Enabling Förster Resonance Energy Transfer from Large Nanocrystals through Energy Migration

The stringent distance dependence of Förster resonance energy transfer (FRET) has limited the ability of an energy donor to donate excitation energy to an acceptor over a Förster critical distance (<i>R</i>₀) of 2–6 nm. This poses a fundamental size constraint (<8 nm or ∼4<i>R</i>₀) for experimentation requiring particle-based energy donors. Here, we describe a spatial distribution function model and theoretically validate that the particle size constraint can be mitigated through coupling FRET with a resonant energy migration process. By combining excitation energy migration and surface trapping, we demonstrate experimentally an over 600-fold enhancement over acceptor emission for large nanocrystals (30 nm or ∼15<i>R</i>₀) with surface-anchored molecular acceptors. Our work shows that the migration-coupled approach can dramatically improve sensitivity in FRET-limited measurement, with potential applications ranging from facile photochemical synthesis to biological sensing and imaging at the single-molecule level

High-Performance Exciplex-Type Host for Multicolor Phosphorescent Organic Light-Emitting Diodes with Low Turn-On Voltages

Rational design and selection of suitable donor and acceptor components for optimal thermally activated delayed fluorescence (TADF) exciplex-type emitters or hosts is presently challenging. Here, we constructed successfully a blue-emitting bulk exciplex system with efficient TADF emission and high triplet energy (<i>E</i>_T) based on a donor of 4,4′,4′′-tris [3-methylphenyl­(phenyl)­amino]­triphenylamine and an acceptor of 1,3,5-tri (m-pyrid-3-yl-phenyl)­benzene. Systematic experimental and theoretical studies show that the matched frontier orbital energy levels, high <i>E</i>_T, facile intersystem crossing, high oscillator strength of the exciplex, and efficient energy transfer channels should be the main considerations during the design of high-performance exciplex-type TADF emitters and bipolar host materials. Therefore, this bulk exciplex system can behave not only as blue emitters for organic light-emitting diodes (OLEDs) but also as universal hosts for the green, yellow, and red phosphorescent OLEDs (PhOLEDs). Impressively, even under a very low guest doping level of 2 wt %, the PhOLEDs exhibit very low turn-on voltages (∼2.2 V) and high maximum external quantum efficiencies up to 18.5%. These promising device results, along with the theoretical understandings, could shed important light on the rational design of exciplex systems and their applications as either TADF emitters or bipolar host materials for high-performance and low-cost OLEDs

Synthesis of 1,3-Azaphospholes with Pyrrolo[1,2‑<i>a</i>]quinoline Skeleton and Their Optical Applications

A facile synthesis of 1,3-azaphospholes with a pyrrolo­[1,2-<i>a</i>]­quinoline skeleton has been described. These new annulated 1,3-azaphospholes exhibit good photoelectric performance and can be used as the emitting dopant in organic light-emitting diodes (OLEDs) and dye for bioimaging

Achieving Optimal Self-Adaptivity for Dynamic Tuning of Organic Semiconductors through Resonance Engineering

Current static-state explorations of organic semiconductors for optimal material properties and device performance are hindered by limited insights into the dynamically changed molecular states and charge transport and energy transfer processes upon device operation. Here, we propose a simple yet successful strategy, resonance variation-based dynamic adaptation (RVDA), to realize optimized self-adaptive properties in donor–resonance–acceptor molecules by engineering the resonance variation for dynamic tuning of organic semiconductors. Organic light-emitting diodes hosted by these RVDA materials exhibit remarkably high performance, with external quantum efficiencies up to 21.7% and favorable device stability. Our approach, which supports simultaneous realization of dynamically adapted and selectively enhanced properties via resonance engineering, illustrates a feasible design map for the preparation of smart organic semiconductors capable of dynamic structure and property modulations, promoting the studies of organic electronics from static to dynamic

Selectively Modulating Triplet Exciton Formation in Host Materials for Highly Efficient Blue Electrophosphorescence

The concept of limiting the triplet exciton formation to fundamentally alleviate triplet-involved quenching effects is introduced to construct host materials for highly efficient and stable blue phosphorescent organic light-emitting diodes (PhOLEDs). The low triplet exciton formation is realized by small triplet exciton formation fraction and rate with high binding energy and high reorganization energy of triplet exciton. Demonstrated in two analogue molecules in conventional donor–acceptor molecule structure for bipolar charge injection and transport with nearly the same frontier orbital energy levels and triplet excited energies, the new concept host material shows significantly suppressed triplet exciton formation in the host to avoid quenching effects, leading to much improved device efficiencies and stabilities. The low-voltage-driving blue PhOLED devices exhibit maximum efficiencies of 43.7 cd A^–1 for current efficiency, 32.7 lm W^–1 for power efficiency, and 20.7% for external quantum efficiency with low roll-off and remarkable relative quenching effect reduction ratio up to 41%. Our fundamental solution for preventing quenching effects of long-lived triplet excitons provides exciting opportunities for fabricating high-performance devices using the advanced host materials with intrinsically small triplet exciton formation cross section

Achieving Optimal Self-Adaptivity for Dynamic Tuning of Organic Semiconductors through Resonance Engineering

