CuO‐based photoelectrodes, including undoped CuO, doped CuO, and CuO composites, in the PEC water‐splitting field, are comprehensively studied. Moreover, the synthesis methods, characterization, and fundamental factors of each classification are discussed in detail. Apart from the exclusive characteristics of CuO‐based photoelectrodes, the PEC properties of CuO/2D materials, as groups of the growing nanocomposites in photocurrent‐generating devices, are discussed in separate sections. Regarding the particular attention paid to the CuO heterostructure photocathodes, the PEC water splitting application is reviewed and the properties of each group such as electronic structures, defects, bandgap, and hierarchical structures are critically assessed.

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Electron transport in the porous nanostructured titanium oxide, as a main concern in the dye-sensitized solar cells, was investigated by random walk simulation. Geometrically disordered nanoparticle networks with random distribution of energy was generated and utilized for simulations. Dependency of the diffusion coefficient (D ef ) on the nanoparticles size, grains connectivity, and the network porosity was completely studied in two cases: traps are placed mainly on the surface or in the volume of the nanoparticles. It was shown that the D ef is independent of nanoparticle size for both surface and volume diffusion. We have shown in this study that increasing the D ef with the particle size is a consequence of the trap-filling (electronic) effect and not a geometrical effect. The role of electronic effect in electron transport in nanoporous materials has been highlighted in this work.

Nonlinear recombination in dye-sensitized solar cells was studied from a fundamental point of view. A model based on Marcus theory was used to describe the recombination from both conduction band and trap states. By combination of this model with the empirical form of nonlinear recombination, dependency of the reaction order (β) on the microscopic parameters of the solar cell was investigated. It was analytically shown that β is always less than unity and also depends on the quasi Fermi-level in semiconductors. By this nonconstant β, the dependency of the ideality factor (m), electron diffusion length (L n ), and the electron lifetime (τ n ) on the Fermi-level were studied. It was discussed that the nonconstant β can explain the flattening of the L n at high Fermi-level, as observed in some recent experimental works. For the lifetime, it was shown that only the quantity τ n /m is accessible in the common open-circuit voltage decay method. It was also shown that the lifetime and the ideality factor can be obtained by the well-known charge extraction method.