Enhanced Thermally Activated Delayed Fluorescence by Sole Coordination: From an Organic Molecule to Its Zinc Complex.

A BPAPTPyC organic molecule containing a sandwich structural chromophore is designed and synthesized to produce blue thermally activated delayed fluorescence (TADF). The chromophore is composed of two di(4--butylphenyl)amino donors and one inserted terpyridyl acceptor hitched at positions 1, 8, and 9 of a single carbazole via the -phenylene group, in which the multiple space π-π interactions between the donor and acceptor enable the molecule to possess the TADF feature with a high energy emission at 470 nm but a low photoluminescence quantum yield (PLQY) and a small proportion of the delayed component. In contrast, the corresponding Zn(BPAPTPyC)Cl complex has a high PLQY and a short lifetime with a red-shifted emission due to the enhanced rigidity and electron accepting ability of the terpyridyl group from coordination.

Improved Hole-Selective Contact Enables Highly Efficient and Stable FAPbBr Perovskite Solar Cells and Semitransparent Modules.

Self-assembled monolayers (SAMs) as the hole-selective contact have achieved remarkable success in iodine-based perovskite solar cells (PSCs), while their impact on bromine-based PSCs is limited due to the poor perovskite crystallization behavior and mismatched energy level alignment. Here, a highly efficient SAM of (2-(3,6-diiodo-9H-carbazol-9-yl)ethyl)phosphonic acid (I-2PACz) is employed to address these challenges in FAPbBr-based PSCs. The incorporation of I atoms into I-2PACz not only releases tensile stress within FAPbBr perovskite, promoting oriented crystallization and minimizing defects through halogen-halogen bond, but also optimizes the energy levels alignment at hole-selective interface for enhanced hole extraction.

Enhancing Stability and Performance in Tin-Based Perovskite Field-Effect Transistors Through Hydrogen Bond Suppression of Organic Cation Migration.

Ion migration poses a substantial challenge in perovskite transistors, exerting detrimental effects on hysteresis and operational stability. This study focuses on elucidating the influence of ion migration on the performance of tin-based perovskite field-effect transistors (FETs). It is revealed that the high background carrier density in FASnI FETs arises not only from the oxidation of Sn but also from the migration of FA ions.

Multi-Functional Spirobifluorene Phosphonate Based Exciplex Interface Enables V Reaching 95% of Theoretical Limit for Perovskite Solar Cells.

Metal halide perovskite solar cells (PSCs) show significant advancements in power conversion efficiency (PCE). However, the open-circuit voltage (V) of PSCs is limited by interfacial factors such as defect-induced recombination, energy band mismatch, and non-intimate interface contact. Here, an exciplex interface is first developed based on the strategically designed and synthesized two spirobifluorene phosphonate molecules to mitigate V loss in PSCs.

Phosphate ester functionalized fluorene-benzothiadiazole alternating copolymer/hydroxylated g-CN heterojunctions for efficient hydrogen evolution under visible-light irradiation.

It is highly desirable to explore functionalized polymer semiconductor/g-CN heterojunction photocatalysts with the tight interfacial connection for promoting the photogenerated electron-hole pair separation, improving the hydrophilicity, extending the visible light response and achieving the efficient visible light-driven H evolution. Herein, we synthesized novel poly[9,9-bis(3-ethyl phosphate propyl)fluorene-alt-benzothiadiazole] (PPFBT) with a phosphate ester on every repeating unit by the Suzuki polymerization and then fabricated PPFBT/hydroxylated g-CN (PPFBT/CN-OH) heterojunctions via a surface hydroxyl-induced assembly process. The ratio-optimized 5PPFBT/CN-OH shows the hydrogen evolution activity of 2662.

Room-Temperature Continuous-Wave Microcavity Lasers from Solution-Processed Smooth Quasi-2D Perovskite Films with Low Thresholds.

Continuous-wave (CW) lasing in quasi-two-dimensional (2D) perovskite-based distributed feedback cavities has been achieved at room temperature; however, CW microcavity lasers comprising distributed Bragg reflectors (DBRs) have rarely been prepared using solution-processed quasi-2D perovskite films because the roughness of perovskite films significantly increases intersurface scattering loss in the microcavity. Herein, high-quality spin-coated quasi-2D perovskite gain films were prepared using an antisolvent to reduce roughness. The highly reflective top DBR mirrors were deposited via room-temperature e-beam evaporation to protect the perovskite gain layer.

Enhanced Circularly Polarized Photoluminescence of Chiral Perovskite Films by Surface Passivation with Chiral Amines.

