Spectroelectrochemical insights into the intrinsic nature of lead halide perovskites.

Lead halide perovskites have emerged as a new class of semiconductor materials with exceptional optoelectronic properties, sparking significant research interest in photovoltaics and light-emitting diodes. However, achieving long-term operational stability remains a critical hurdle. The soft, ionic nature of the halide perovskite lattice renders them vulnerable to various instabilities.

Anion-Driven Bandgap Tuning of AgIn(SSe) Quantum Dots.

Accurate tuning of the electronic and photophysical properties of quantum dots is required to maximize the light conversion efficiencies in semiconductor-assisted processes. Herein, we report a facile synthetic procedure for AgIn(SSe) quantum dots with S content () ranging from 1 to 0. This simple approach allowed us to tune the bandgap (2.

Demystifying Triplet-Triplet Annihilation Mechanism in the CsPbI-Rubrene-DBP Upconversion System.

A triplet-triplet annihilation-based upconversion (TTA-UC) system, employing a multichromophore assembly, is convenient to harvest low-energy photons for light energy conversion and optoelectronic applications. The primary donor in the TTA-UC system, typically a low-bandgap semiconductor, captures the low-energy photons and transfers triplet energy to an annihilator dye molecule, which in turn generates a high-energy singlet excited state via T-T annihilation. We have now succeeded in revealing kinetic and mechanistic details of multistep energy transfer processes in the CsPbI-rubrene-perylene derivative (DBP) films by analyzing time-resolved emission and absorption measurements.

Charge Transfer Kinetics in Halide Perovskites: On the Constraints of Time-Resolved Spectroscopy Measurements.

Understanding photophysical processes in lead halide perovskites is an important aspect of optimizing the performance of optoelectronic devices. The determination of exact charge carrier extraction rate constants remains elusive, as there is a large and persistent discrepancy in the reported absolute values. In this review, we concentrate on experimental procedures adopted in the literature to obtain kinetic estimates of charge transfer processes and limitations imposed by the spectroscopy technique employed.

From Light to Dark: Dancing with Electrons in Colloidal 2D MoS Nanosheets.

Extending the lifetime of photogenerated electrons in semiconductor systems is an important criterion for the conversion of light into storable energy. We have now succeeded in storing electrons in a photoirradiated colloidal molybdenum disulfide (MoS) suspension, showcasing its unique reversible photoresponsive behavior. The dampened A and B excitonic peaks indicate the accumulation of photogenerated electrons and the minimization of interactions between MoS interlayers.

Tuning Energy Transfer Pathways in Halide Perovskite-Dye Hybrids through Bandgap Engineering.

Lead halide perovskite nanocrystals, which offer rich photochemistry, have the potential to capture photons over a wide range of the visible and infrared spectrum for photocatalytic, optoelectronic, and photon conversion applications. Energy transfer from the perovskite nanocrystal to an acceptor dye in the form of a triplet or singlet state offers additional opportunities to tune the properties of the semiconductor-dye hybrid and extend excited-state lifetimes. We have now successfully established the key factors that dictate triplet energy transfer between excited CsPbI and surface-bound rhodamine dyes using absorption and emission spectroscopies.

Extending Infrared Emission via Energy Transfer in a CsPbI-Cyanine Dye Hybrid.

Directing energy flow in light harvesting assemblies of nanocrystal-chromophore hybrid systems requires a better understanding of factors that dictate excited-state processes. In this study, we explore excited-state interactions within the CsPbI-cyanine dye (IR125) hybrid assembly through a comprehensive set of steady-state and time-resolved absorption and photoluminescence (PL) experiments. Our photoluminescence investigations reveal the quenching of CsPbI emission alongside the simultaneous enhancement of IR125 fluorescence, providing evidence for a singlet energy transfer.

AgInS-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 AgInS nanoparticles into a Nafion matrix, termed AgInS-Nafion.

Trap or Triplet? Excited-State Interactions in 2D Perovskite Colloids with Chromophoric Cations.

Movement of energy within light-harvesting assemblies is typically carried out with separately synthesized donor and acceptor species, which are then brought together to induce an interaction. Recently, two-dimensional (2D) lead halide perovskites have gained interest for their ability to accommodate and assemble chromophoric molecules within their lattice, creating hybrid organic-inorganic compositions. Using a combination of steady-state and time-resolved absorption and emission spectroscopy, we have now succeeded in establishing the competition between energy transfer and charge trapping in 2D halide perovskite colloids containing naphthalene-derived cations (i.

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

In-situ polymer capping of cesium lead bromide (CsPbBr) 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 CsPbBr nanocrystals have been probed using surface-bound viologen molecules with different alkyl chains as electron acceptors. The apparent association constant (K) obtained for the binding of viologen molecules with PMA-capped CsPbBr was 2.

