Intrinsic Acceptor-like Defects and Their Effect on Carrier Transport in Polycrystalline Cu₂O Photocathodes

The disparity between theoretical estimate and experimentally achieved efficiency of Cu2O-based photovoltaic and photoelectrochemical devices is attributed to poor electrical transport in the material. Toward this, we study native point defects in single and polycrystalline Cu2O and their effect on charge carrier transport via temperature-dependent Hall measurement in a temperature range of 82–300 K. The temperature-dependent carrier concentration evinces the presence of two monovalent acceptors pertaining to VCu and VCusplit. We find that the second acceptor level lies ∼80 meV above the first acceptor and is active above ∼200 K temperatures only. Interestingly, the compensation ratio (ND/NA) decreases with the grain boundary cross section (ΛGB) of the sample, from 0.07 for the sample with ΛGB = 0.45 ×10–3 μm–1 to 0.02 for the sample with ΛGB = 0.22 × 10–3μm–1. In polycrystalline samples, carrier scattering at grain boundaries governs the hole transport at low temperatures (T < 150 K). However, trapping of holes by the acceptor-like intrinsic defects is the major factor affecting the high-temperature mobility in both single and polycrystalline Cu2O

Origin of the Catalytic Activity Improvement of Electrochemically Treated Carbon: An Electrical and Electrochemical Investigation

Improvement in catalytic activity of electrochemically treated carbon (relative to the untreated carbon) toward various redox reactions is widely reported in the literature. In this work, the origin of such activity enhancement due to electrochemical treatment in a 1 M H2SO4 electrolyte in a potential range of 1–2.5 V is investigated using physical, electrical, and electrochemical methods. The physical characterizations suggest intercalation of anions (bisulfate) between the graphite layers from the H2SO4 electrolyte. Electrical characterizations (both Hall measurement and Mott–Schottky analysis) show that the samples switch from n-type to p-type behavior upon electrochemical treatment. The improvement in the catalytic activity on electrochemical treatment of carbon is explained on the basis of the change in surface characteristics, carrier concentration (ND), and active site density. The same is validated with oxygen reduction reaction in alkaline media

Atomic Layer Deposition of Transparent and Conducting p‑Type Cu(I) Incorporated ZnS Thin Films: Unravelling the Role of Compositional Heterogeneity on Optical and Carrier Transport Properties

Optically transparent and highly conducting p-type Cu­(I) incorporated ZnS (Cu:ZnS) films are deposited by stacking individual layers of CuS and ZnS using atomic layer deposition. The deposition chemistry and growth mechanism are studied by in situ quartz crystal microbalance. Compositional disorder in atomic scale is observed with increasing Cu incorporation in the films that results in systematic decrease in the optical transmittance in the visible spectrum. Again the conductivity also emphatically depends on the volume fraction of phase-segregated conducting covellite phase. An illustrious correlation prevailing the interplay between the optical transparency and the charge transport mechanism is established. The hole transport mechanism that indicates insulator-to-metal transition with increasing Cu incorporation in the composite is explained in terms of an inhomogeneously disordered system. Under optimized conditions, the material having moderately high optical transmission with degenerate carrier concentration lies exactly at the confluence between the metallic and insulating regime. The lowest resistivity that is obtained here (1.3 × 10^–3 Ω cm) with >90% (after reflection correction) transmission is highly comparable to the best ones that are reported in the field and probably analogous to the commercially available n-type transparent conductors

Synthesis of CZTS/Se and Their Solid Solution from Electrodeposited Cu–Sn–Zn Metal Precursor: A Study of S and Se Replacement Reaction

Selenization, sulfurization, and sulfo-selenization of electrodeposited metal precursor (Cu–Sn–Zn) at high temperature (500–600 °C) in S, Se, or S + Se (mixed) atmospheres are used to understand the thermodynamics of chalcogenide incorporation reaction. Phase-pure CZTSe and CZTS were obtained after annealing at 500 °C for 1 min in Se (selenization) and 600 °C for 10 min in S (sulfurization) atmospheres, respectively. CZTSSe solid solutions are synthesized by the sequential annealing of metal precursors in S and Se atmosphere separately or in the mixed (S + Se) atmosphere. In the S-rich mixed atmosphere, S-rich CZTSSe solid solution is formed at all annealing conditions. Surprisingly, in a Se-rich mixed atmosphere, longer annealing at 600 °C yields S-rich CZTSSe. The CZTSSe film formed by annealing in near equimolar S/Se atmosphere exhibits a compositional gradient across the thickness. These results suggest that the crystallinity, composition, and hence the bandgap of CZTSSe can be precisely controlled by the proper choice of annealing temperature, duration, and atmosphere