Hybrid organic-inorganic perovskites have shown promise in circularly polarized light source applications when chirality has been introduced. Circularly polarized photoluminescence (CPL) is a significant tool for investigating the chiroptical properties of perovskites. However, further research is still urgently needed, especially with regard to optimization.

Insight into Diphenyl Phosphine Oxygen-Based Molecular Additives as Defect Passivators toward Efficient Quasi-2D Perovskite Light-Emitting Diodes.

The introduction of additives has become an important method for enhancing the device performance of quasi-two-dimensional perovskite light-emitting diodes. In this work, we systematically studied the electronic and spatial effects of molecular additives on defect passivation abilities using the methyl, hydrogen, and hydroxyl groups substituted three diphenyl phosphine oxygen additives. The electron-donating conjugation effect of the hydroxyl group on diphenylphosphinic acid (OH-DPPO) leads to a more electron-rich region in OH-DPPO, and the hydroxyl group has a moderate steric hindrance.

A cyano-based electron-accepting building block to design n-type conjugated polymers with absorption wavelength of >1000 nm.

There are much fewer n-type conjugated polymers than p-type counterparts because of the lack of strong electron-accepting building blocks. We report a novel strong electron-accepting unit based on a dicyanomethylene unit. The resulting polymers exhibit LUMO energy levels of as low as -4.

Suppressing High-Order Phase for Efficient Pure Red Quasi-2D Perovskite Light-Emitting Diodes.

Quasi-two-dimensional (quasi-2D) perovskites are promising for the realization of spectrally stable pure red perovskite light-emitting diodes (PeLEDs) with a single iodide component, because they avoid the halide separation that red three-dimensional perovskites of mixed halides have faced. However, the distribution of high-order phases in solution-processed quasi-2D perovskite films causes the spectral shift away from the pure red region. Here, we introduced a simple approach of adding excessive ligand combinations to redistribute the phase distribution of quasi-2D perovskite and to inhibit the high-order phase.

Comprehensive Passivation for High-Performance Quasi-2D Perovskite LEDs.

Quasi-2D perovskites have demonstrated great application potential in light-emitting diodes (LEDs). Defect passivation with chemicals plays a critical role to achieve high efficiency. However, there are still challenges in comprehensively passivating the defects distributed at surface, bulk, and buried interface of quasi-2D perovskite emitting films, hindering the further improvement of device performance.

Suppressing thermal quenching via defect passivation for efficient quasi-2D perovskite light-emitting diodes.

Emission thermal quenching is commonly observed in quasi-2D perovskite emitters, which causes the severe drop in luminescence efficiency for the quasi-2D perovskite light-emitting diodes (PeLEDs) during practical operations. However, this issue is often neglected and rarely studied, and the root cause of the thermal quenching has not been completely revealed now. Here, we develop a passivation strategy via the 2,7-dibromo-9,9-bis (3'-diethoxylphosphorylpropyl)-fluorene to investigate and suppress the thermal quenching.

Phosphonate/Phosphine Oxide Dyad Additive for Efficient Perovskite Light-Emitting Diodes.

Additives play a critical role for efficient perovskite light-emitting diodes (PeLEDs). Here, we report a novel phosphonate/phosphine oxide dyad molecular additive (PE-TPPO), with unique dual roles of passivating defects and enhancing carrier radiative recombination, to boost the device efficiency of metal-halide perovskites. In addition to the defect passivation effect of the phosphine oxide group to enhance the photoluminescence intensity and homogeneity of perovskite film, the phosphonate group with strong electron affinity can capture the injected electrons to increase local carrier concentration and accelerate the carrier radiative recombination in the electroluminescence process.

Engineering of Annealing and Surface Passivation toward Efficient and Stable Quasi-2D Perovskite Light-Emitting Diodes.

Solution-processed quasi-two-dimensional (quasi-2D) perovskites with self-assembled multiple quantum well (QW) structures exhibit enhanced exciton binding energy, which is ideal for use as light emitters. Here, we have found that postannealing is important to promoting the QWs' composition transfer, and we explored the correlation among the annealing time, the external quantum efficiency (EQE), and the operational stability of the device. During thermal annealing, the low- QWs will gradually convert to high- phases, accompanied by an increase in grain size.

Stable room-temperature continuous-wave lasing in quasi-2D perovskite films.

