No abstract

A facile interfacial charge transfer (CT) with a reduced inter-layer energy band regulates the charge transport mechanism in any optoelectronic device. The enhancement in semiconductor-based device performance often demands improved CT dynamics and collection of free carriers with reduced charge recombination. In this work, we present a detailed inspection of the photo-induced CT between inorganic lead halide perovskite nanocrystals (PNCs) with varied compositions and their consequence on the charge transport process. The superior CT rate in mixed halide CsPbBr2Cl PNCs with naphthoquinone (NPQ) is revealed when compared with the parent CsPbBr3 PNCs and its anion-exchanged counterpart CsPbCl3. The glimpses of hole transfer contribution along with electron transfer are detected for CsPbBr2Cl with superior CT efficiency. The enhanced conduction current after the insertion of NPQ into the PNCs with a reduced hysteresis suggests an improved charge transport in the fabricated device compared to the pristine PNCs. These findings can contribute to a better understanding of multiple ways of engineering optoelectronic devices to boost performance and efficiencies and the concurrent role of the CT process in the conduction mechanism.

Photoinduced electron transfer (PET) is a widely studied phenomenon in nanoscale carbon dots (CDs) due to the availability of free electrons on their surfaces. It is often treated as a molecular ruler to understand the interaction between nearby donor and acceptor pairs. The current report highlights the modulation of the electron transfer (ET) process in redox-treated CDs with an acceptor molecule, menadione (MD), when subjected to a microemulsion method. In the presence of cationic CTAB micellar heterogeneity, the ET kinetics get markedly altered due to the controlled diffusion dynamics of the reactant inside the microemulsion. In CTAB micellar media, reduced CDs (RCDs) show a higher ET efficiency with MD compared to the oxidized CDs (OCDs), owing to the substantial change in their surface charge and the stronger Coulombic interaction with the micellar interface. Moreover, the presence of CTAB moieties with RCDs greatly influences the local conductance and the electrical band gap at the single molecular level as noticed from current sensing atomic force microscopy measurements compared to OCDs. The current−voltage (I−V) measurements are observed to be nonlinear, revealing both direct and Fowler−Nordheim (FN) types of tunneling, while the presence of MD abruptly enhances the conductance linearly, curtailing the FN tunneling.

Regulated excited state energy and charge transfer play a pivotal role in nanoscale semiconductor device performance for efficient energy harvesting and optoelectronic applications. Herein, we report the influence of Forster resonance energy transfer (FRET) on the excited-state dynamics and charge transport properties of metal halide perovskite nanocrystals (PNCs), CsPbBr 3 , and its anion-exchanged counterpart CsPbCl 3 with CdSe/ZnS quantum dots (QDs). We report a drop in the FRET efficiency from ∼85% (CsPbBr 3 ) to ∼5% (CsPbCl 3 ) with QDs, inviting significant alteration in their charge transport properties. Using two-probe measurements we report substantial enhancement in the current for the blend structure of PNCs with QDs, originating from the reduced trap sites, compared to that of the pristine PNCs. The FRET-based upshot in the conduction mechanism with features of negative differential resistance and negligible hysteresis for CsPbBr 3 PNCs can add new directions to high performance-based photovoltaics and optoelectronics.

Due to their uniqueness in tunable photophysics, transition metal dichalcogenide (TMD) based quantum dots (QDs) have emerged as the next-generation quantum materials for technology-based semiconductor applications. This demands frontline research on the rational synthesis of the TMD QDs with controlled shape, size, nature of charge migration at the interface, and their easy integration in optoelectronic devices. In this article, with a controlled solution-processed synthesis of MoS 2 and WS 2 QDs, we demonstrate the disparity in their structural, optical, and electrical characteristics in bulk and confinement. With a series of steady-state and time-resolved spectroscopic measurements in different media, we explore the uncommon photophysics of MoS 2 and WS 2 QDs such as excitation-dependent photoluminescence and assess their excited state charge transfer kinetics with a redox-active biomolecule, menadione (MQ). In comparison to the homogeneous aqueous medium, photoinduced charge transfer between the QDs and MQ becomes more plausible in encapsulated cetyltrimethylammonium bromide (CTAB) micelles. Current sensing atomic force microscopy (CS-AFM) measurements at a single molecular level reveal that the facilitated charge transfer of QDs with MQ strongly correlates with an enhancement in their charge transport behavior. An increase in charge transport further depends on the density of states of the QDs directing a change in Schottky emission to Fowler−Nordheim (FN) type of tunneling across the metal−QD−metal junction. The selective response of the TMD QDs while in proximity to external molecules can be used to design advanced optoelectronic devices and applications involving rectifiers and tunnel diodes for future quantum technology.