Current static-state explorations of organic semiconductors for optimal material properties and device performance are hindered by limited insights into the dynamically changed molecular states and charge transport and energy transfer processes upon device operation. Here, we propose a simple yet successful strategy, resonance variation-based dynamic adaptation (RVDA), to realize optimized self-adaptive properties in donor–resonance–acceptor molecules by engineering the resonance variation for dynamic tuning of organic semiconductors. Organic light-emitting diodes hosted by these RVDA materials exhibit remarkably high performance, with external quantum efficiencies up to 21.7% and favorable device stability. Our approach, which supports simultaneous realization of dynamically adapted and selectively enhanced properties via resonance engineering, illustrates a feasible design map for the preparation of smart organic semiconductors capable of dynamic structure and property modulations, promoting the studies of organic electronics from static to dynamic

Bromine-Terminated Additives for Phase-Separated Morphology Control of PTB7:PC₇₁BM-Based Polymer Solar Cells

Trace amounts of solvent additive can effectively regulate the phase-separated morphology of the active layer composed of donor and acceptor materials for improved power conversion efficiency (PCE) of polymer solar cells (PSCs). However, applicable solvent additives for PSCs are still limited, and it is difficult to rationally design or select appropriate solvent additives for optimal morphology control of the active layer, mainly due to the lack of sufficient understanding of the morphological regulation mechanism. Here, on the basis of a series of bromine-terminated additives with different chain lengths, we systematically investigated the relations between properties of solvent additives, active layer morphology, and photovoltaic performance of PTB7:PC₇₁BM bulk heterojunction PSCs. In addition to the widely acknowledged requirements of solvent additives with selective solubility toward one of the components in the active layer and remarkably higher boiling point than that of the host solvent, it was found that additives should also have suitable solubility parameters for the formation of nanoscale phase-separated morphology and pure PTB7 domains simultaneously. Therefore, the PTB7:PC₇₁BM-based PSCs using a small amount (3 vol %) of specific bromine-terminated additive show significant PCE enhancement up to 55% in comparison with that of additive-free devices. These results illustrate clearly the positive effects of solvent additive-induced phase-separated morphology for high photovoltaic performance, providing important understanding of morphology control and valuable clues for the rational selection and development of suitable additives for high-performance PSCs

Improving Efficiency of Blue Organic Light-Emitting Diode with Sulfobutylated Lignin Doped PEDOT as Anode Buffer Layer

Water-soluble alkyl chain sulfobutylated lignosulfonate (ASLS) doped PEDOT was prepared with lignin as raw material. Water processable PEDOT:ASLS was applied as hole injection layer (HIL) to modify ITO. Blue phosphorescent organic light-emitting diode plays a key role for full color display and are very challenging. With PEDOT:ASLS as HIL, a highly enhanced current efficiency of 37.65 cd/A was achieved. Considering our device structure, the result is even better than that of the control device using PEDOT:PSS as HIL. Compared with PSS with regular structure, strong aggregation and oxidation behavior of ASLS contribute to the hole injection capability of PEDOT:ASLS. Considering that ASLS is of disordered and amorphous structure, which is very different from poly­(styrene sulfonic acid), it is exciting that ASLS might be of promising potential as a sustainable dopant of PEDOT. More importantly, this work will guide the design of dopant of PEDOT

Enhancing Efficiency and Stability of Perovskite Solar Cells via Photosensitive Molecule-Assisted Defect Passivation

High-quality defect-free perovskite films exhibiting improved surface morphology are required for constructing highly efficient perovskite solar cells (PSCs). Incorporation of appropriate passivation molecules in perovskite films is a popular strategy to achieve this goal. Herein, the defect passivation effect of a series of photosensitive benzoyl derivatives on the perovskite layer is investigated through the comprehensive analysis of perovskite film and corresponding solar cells. Photosensitive molecules introduced with carbonyl groups considerably diminish the defects of Pb2+ and MA+ by forming either coordinate bonds or hydrogen bonds. The ultraviolet (UV) photoinitiation properties of benzoyl derivatives help sufficiently restrain the photodegradation of perovskites during device operation. In addition, photosensitive molecule-assisted passivation strategy effectively inhibits unwanted defect-assisted recombination, improving the power conversion efficiency (PCE) from 16.94% to 19.64%. Meanwhile, passivated devices exhibit considerably enhanced light stability, with >80% of the initial PCE maintained under continuous 1 sun illumination for 700 h. This approach aids in fabricating defect-free and UV-resistant perovskite-based photoactive layers for highly efficient and stable PSCs

Tunable Nonvolatile Memory Behaviors of PCBM–MoS₂ 2D Nanocomposites through Surface Deposition Ratio Control

Efficient preparation of single-layer two-dimensional (2D) transition metal dichalcogenides, especially molybdenum disulfide (MoS₂), offers readily available 2D surface in nanoscale to template various materials to form nanocomposites with van der Waals heterostructures (vdWHs), opening up a new dimension for the design of functional electronic and optoelectronic materials and devices. Here, we report the tunable memory properties of the facilely prepared [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM)–MoS₂ nanocomposites in a conventional diode device structure, where the vdWHs dominate the electric characteristics of the devices for various memory behaviors depending on different surface deposition ratios of PCBM on MoS₂ nanosheets. Both nonvolatile WORM and flash memory devices have been realized using the new developed PCBM–MoS₂ 2D composites. Specially, the flash characteristic devices show rewritable resistive switching with low switching voltages (∼2 V), high current on/off ratios (∼3 × 10²), and superior electrical bistability (>10⁴ s). This research, through successfully allocating massive vdWHs on the MoS₂ surface for organic/inorganic 2D nanocomposites, illustrates the great potential of 2D vdWHs in rectifying the electronic properties for high-performance memory devices and paves a way for the design of promising 2D nanocomposites with electronically active vdWHs for advanced device applications