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Herein, a novel molecular SO2‐Bri‐DSB based on the sulfone‐bridged distyrylbenzene derivative is synthesized, and its organic crystal is fabricated. It has a very high photoluminescence (PL) quantum efficiency in the solution and crystalline state, i.e., dual‐state emission (DSE), and the corresponding PL mechanism is clarified in detail using the transient absorption and transient PL test. The PL behaviors in the monomolecular state and organic crystal are compared. In addition, the optical anisotropy of the SO2‐Bri‐DSB crystal is thoroughly investigated using various polarization‐dependent spectroscopy techniques. The time evolution of anisotropy is composed of a step behavior caused by the anisotropy of the electronic transition and a slow enhancing process with a lifetime of 4.86 ns, which is governed by the change in emission lifetime due to the anisotropy. The space‐resolved evolution of the optical anisotropy is investigated using the polarization‐dependent light wave‐guiding test and exhibits that the emission anisotropy gradually decreases with length, and it has a longer effective propagation length than the polarization emission signal. The findings provide insight into the intrinsic optical anisotropy of single‐molecular crystals and indicate that these materials have enormous potential in the domains of polarization lighting and display. [ABSTRACT FROM AUTHOR]

Currently, the performance of quantum‐dot light‐emitting diodes (QLEDs) based on environmental‐friendly Cu─In─Zn─S quantum dots (QDs) still lags far behind that of Cd‐QDs‐based devices. Here it is demonstrated that the unique trap‐related recombination in Cu─In─Zn─S QDs is mainly responsible for the low device efficiency. The luminous efficiency of Cu─In─Zn─S‐based QLEDs is rather sensitive to the temperature and hole‐transporting layers (HTLs) due to the susceptible thermal‐related trappingdetrapping processes of holes in radiative Cu‐related traps. The holes in Cu‐related traps can be quenched by escaping to the valence band of the QDs or/and transferring to the adjacent HTLs. An HTL with low highest occupied molecular orbitals is desired to enhance the hole injection and hinder the aforementioned hole transfer. As a result, a high device efficiency of 6.0 cd A−1 is achieved at room temperature, which is attributed to suppressed HTL‐induced emission quenching and efficient valence‐band‐dominated hole injection from HTL to the QDs. The device efficiency is further increased to 13.2 cd A−1 at 150K by suppressing thermal‐induced quenching. [ABSTRACT FROM AUTHOR]

A clear understanding on the fundamental working mechanisms of quantum‐dot light emitting diodes (QLEDs), especially the blue devices, is always sought after. Here the electroluminescence (EL) turn‐on mechanism of blue QLEDs is unraveled by structure engineering of the hole‐transport layers (HTLs). It is demonstrated that the EL turn‐on in blue QLEDs is highly dependent on the charge‐transport polarity of the HTLs. Energy transfer between HTLs and the blue quantum dots (QDs) occurs for the QLEDs based on bipolar HTLs, and, in contrast, charge injection is responsible for EL turn‐on of the blue devices consisting of unipolar HTLs. In addition, large hole‐injection barrier results in serious accumulation of holes at the interface of HTLs/QDs, then inducing serious electrons leakage into the HTLs, thereby leading to poor device efficiency under low driving current. It is suggested here that confining the carriers to the quantum dots and reducing the hole‐injection barrier remain two critical aspects to optimize the performance of blue QLEDs. [ABSTRACT FROM AUTHOR]

The emergence of planar electroluminescent diodes (including polymer light‐emitting diodes, organic light‐emitting diodes, quantum‐dot light‐emitting diodes, and perovskite light‐emitting diodes) is causing a revolution in displays, lighting, and wearable electronic devices. Continuous advancement in the comprehension and management of charge carrier dynamics in these devices has led to several significant breakthroughs, including diodes with ultrahigh luminance, memory devices, and amplified spontaneous emission. Transient electroluminescence (TrEL) spectroscopy is a relative powerful technology to investigate charge dynamics, including transport, distribution, and storage of charge carriers, in electrically‐driven planar light‐emitting diodes (LEDs). The aim of this review is to revisit the principle and applications of TrEL spectroscopy in planar electroluminescent diodes, and to evaluate the reliability of various parameters extracted using this technology. A particular focus is on electroluminescence response time, charge‐carrier transport and storage, and exciton species. First, the principle and equipment system of the TrEL, as well as specific attention during TrEL measurements are described in detail, following by the applications TrEL spectroscopy in planar LEDs. Further development on the TrEL technology is discussed in the third section. Finally, a summary and outlook for the TrEL are shown and challenges faced by the TrEL spectroscopy are also highlighted. [ABSTRACT FROM AUTHOR]

Low-dimensional networked organic-inorganic hybrid metal halide crystal has become an emerging hotspot material due to its opportunities and advantages in the development of white-light-emitting diodes. Therefore, its photoluminescence (PL) mechanism is important. Herein, we study the PL behavior of columniform TPP 2 MnBr 4 crystals using multi-spectroscopy. The temperature-dependent PL data show that the PL of the TPP 2 MnBr 4 crystal originates from the recombination of a self-trapping exciton. A polarization-dependent PL test suggests that the self-trapping exciton is anisotropic, which indicates that the distribution of self-trapping states is sensitive to the orientation of the crystal axis. Space-resolved PL spectroscopy shows that the anisotropy of PL gradually weakens along the orientation of the columniform crystal, which has a longer relaxation distance than traditional light-wave-guiding behavior. Thus, anisotropy of PL can exist before it disappears in the crystal. Our results elucidate the PL mechanism of low-dimensional networked organic-inorganic hybrid metal halide crystals and provide a foundation for advanced optical polarization devices based on them.

Quasi-2D halide perovskites have potential in lasing due to their amplified spontaneous emission (ASE) properties. The ASE of (PBA) 2 MA n -1 Pb n Br 3 n +1 thin films has been confirmed by photoluminescence (PL) testing using stripe light excitation (SLE). The ASE threshold decreases with decreasing environmental temperature ( T E ) or increasing number of inorganic layers ( n ). Using the transient absorption technique, the Auger recombination and the cooling process of the high-activity carrier are accelerated with the decrease of n or T E . A new ASE mechanism is proposed where high-activity carriers directly emit photons under photon perturbation from adjacent sites, leading to the accumulation and amplification of emitted photons only in the SLE region for ASE to occur. In addition, the reduction of n promotes light scattering between nano-thin layers, which supports a rapid increase in the ASE signal after the ASE threshold is crossed.