We present a measurement of the energies and capture cross-sections of defect states in methylammonium lead bromide (MAPbBr₃) single crystals. Using Laplace current deep level transient spectroscopy (I-DLTS), two prominent defects were observed with energies 0.17 eV and 0.20 eV from the band edges, and further I-DLTS measurements confirmed that these two defects are bulk defects. These results show qualitative agreement with theoretical predictions, whereby all of the observed defects behave as traps rather than as generation-recombination centers. These results provide one explanation for the high efficiencies and open-circuit voltages obtained from devices made with lead halide perovskites.

Copper (II) oxide (CuO) nanostructures were prepared on fluorine-doped tin oxide (FTO) using a three-step heat treatment process in a sol–gel dip-coating method. The precursor used for the dip-coating process was prepared using copper acetate, propan-2-ol, diethanolamine, and polyethylene glycol 400. Dip-coated films in layers of 2, 4, 6, 8, and 10 were prepared by drying each layer at 110 and 250 °C for 10 and 5 min, respectively, followed by calcination at 550 °C for 1 h. The films were applied toward photocatalytic hydrogen evolution from water. The X-ray diffraction (XRD) pattern of the films confirmed the tenorite phase of pure CuO. Raman spectroscopy revealed the 1A_g and 2B_g phonon modes of CuO, confirming the high purity of the films produced. The CuO films absorb significant photons in the visible spectrum due to their low optical band gap of 1.25–1.33 eV. The highest photocurrent of −2.0 mA/cm² at 0.45 V vs reversible hydrogen electrode (RHE) was recorded for CuO films consisting of six layers under 1 sun illumination. A more porous surface, low charge transfer resistance, and high double-layer capacitance at the CuO/electrolyte interface observed for the films consisting of six layers contributed to the high photocurrent density attained by the films. CuO films consisting of six layers prepared using the conventional two-step heat treatment process for comparative purposes yielded 65.0% less photocurrent at 0.45 V vs RHE compared to similar films fabricated via the three-step heating method. The photocurrent response of the CuO nanostructures prepared using the three-step heat treatment process is promising and can be employed for making CuO for photovoltaic and optoelectronic applications.

In this research, three different sets of hematite (α-Fe₂O₃) films of various thicknesses were prepared using dip, spin, and combined dip/spin coating methods. α-Fe₂O₃films of 450–500, 740–800 and 920–980 ± 30 nm thicknesses were prepared using each of the coating methods, and their photoelectrochemical (PEC) behaviour was investigated. Dip coated films produced the best photoresponse while the films prepared using the spin coating method yielded the least photocurrent values across films of different thicknesses. Maximum photocurrent densities of 34.6, 7.8, and 13.5 μA/cm²V vs reversible hydrogen electrode (RHE) were obtained for the dip, spin and combined dip/spin coated films with a thickness of 740–800 ± 30 nm respectively. Improved crystallization, low charge transfer resistance at the α-Fe₂O₃/electrolyte interface, high surface states capacitance and the more negative flat band potential values obtained for dip coated films have been associated with the enhanced photocurrent response recorded for the films. The preferential crystal growth of spin coated films in the (104) plane associated with low electron mobility and the high resistance to charge transfer at the α-Fe₂O₃/electrolyte interface of the films is largely responsible for their low photoresponse. This study underscores the significance of simultaneously optimizing both coating techniques for film deposition and the film’s thickness in preparing nanostructured α-Fe₂O₃films for PEC applications.

In this work, we report the effect of zinc (Zn) and nickel (Ni) co-doping of hydrothermally synthesized hematite nanorods prepared on fluorine-doped tin oxide (FTO) substrates for enhanced photoelectrochemical (PEC) water splitting. Seeded hematite nanorods (NRs) were facilely doped with a fixed concentration of 3 mM Zn and varied concentrations of 0, 3, 5, 7, and 9 mM Ni. The samples were observed to have a largely uniform morphology of vertically aligned NRs with slight inclinations. The samples showed high photon absorption within the visible spectrum due to their bandgaps, which ranged between 1.9–2.2 eV. The highest photocurrent density of 0.072 mA/cm² at 1.5 V vs. a reversible hydrogen electrode (RHE) was realized for the 3 mM Zn/7 mM Ni NRs sample. This photocurrent was 279% higher compared to the value observed for pristine hematite NRs. The Mott–Schottky results reveal an increase in donor density values with increasing Ni dopant concentration. The 3 mM Zn/7 mM Ni NRs sample produced the highest donor concentration of 2.89 × 10¹⁹ (cm⁻³), which was 2.1 times higher than that of pristine hematite. This work demonstrates the role of Zn and Ni co-dopants in enhancing the photocatalytic water oxidation of hematite nanorods for the generation of hydrogen.

In this study, zinc-doped ($\alpha$-Fe${}_2$O${}_3$:Zn), silver-doped ($\alpha$-Fe${}_2$O${}_3$:Ag) and zinc/silver co-doped hematite ($\alpha$-Fe${}_2$O${}_3$:Zn/Ag) nanostructures were synthesized by spray pyrolysis. The synthesized nanostructures were used as photoanodes in the photoelectrochemical (PEC) cell for water-splitting. A significant improvement in photocurrent density of 0.470 mAcm${}^{-2}$ at 1.23 V vs. reversible hydrogen electrode (RHE) was recorded for $\alpha$-Fe${}_2$O${}_3$:Zn/Ag. The $\alpha$-Fe${}_2$O${}_3$:Ag, $\alpha$-Fe${}_2$O${}_3$:Zn and pristine hematite samples produced photocurrent densities of 0.270, 0.160, and 0.033 mAcm${}^{-2}$, respectively. Mott–Schottky analysis showed that $\alpha$-Fe${}_2$O${}_3$:Zn/Ag had the highest free carrier density of 8.75 × 10${}^{20}$ cm${}^{-3}$, while pristine $\alpha$-Fe${}_2$O${}_3$, $\alpha$-Fe${}_2$O${}_3$:Zn, $\alpha$-Fe${}_2$O${}_3$:Ag had carrier densities of 1.57 × 10${}^{19}$, 5.63 × 10${}^{20}$, and 6.91 × 10${}^{20}$ cm${}^{-3}$, respectively. Electrochemical impedance spectra revealed a low impedance for $\alpha$-Fe${}_2$O${}_3$:Zn/Ag. X-ray diffraction confirmed the rhombohedral corundum structure of hematite. Scanning electron microscopy micrographs, on the other hand, showed uniformly distributed grains with an average size of <30 nm. The films were absorbing in the visible region with an absorption onset ranging from 652 to 590 nm, corresponding to a bandgap range of 1.9 to 2.1 eV. Global analysis of ultrafast transient absorption spectroscopy data revealed four decay lifetimes, with a reduction in the electron-hole recombination rate of the doped samples on a timescale of tens of picoseconds.