A silver (Ag)-incorporated kesterite CuZnSnS (CZTS) thin film was fabricated by a facile spray pyrolysis method. Crystallographic analyses indicated successful incorporation of various amounts of Ag up to a Ag/(Ag + Cu) ratio of ca. 0.1 into the crystal lattice of CZTS in a homogeneous manner without formation of other impurity compounds. From the results of morphological investigations, Ag-incorporated films had larger crystal grains than the CZTS film. The sample with a relatively low Ag content (Ag/(Ag + Cu) of ca. 0.02) had a compact morphology without appreciable voids and pinholes. However, an increase in the Ag content in the CZTS film (Ag/(Ag + Cu) ca. 0.10) induced the formation of a large number of pinholes. As can be expected from these morphological properties, the best sunlight conversion efficiency was obtained by the solar cell based on the film with Ag/(Ag + Cu) of ca. 0.02. Electrostructural analyses of the devices suggested that the Ag-incorporated film in the device achieved reduction in the amounts of unfavorable copper on zinc antisite defects compared to the bare CZTS film. Moreover, the use of a Ag-incorporated film improved band alignment at the CdS(buffer)-CZTS interface. These alterations should also contribute to enhancement of device properties.

Photocarrier recombination dynamics of BiVO4 powders synthesized at different temperatures were studied by temperature-dependent steady-state and time-resolved photoluminescence (PL). Structural analysis indicates that BiVO4 materials synthesized at low temperatures contain mixed-phase crystals including monoclinic and tetragonal scheelite phase, showing poor photocatalytic performance. Relatively higher synthesis temperatures improve the photocatalyst efficiency by promoting the formation of single-phase monoclinic BiVO4 with larger grains. Excitation-power dependence along with temperature dependence of the PL of BiVO4 suggests that the donor-to-acceptor transitions are the dominant radiative recombination mechanism. Furthermore, hole effective lifetimes observed in PL decays were found in the order of nanoseconds, which is far behind the ideal radiative lifetime of ∼6 μs, calculated theoretically using van Roosbroeck-Shockley relation. This suggests that the photocarrier recombination in BiVO4 occurs predominately nonradiatively via multiphonon emission, plausibly through deep-level defects. In addition, the coexistence of tetragonal and monoclinic phases might indirectly induce additional trap states, leading to an increase of the nonradiative recombination rate and subsequently poor photocatalytic efficiency in samples synthesized at lower temperatures. Thus, the nonradiative recombination which is associated with a short photocarrier lifetime and small holes diffusion length is the most limiting process for BiVO4 performance.

Effects of zirconium (Zr) doping into BiVO4 powder on its structural properties and photocatalytic activity for O2 evolution were examined. The formation of BiVO4 powder crystallized in a monoclinic scheelite structure (ms-BiVO4) was achieved when the sample was doped with a relatively small amount of Zr. The photocatalytic activity of Zr-doped ms-BiVO4 powder was much higher than that of non-doped ms-BiVO4. However, further doping caused a reduction of photocatalytic activity for O2 evolution due to the occurrence of structural alterations into tetragonal scheelite and tetragonal zircon structures. Similar effects of Zr doping were also observed for the photoelectrochemical (PEC) system based on BiVO4 thin films doped with various amounts of Zr. Thus, Zr doping was confirmed to be effective for improvements of photocatalytic and PEC functions of BiVO4 for water oxidation.

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Copper antimony disulfide (CuSbS2) is a promising candidate for solar absorber material owing to its high photoabsorption property and earth-abundant constituent elements. In this study, we fabricated CuSbS2 crystals of various nonstoichiometric compositions and investigated their optical and electric properties for their applications in photovoltaic devices. Band gap energies of CuSbS2 crystals thus-obtained were almost constant (ca. 1.5 eV) irrespective of their compositions. Hall-resistivity measurements exhibited that a CuSbS2 crystal with the compositional formula of 1.03/1.00/1.86 showed the best properties among the samples prepared in this study: the resistivity, hole concentration, and mobility of the sample were 1.4 Ω cm, 6.0 × 1016 cm−3, and 7.4 cm2 V−1 s−1, respectively. Although further optimization would be expected, the obtained properties are suitable for an absorber of photovoltaics.