Organic-inorganic lead halide quasi-two-dimensional (2D) perovskites are promising gain media for lasing applications because of their low cost, tunable colour, excellent stability and solution processability. Optically pumped continuous-wave (CW) lasing is highly desired for practical applications in high-density integrated optoelectronics devices and constitutes a key step towards electrically pumped lasers. However, CW lasing has not yet been realized at room temperature because of the 'lasing death' phenomenon (the abrupt termination of lasing under CW optical pumping), the cause of which remains unknown.

Detrimental Effect of Unreacted PbI on the Long-Term Stability of Perovskite Solar Cells.

Excess/unreacted lead iodide (PbI ) has been commonly used in perovskite films for the state-of-the-art solar cell applications. However, an understanding of intrinsic degradation mechanisms of perovskite solar cells (PSCs) containing unreacted PbI has been still insufficient and, therefore, needs to be clarified for better operational durability. Here, it is shown that degradation of PSCs is hastened by unreacted PbI crystals under continuous light illumination.

Detecting and identifying reversible changes in perovskite solar cells by electrochemical impedance spectroscopy.

The current status of electrochemical impedance spectroscopy (EIS) and related analysis on perovskite solar cells (PSC) is still unsatisfactory. The provided models are still vague and not really helpful for guiding the efforts to develop more efficient and stable devices. Due to the slow and complex dynamics of these devices, the obtained spectra need to be validated, which is hardly ever done.

High performance from extraordinarily thick organic light-emitting diodes.

Organic light-emitting diode (OLED) technology is promising for applications in next-generation displays and lighting. However, it is difficult-especially in large-area mass production-to cover a large substrate uniformly with organic layers, and variations in thickness cause the formation of shunting paths between electrodes, thereby lowering device production yield. To overcome this issue, thicker organic transport layers are desirable because they can cover particles and residue on substrates, but increasing their thickness increases the driving voltage because of the intrinsically low charge-carrier mobilities of organics.

The Relation of Phase-Transition Effects and Thermal Stability of Planar Perovskite Solar Cells.

A power conversion efficiency of over 20% has been achieved in CHNHPbI-based perovskite solar cells (PSC), however, low thermal stability associated with the presence of a phase transition between tetragonal and cubic structures near room temperature is a major issue that must be overcome for future practical applications. Here, the influence of the phase transition on the thermal stability of PSCs is investigated in detail by comparing four kinds of perovskite films with different compositions of halogen atoms and organic components. Thermally stimulated current measurements reveal that a large number of carrier traps are generated in solar cells with the perovskite CHNHPbI as a light absorber after operation at 85 °C, which is higher than the phase-transition temperature.

Enhanced Electroluminescence from Organic Light-Emitting Diodes with an Organic-Inorganic Perovskite Host Layer.

The development of host materials with high performance is essential for fabrication of efficient and stable organic light-emitting diodes (OLEDs). Although host materials used in OLEDs are typically organics, in this study, it is shown that the organic-inorganic perovskite CH NH PbCl (MAPbCl ) can be used as a host layer for OLEDs. Vacuum-evaporated MAPbCl films have a wide band gap of about 3 eV and very high and relatively balanced hole and electron mobilities, which are suitable for the host material.

Diffusion Enhancement in Highly Excited MAPbI Perovskite Layers with Additives.

Carrier mobility is one of the crucial parameters determining the electronic device performance. We apply the light-induced transient grating technique to measure independently the carrier diffusion coefficient and lifetime, and to reveal the impact of additives on carrier transport properties in wet-cast CHNHPbI (MAPbI) perovskite films. We use the high excitation regime, where diffusion length of carriers is controlled purely by carrier diffusion and not by the lifetime.

Amplified spontaneous emission in phenylethylammonium methylammonium lead iodide quasi-2D perovskites.

Organo-metal-halide perovskites are a promising set of materials for optoelectronic applications such as solar cells, light emitting diodes and lasers. Perovskite thin films have demonstrated amplified spontaneous emission thresholds as low as 1.6 μJ cm-2 and lasing thresholds as low as 0.

Deep-Red Amplified Spontaneous Emission from cis-Configured Squaraine.

We report deep-red amplified spontaneous emission (ASE) from cis-configured squaraine (cis-DCSQ1) under optical pumping. Doping of cis-DCSQ1 into a 4,4'-bis(9-carbazolyl)-2,2'-biphenyl (CBP) host film at an appropriate concentration (0.5 wt % for this system) led to a marked increase of photoluminescence quantum yield because of efficient CBP-to-cis-DCSQ1 Förster resonance energy transfer and suppression of aggregation-caused quenching.