Evidence and Influence of Copper Vacancies in p-Type CuGaO₂ Mesoporous Films

Abstract

Delafossite CuGaO2 nanocrystals were hydrothermally synthesized and characterized spectroscopically and electrochemically as mesoporous thin films. The nanocrystals demonstrate a preferred orientation within the film structure, as shown by enhancement of the (00l) peaks via two-dimensional powder X-ray diffraction. Annealing conditions of low and high temperature (i.e., 100–300 °C), with oxygen and/or argon atmospheres, were investigated, and the resulting effect on the thin film electrochemistry was measured. Cyclic voltammetry showed an increase in non-faradaic current with higher annealing temperatures and demonstrated a quasi-reversible redox feature (E 1/2 = 0.1 V vs Fc+1/0). This feature is assigned to a CuII/CuI redox couple associated with surface defects. X-ray photoelectron and energy dispersive spectroscopies provide evidence for CuII surface defects and copper vacancies. Electrochemical impedance spectroscopy revealed that CuGaO2 films were highly conductive with σ ∼ 10–5 Ω–1 cm–1, consistent with a large density of hole carriers induced by copper vacancies. The significance of synthesis, film preparation, and annealing conditions on the presence of surface defects and large hole densities is discussed. The prevalence of such defects in delafossite CuGaO2 is expected to have a large impact on the use of this material as a hole transport layer in solar cell architectures.

Dye Anchoring on CuCrO2 Surfaces for p-Type Dye-Sensitized Solar Cell Applications: An Ab Initio Study

“…Both in ACN and water solution, indeed, the stability of the molecular monodentate adsorption mode slightly reduces due to the dielectric screening of the strong H-bond with the surface and the M-Cr H and BB-Cr–Cr configurations become isoenergetics. Inclusion of the solvent clearly also stabilizes the dissociated monodentate mode, M-Cr, presenting a dangling C–O bond.Under growth conditions of delafossites, the dominant intrinsic p-type defects are Cu + vacancies. , Therefore, in order to refine our structural model of the CuCrO 2 (012) surface and investigate the effect of native Cu vacancies on the −COOH adsorption mechanism and energetics, we created single Cu defects on the two uppermost surface layers, in proximity of the adsorbed molecule; we will hereafter refer to this surface as “reduced surface”. The presence of a single Cu + vacancy on our slab gives a defect percentage of 1.7%, which is reasonable considering the experimental value (4 ± 2%) obtained for CuGaO 2 via X-ray photoelectron spectroscopic measurements .…”

“…The presence of a single Cu + vacancy on our slab gives a defect percentage of 1.7%, which is reasonable con-sidering the experimental value (4 ± 2 %) obtained for CuGaO 2 via XPS (X-ray Photoelectron Spectroscopic) measurements. 40 A comparison between the total and partial density of states of the pristine and reduced surfaces shows that the Cu vacancy does not introduce significant intra-gap states (see Figure S3 in Supporting Information). Moreover, by looking at the difference in the Bader's charges between the clean and defective slabs (Figure S4 in Supporting Information), one can notice that the charges on the Cr atoms are only marginally changed by the presence of the defect, with a difference of charge of 0.04 electrons.…”

“…Here we tackle this issue, reporting a systematic DFT investigation of the adsorption mechanism of CH 3 –COOH and CH 3 –PO 3 H 2 on the high-index (012) CuCrO 2 surface, considering implicit solvation effects and also taking into account the impact of Cu + vacancies on the different adsorption modes as well as on their stability. In earlier studies, Cu vacancies have been discussed mainly to understand the p-type conductivity of delafossites. ,− Herein, we present Cu + vacancy point defect and highlight their importance in stabilizing BB modes.…”

“…In earlier studies, Cu vacancies have been discussed mainly to understand the p-type conductivity of delafossites. 22,[38][39][40] Herein, we present Cu + vacancy point defect and highlight their importance in stabilizing bidentate bridging (BB) modes.…”

The efficiency of short sintering time on thermoelectric properties of delafossite CuCr0:85Mg0:15O2 ceramics

“…HRTEM micrographs of CuCr 0.85 Mg 0.15 O 2 compounds, as seen in Figure2was used as a supplemental tool for the X-ray diffraction method to detect the existence of the multi-phases in the compounds. The co-existence of CuCrO 2 , MgCr 2 2 phase can clearly be observed via the grains with the face like "terraces" because the delafossite material has the layer structure[23][24][25] . Besides, for the sample prepared with low dwell time, grains with the + and Cu 2+ ion states.Besides, the appearance of a broadband located at ca.…”