Quantum-Confined CdTe Films Deposited by SILAR and Their Photoelectrochemical Stability in the Presence of Se^2– as a Hole Scavenger

Quantum-confined CdTe films were deposited by successive ionic layer adsorption and reaction (SILAR) on nc-TiO₂ and on a conducting oxide electrode (FTO) from aqueous solutions of Cd²⁺ and Te^2– prepared in situ under inert atmosphere. The films were characterized with UV–visible absorption, SEM, EDX, and XRD. CdTe_<i>n</i> films exhibited a zinc-blende structure and a red-shift in absorbance with increasing SILAR cycles (<i>n</i>) consistent with quantum size effects and featured either a mesoporous morphology on FTO or followed the contours of the titania nanoparticles on nc-TiO₂ films. The films’ photoelectrochemical behavior was studied in the presence of Se^2– compared to S^2– as hole scavengers. The incident-photon-to-current conversion efficiency reached ca. 16% at 460 nm and 9% at 500 nm at CdTe₁₀/nc-TiO₂ in alkaline Se^2– electrolyte compared to 1% at 460 nm or 0.5% at 500 nm in S^2–. CdTe₁₀ films examined after acquiring a photoaction spectrum in Se^2– still exhibited zinc-blende structure, EDX analysis showed Cd and Te peaks and no detectable Se, and the absorbance slightly increased with films remaining red-black. On the other hand, the absorbance edge and photocurrent onset shifted significantly to the blue and the films became yellow during the same measurement in S^2–, indicating dissolution and formation of CdS, consistent with reports for CdTe single crystals and Q-CdTe. After hours of illumination at 500 nm at −0.55 V in Se^2–, Se became incorporated in the films; however, the photocurrent decreased by only 5–8% after 2–3 h illumination, indicating significant photoelectrochemical stability. The results are attributed to effective quenching of the anodic dissolution of CdTe by Se^2– scavenging the hole, and a slow growth of a protective overlayer possibly of CdTe_1–<i>x</i>Se_<i>x</i> that does not block photocurrent generation, in contrast to the behavior of CdTe in sulfide electrolyte

Amplification in Light Energy Conversion at Q‑CdTe Sensitized TiO₂ Photonic Crystal, Photoelectrochemical Stability in Se^2– Electrolyte, and Size-Dependent Type II Q‑CdTe/CdSe Formation

This study investigates the ability of Se^2– redox electrolyte to separate the photoholes and stabilize Q-CdTe quantum dot solar cell with a liquid junction. We examined the photophysical and photoelectrochemical behaviors of Q-CdTe in two sizes, green-emitting dots of 2.3–2.7 nm diameter and red-emitting dots of 4 nm diameter, in the presence of alkaline Se^2– electrolyte prepared under inert atmosphere. Photoelectrochemical, absorbance, emission and emission quenching measurements revealed the presence of size dependence in Se^2– surface binding to Q-CdTe, growth of type II Q-CdTe/CdSe, and stability in the photoelectrochemical cell. Emission quenching measurements show that Se^2– scavenges the Q-CdTe photohole, with mechanisms that depended on size and quencher concentration. Binding of Se^2– to green-emitting Q-CdTe occurred with a greater binding constant compared to the red-emitting dots, resulting in formation of type II Q-CdTe/CdSe at the smaller core indicated in red-shifted absorbance and emission spectra with incremental Se^2– addition at room temperature. Photoelectrochemical measurements acquired at Q-CdTe sensitized nc-TiO₂ and TiO₂ inverse opal with a stop band at 600 nm, 600-i-TiO₂-o, in Se^2– electrolyte confirmed this redox species ability to scavenge the photohole and to protect Q-CdTe against fast photoanodic dissolution, with greater stability observed for the larger dots. Gains in the photon-to-current conversion efficiency attributed to light trapping were measured at Q-CdTe sensitized 600-i-TiO₂-o relative to nc-TiO₂

Yttrium Tantalum Oxynitride Multiphases as Photoanodes for Water Oxidation

The perovskite yttrium tantalum oxynitride is theoretically proposed as a promising semiconductor for solar water splitting because of the predicted band gap and energy positions of band edges. In experiments, however, we show here that depending on the processing parameters, yttrium tantalum oxynitrides exist in multi phases, including the desired perovskite YTaON2, defect fluorite YTa(O,N,square)(4), and N-doped YTaO4. These multiphases have band gaps ranging between 2.13 and 2.31 eV, all responsive to visible light. The N-doped YTaO4, perovskite main phase, and fluorite main phase derived from crystalline fergusonite oxide precursors exhibit interesting photoelectrochemical performances for water oxidation, while the defect fluorite derived from low-crystallized scheelite-type oxide precursors shows negligible activity. Preliminary measurements show that loading an IrOx, cocatalyst on N-doped YTaO4 significantly improves its photoelectrochemical performance, encouraging further studies to optimize this new material for solar fuel production

Black-Si as a Photoelectrode

The fabrication and characterization of photoanodes based on black-Si (b-Si) are presented using a photoelectrochemical cell in NaOH solution. B-Si was fabricated by maskless dry plasma etching and was conformally coated by tens-of-nm of TiO2 using atomic layer deposition (ALD) with a top layer of CoO x cocatalyst deposited by pulsed laser deposition (PLD). Low reflectivity R &lt; 5 % of b-Si over the entire visible and near-IR ( &lambda; &lt; 2 &nbsp; &mu; m) spectral range was favorable for the better absorption of light, while an increased surface area facilitated larger current densities. The photoelectrochemical performance of the heterostructured b-Si photoanode is discussed in terms of the n-n junction between b-Si and TiO2