Managing Photoinduced Electron Transfer in AgInS2-CdS Heterostructures

AgInS2-Embedded Photocatalytic Membrane: Insights into the Excited State and Electron Transfer Dynamics

Photocatalytic reactions at semiconductor nanocrystal surfaces are useful for synthesizing value-added chemicals using sunlight. Semiconductor nanocrystals dispersed in a rigid framework, such as polymer film, can mitigate issues such as aggregation, product separation, and other challenges that are usually encountered in suspensions or slurries. Using a cation exchange technique, we successfully embedded AgInS2 nanoparticles into a Nafion matrix, termed AgInS2-Nafion. This was achieved through a galvanic exchange between In and Ag in In2S3 present within the Nafion film, enabling an adjustable Ag:In ratio for optimized photophysical properties. As in the case of colloidal suspension, the AgInS2 particles embedded in Nafion exhibit a long absorption tail, a broad emission band with a large Stokes shift, and emission lifetimes extending into the microseconds that are characteristic of donor-acceptor pairs, DAP. Remediation of surface states with the treatment of 3-mercaptopropionic acid resulted in significant enhancement in the emission yield. Charge carrier generation through bandgap excitation as well as activation of DAP states which reside within the bandgap is probed through transient absorption spectroscopy. The photocatalytic activity of AgInS2-Nafion was probed by using thionine as an electron acceptor. The electron transfer rate constant from excited AgInS2 to thionine as observed from transient absorption spectroscopy was determined to be ∼6.3 × 1010 s-1. The design of a photoactive membrane offers new ways to carry out photocatalytic processes with greater selectivity.

Enhanced Stability and Highly Bright Electroluminescence of AgInZnS/CdS/ZnS Quantum Dots through Complete Isolation of Core and Shell via a CdS Interlayer

An approach for synthesizing AgInZnS/CdS/ZnS core-shell-shell quantum dots (QDs) that demonstrate exceptional stability and electroluminescence (EL) performance is introduced. This approach involves incorporating a cadmium sulfide (CdS) interlayer between an AgInZnS (AIZS) core and a zinc sulfide (ZnS) shell to prevent the diffusion of Zn ions into the AIZS core and the cation exchange at the core-shell interface. Consequently, a uniform and thick ZnS shell, with a thickness of 2.9 nm, is formed, which significantly enhances the stability and increases the photoluminescence quantum yield (87.5%) of the QDs. The potential for AIZS/CdS/ZnS QDs in electroluminescent devices is evaluated, and an external quantum efficiency of 9.6% in the 645 nm is achieved. These findings highlight the importance of uniform and thick ZnS shells in improving the stability and EL performance of QDs.

AgIn5S8/ZnS Quantum Dots for Luminescent Down-Shifting and Antireflective Layer in Enhancing Photovoltaic Performance

Colloidal AgIn5S8/ZnS quantum dots (QDs) have recently emerged as a promising, efficient, nontoxic, down-shifting material in optoelectronic devices. These QDs exhibit a high photoluminescent quantum yield and offer a range of potential applications, specifically in the field of photovoltaics (PVs) for light management. In this work, we report an eco-friendly method to synthesize AgIn5S8/ZnS QDs and deposit them on commercial silicon solar cells (with an active area of 7.5 cm2), with which the short-circuit current (JSC) enhanced by 1.44% and hence the power conversion efficiency by 2.51%. The enhancements in PV performance are mainly attributable to the improved external quantum efficiency in the ultraviolet region and reduced surface reflectance in the ultraviolet and near-infrared regions. We study the effect of QD concentration on the bifunctions of downshifting and antireflection. The optimal 15 mg/mL QDs blade-coated onto the Si solar cells realize maximum current generation as the reflectance loss in the visible wavelength is compensated by the minimized reflection in the near-infrared region.

Photoinduced electron transfer across the polymer-capped CsPbBr3 interface in a polar medium

In-situ polymer capping of cesium lead bromide (CsPbBr₃) nanocrystals with polymethyl acrylate is an effective approach to improve the colloidal stability in the polar medium and thus extends their use in photocatalysis. The photoinduced electron transfer properties of polymethyl acrylate (PMA)-capped CsPbBr₃ nanocrystals have been probed using surface-bound viologen molecules with different alkyl chains as electron acceptors. The apparent association constant (K_app) obtained for the binding of viologen molecules with PMA-capped CsPbBr₃ was 2.3 × 10⁷ M^-1, which is an order of magnitude greater than that obtained with oleic acid/oleylamine-capped CsPbBr₃. Although the length of the alkyl chain of the viologen molecule did not show any impact on the electron transfer rate constant, it influenced the charge separation efficiency and net electron transfer quantum yield. Viologen moieties with a shorter alkyl chain length exhibited a charge separation efficiency of 72% compared with 50% for the longer chain alkyl chain length viologens. Implications of polymer-capped CsPbBr₃ perovskite nanocrystals for carrying out photocatalytic reduction in the polar medium are discussed.