Due to their wide tunable bandgaps, high absorption coefficients, easy solution processabilities, and high stabilities in air, lead sulfide (PbS) quantum dots (QDs) are increasingly regarded as promising material candidates for next-generation light, low-cost, and flexible photodetectors. Current single-layer PbS-QD photodetectors suffer from shortcomings of large dark currents, low on-off ratios, and slow light responses. Integration with metal nanoparticles, organics, and high-conducting graphene/nanotube to form hybrid PbS-QD devices are proved capable of enhancing photoresponsivity; but these approaches always bring in other problems that can severely hamper the improvement of the overall device performance. To overcome the hurdles current single-layer and hybrid PbS-QD photodetectors face, here a bilayer QD-only device is designed, which can be integrated on flexible polyimide substrate and significantly outperforms the conventional single-layer devices in response speed, detectivity, linear dynamic range, and signal-to-noise ratio, along with comparable responsivity. The results which are obtained here should be of great values in studying and designing advanced QD-based photodetectors for applications in future flexible optoelectronics.

Recently, impressive external quantum efficiencies (EQEs) exceeding 20% are obtained for green, red, and near-infrared perovskitebased LEDs (PeLEDs) through the efforts of perovskite material optimization and device architecture design. [8-10] These achievements firmly prompt the potential applications of PeLEDs in display and illumination fields. However, compared with the efficient PeLEDs, there is only moderate performance reported for blue PeLEDs, [11-18] which undoubtedly restrict PeLED applications in full-color displays and white-light illumination. Thus, the breakthroughs of the device performance are urgently required for blue PeLEDs. Substantial efforts have been made in the past several years to obtain blue perovskite emitters, such as perovskite nanocrystals (NCs), [19-25] 2D perovskite nanoplatelets, [26-32] and quasi-2D perovskites. [33-39] In particular, the quasi-2D perovskites are rising as efficient luminescent materials for highly performed blue PeLEDs due to the cascade energy landscape for efficient exciton transfer and the subsequent radiative recombination. Typically, the quasi-2D perovskites have a formula of B 2 (APbBr 3) n−1 PbBr 4 , While there has been extensive investigation into modulating quasi-2D perovskite compositions in light-emitting diodes (LEDs) for promoting their electroluminescence, very few reports have studied approaches involving enhancement of the energy transfer between quasi-2D perovskite layers of the film, which plays very important role for achieving high-performance perovskite LEDs (PeLEDs). In this work, a bifunctional ligand of 4-(2-aminoethyl)benzoic acid (ABA) cation is strategically introduced into the perovskite to diminish the weak van der Waals gap between individual perovskite layers for promoting coupled quasi-2D perovskite layers. In particular, the strengthened interaction between coupled quasi-2D perovskite layers favors an efficient energy transfer in the perovskite films. The introduced ABA can also simultaneously passivate the perovskite defects by reducing metallic Pb for less nonradiative recombination loss. Benefiting from the advanced properties of ABA incorporated perovskites, highly efficient blue PeLEDs with external quantum efficiency of 10.11% and a very long operational stability of 81.3 min, among the best performing blue quasi-2D PeLEDs, are achieved. Consequently, this work contributes an effective approach for high-performance and stable blue PeLEDs toward practical applications. Metal halide perovskites have emerged as competitive candidates for the next-generation light-emitting diodes (LEDs) due to their excellent optical properties, such as tunable light emission color, high color purity, and high photoluminescence The ORCID identification number(s) for the author(s) of this article can be found under

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Owing to their ease of fabrication, low cost, and high flexibility, organic materials have attracted great interests in photodetector (PD) applications. However, suffering from large dark current, small photocurrent, low on–off ratio, and low sensitivity, performances of bare organic‐based PDs are not satisfactory. Integrating organic materials with other novel semiconductor materials offers an opportunity to overcome these drawbacks. Here, a lateral hybrid organic/lead sulfide (PbS) quantum dot bilayer PD is designed and fabricated, which significantly suppresses the dark current and enhances the photocurrent, leading to improved light detecting capability. Meanwhile, the bilayer PD can be made on a flexible polyimide substrate.

Quasi-two-dimensional (quasi-2D) perovskite is rising as a promising luminescent material for blue perovskite light-emitting diodes (PeLEDs). However, typical quasi-2D perovskites show a wide distribution of low-order phases and low efficiency owing to the inefficient energy transfer. Meanwhile, the defects and traps generated during the perovskite crystallization increase nonradiative recombination, further aggravating the external quantum efficiency (EQE). Herein, we demonstrate a unique quasi-2D perovskite with low-order phase suppression and defect passivation for efficient energy transfer and light emission by incorporating a 2D perovskite and an excess ammonium salt into the quasi-2D perovskite solution. By optimizing the new class of quasi-2D perovskite, we achieve blue PeLEDs with the brightness of 1765 cd m–2, EQE of 7.51%, low turn-on voltage of 3.07 V, and long operation lifetime of 3961 s under constant driving current without any shift of the electroluminescence spectra. The work contributes to promoting efficient and stable blue PeLEDs.

Substantial progress has been made in blue perovskite light-emitting diodes (PeLEDs). In this review, the strategies for high-performance blue PeLEDs are described, and the main focus is on the optimization of the optical and electrical properties of perovskites. In detail, the fundamental device working principles are first elucidated, followed by a systematical discussion of the key issues for achieving high-quality perovskite nanocrystals (NCs) and quasi-2D perovskites. These involve ligand optimization and metal doping in enhancing the carrier transport and reducing the traps of perovskite NCs, as well as the perovskite phase modulation and defect passivation in improving energy transfer and emission efficiency of quasi-2D perovskites. The strategies for efficient 3D mixed-halide perovskite and lead-free perovskite blue LEDs are then briefly introduced. After that, other strategies, including effective charge transport layer, efficient perovskite emission system, and effective device architecture for high light outcoupling efficiency, are further discussed to boost the blue PeLED performances. Meanwhile, the testing standard of blue PeLED lifetime is suggested to enable the direct comparisons of the device operational stability. Finally, challenges and future directions for blue PeLEDs are addressed.

Substantial achievements have been made in green and red perovskite light emitting diodes (PeLEDs) recently. However, blue PeLEDs still lag behind with much lower performances. One of the main reasons is the mass undesirable nonradiative recombination at interfaces and within the perovskite films. In this work, an efficient hole transport bi-layer structure composed of PSSNa and NiO x is demonstrated to simultaneously inhibit the nonradiative decays between NiO x and perovskite films by reducing NiO x surface defects and improving quasi-2D perovskite thin film quality by minimizing its pin-holes and reducing the film roughness. The results show that the dipole feature of PSSNa improves the hole transportation and thus PeLED performances. Moreover, by introducing KBr into the perovskite, its film quality improves and trap states reduce. Eventually, the blue PeLEDs is achieved with a very low turn-on voltage of 3.31 V accompanied with an external quantum efficiency of 1.45% and a remarkable luminance of 4359 cd m -2 . With further optimization of the perovskite precursor concentration, the highest luminance reaches 5737 cd m -2 , which represents the brightest blue PeLEDs reported to date as far as it is known. Furthermore, the devices also show better spectral stability and operation lifetime as compared to other blue PeLEDs.

Benefiting from the suppressed charge recombination occurring at the photoanode/electrolyte interfaces with the introduction of TEOS additive in the polysulfide electrolyte, a remarkable PCE of over 12% was obtained for ZCISe QDSCs.