How Pendant Groups Dictate Energy and Electron Transfer in Perovskite-Rhodamine Light Harvesting Assemblies.

Energy and electron transfer processes allow for efficient manipulation of excited states within light harvesting assemblies for photocatalytic and optoelectronic applications. We have now successfully probed the influence of acceptor pendant group functionalization on the energy and electron transfer between CsPbBr perovskite nanocrystals and three rhodamine-based acceptor molecules. The three acceptors─rhodamine B (RhB), rhodamine isothiocyanate (RhB-NCS), and rose Bengal (RoseB)─contain an increasing degree of pendant group functionalization that affects their native excited state properties.

Enhanced Charge Carrier Separation in WO/BiVO Photoanodes Achieved via Light Absorption in the BiVO Layer.

Photoelectrochemical (PEC) water splitting converts solar light and water into oxygen and energy-rich hydrogen. WO/BiVO heterojunction photoanodes perform much better than the separate oxide components, though internal charge recombination undermines their PEC performance when both oxides absorb light. Here we exploit the BiVO layer to sensitize WO to visible light and shield it from direct photoexcitation to overcome this efficiency loss.

Excited State and Transient Chemistry of a Perylene Derivative (DBP). An Untold Story.

Transient chemistry of sensitizing dyes is important to obtain insights into the photochemical conversion processes of light harvesting assemblies. We have now employed transient absorption spectroscopy (pulsed laser and pulse radiolysis) to characterize the excited state and radical intermediates of a perylene derivative, (5,10,15,20-Tetraphenylbisbenz[5,6]indeno[1,2,3-:1',2',3'-]perylene (DBP). The distinguishable transient absorption features for the singlet and triplet excited states and radical anion and radical cation provide spectral fingerprints to identify the reaction intermediates in photochemical energy and electron transfer processes of composite systems involving DBP.

Excited-State Transient Chemistry of Rubrene: A Whole Story.

The ability to manipulate low-energy triplet excited states into higher-energy emissive singlet states, a process known as photon upconversion (UC), has potential applications in bioimaging, photocatalysis, and in increasing the efficiency of solar cells. However, the overall UC mechanism is complex and can involve many intermediate states, especially when semiconductors such as lead halide perovskites are used to sensitize the required triplet states. Using a combination of pulse radiolytic and electrochemical techniques, we have now explored the transient features of rubrene─a commonly employed triplet annihilator in UC systems.

Energy Electron Transfer: Managing Excited-State Interactions in Perovskite Nanocrystal-Molecular Hybrids.

Energy and electron transfer processes in light harvesting assemblies dictate the outcome of the overall light energy conversion process. Halide perovskite nanocrystals such as CsPbBr with relatively high emission yield and strong light absorption can transfer singlet and triplet energy to surface-bound acceptor molecules. They can also induce photocatalytic reduction and oxidation by selectively transferring electrons and holes across the nanocrystal interface.

Managing photoinduced electron transfer in AgInS-CdS heterostructures.

Ternary semiconductors such as AgInS, with their interesting photocatalytic properties, can serve as building blocks to design light harvesting assemblies. The intraband transitions created by the metal ions extend the absorption well beyond the bandgap transition. The interfacial electron transfer of AgInS with surface bound ethyl viologen under bandgap and sub-bandgap irradiation as probed by steady state photolysis and transient absorption spectroscopy offers new insights into the participation of conduction band and trapped electrons.

Photoinduced Transformation of CsAuBr into CsPbBr Nanocrystals.

Lead-free halide double perovskites offer an environmentally friendly alternative to lead halide perovskites for designing optoelectronic solar cell devices. One simple approach to synthesize such double halide perovskites is through metal ion exchange. CsPbBr nanocrystals undergo exchange of Pb with Au(I)/Au(III) to form double perovskite CsAuBr.

CsPbBr-CdS heterostructure: stabilizing perovskite nanocrystals for photocatalysis.

The instability of cesium lead bromide (CsPbBr) nanocrystals (NCs) in polar solvents has hampered their use in photocatalysis. We have now succeeded in synthesizing CsPbBr-CdS heterostructures with improved stability and photocatalytic performance. While the CdS deposition provides solvent stability, the parent CsPbBr in the heterostructure harvests photons to generate charge carriers.

A Bipolar CdS/Pd Photocatalytic Membrane for Selective Segregation of Reduction and Oxidation Processes.

A photocatalytically active bipolar membrane consisting of a CdS photocatalyst and Pd electrocatalyst has been constructed to carry out environmentally relevant oxidation and reduction processes. The ion exchange property of a bipolar membrane (BPM) has allowed us to load the CdS photocatalyst on one side and Pd electrocatalyst on the other side. By inserting the photocatalytic BPM-CdS/Pd membrane between the two compartments of an H-cell, we can separate the reduction and oxidation processes.