Lead-free, stable, high-efficiency (52%) blue luminescent FA3Bi2Br9 perovskite quantum dots.

Lead halide perovskites are promising candidates as next-generation emitting materials for lighting and displays due to their superior properties. However, the toxicity of lead content severely limits their practical applications. Although lead-free Sn-based and Bi-based perovskites (Cs3Bi2Br9, MA3Bi2Br9) are reported, they all suffer from low photoluminescence quantum yield (PLQY). Here, we report the synthesis of lead-free FA3Bi2Br9 perovskite quantum dots (QDs) and their optical characterization. Through a facile ligand-assisted solution process, the as-synthesized FA3Bi2Br9 QDs exhibit a bright blue emission at 437 nm with a high PLQY of 52%. As to the origins, the observed high exciton binding energy (274.6 meV), direct bandgap nature and low defect density are proposed to guarantee the exciton generation and efficient radiative recombination. Besides, the FA3Bi2Br9 QDs show a good air stability and ethanol stability. A lead-free perovskite blue light-emitting diodes (LED) was successfully fabricated by combining FA3Bi2Br9 QDs/PS composites with a UV light chip. Our results highlight the potential of lead-free perovskites for applications in light-emitting devices.

Photon-Induced Reshaping in Perovskite Material Yields of Nanocrystals with Accurate Control of Size and Morphology.

Benefiting from morphology-/size-tunable optical features, nanocrystals have been considered promising candidates for display or lighting applications. To achieve selective characteristic emission, precise control in size and morphology is thus a prerequisite. Herein, we report that the nanosecond-pulsed laser irradiation induces CsPbBr3 reshaping, yielding precise control of size and morphology. Under 532 and 355 nm laser irradiation, polydisperse CsPbBr3 nanocrystals or raw micron powders can be reshaped into uniform sizes of 12 and 6 nm, respectively. Moreover, by tuning ligand composition, the morphology of reshaped nanocrystals can be manipulated, such as nanocubes, nanorods, or nanosheets. Results reveal that the reshaping process relies on striving for a delicate balance between energy deposition and heat dissipation under irradiation. A low dissipation rate leads to temperature rising and lattice breaking, which turn out to be the driving forces for reshaping. This feasible method provides a reliable, and scalable route toward preparation of perovskite functional nanocrystals.

Highly Efficient Visible-Light-Driven Graphene-CdS Nanocomposite Photocatalysts.

Graphene-CdS nanocomposites with different CdS contents were synthesized via a solvothermal route. Compared with pure CdS, graphene-CdS composites exhibited higher efficiency in photodegradation of methylene blue (MB) under visible light irradiation. TEM observations demonstrated that a homogeneous distribution of CdS nanoparticles on the graphene nanosheets was formed, while the CdS nanoparticles on graphene-CdS composite (1 g/7.5 mmol) distributed best among graphene-CdS composites. The results show that the graphene-CdS composite (1 g/7.5 mmol) has the highest efficiency and well stability. It demonstrated the mechanism of photodegration was that ˙OH radical generated by graphene-CdS composite plays a vital role by adding dimethyl sulfoxide (DMSO).

Two-dimensional CsPbBr3/PCBM heterojunctions for sensitive, fast and flexible photodetectors boosted by charge transfer.

Inorganic halide perovskites exhibited promising potentials for high-performance wide-band photodetectors (PDs) due to their high light absorption coefficients, long carrier diffusion length and wide light absorption ranges. Here, we report two-dimensional (2D) CsPbBr3/PCBM heterojunctions for sensitive, fast and flexible PDs, whose performances can be greatly boosted by the charge transfer through the energy-aligned interface. The 2D CsPbBr3 nanosheets with high crystallinity were fabricated via a simple solution-process at room temperature, and then assembled into flexible heterojunctions films with polymerphenyl-C61-butyric acid methyl ester (PCBM). Significantly, the efficient and fast charge transfer at the heterojunctions interface was evidenced by the obvious photoluminescence quenching and variation of recombination dynamics. Subsequently, such heterojunctions PD exhibited an enhanced responsivity of 10.85 A W-1 and an ultrahigh detectivity of 3.06 × 1013 Jones. In addition, the PD shows a broad linear dynamic range of 73 dB, a fast response speed with rise time of 44 µs and decay time of 390 µs, respectively. Moreover, the PD lying on polyethylene terephthalate substrates exhibited an outstanding mechanical flexibility and a robust electrical stability. These results could provide a new avenue for integration of 2D perovskites and organic functional materials and for high-performance flexible PDs.

Dimensionality and Interface Engineering of 2D Homologous Perovskites for Boosted Charge-Carrier Transport and Photodetection Performances.

Two-dimensional (2D) homologous halide perovskite (HP) microcrystallines have emerged as a promising alternative light-sensitive material; however, the undesirable quantum confinement effect and severe interfacial charge-carrier scattering still hamper their applications in photodetectors (PDs). Here we propose a novel postsynthetic treatment to simultaneously solve both problems. 2D (OA)2FAn-1PbnBr3n+1 (OA and FA represent octadecylamine and formamidine) microplatelet film was immersed in solution containing FA+, leading to improvements in two aspects. First, the dimensionality of 2D HPs was increased through an exchange reaction between OA+ and FA+, which meliorates the quantum confinement effect and facilitates the separation of electrons and holes; second, the free-standing 2D HP microcrystallines were fused for promoted interdomain charge-carrier transport. The treated PDs achieved a 3600 and 4200% increase in external quantum yield and responsivity up to 7100% and 32 A/W, respectively, and the rise/decay time was shortened by two orders of magnitude to 0.25/1.45 ms.

Constructing Fast Carrier Tracks into Flexible Perovskite Photodetectors To Greatly Improve Responsivity.

Intrinsically high mobility and large absorption coefficient endow inorganic halide perovskites (IHPs) with great promise for high-performance photodetectors (PDs), which, however, are being hindered by the low carrier extraction and transport efficiency of the solution assembled films. Here, we report on a general strategy to enhance the perovskite film conductivity that carbon nanotubes (CNTs) conductive nanonets are constructed from to provide fast carrier tracks. Resultantly, the CsPbBr3 nanosheet/CNT composite films exhibit both high light harvesting and high conductivity, such advantages are demonstrated by the high performances of corresponding planar PDs. Specifically, the highest external quantum efficiency (EQE) of 7488% and the highest responsivity of 31.1 A W-1 under a bias of 10 V among IHP PDs with planar structure are achieved, which are almost 125-fold over the previous best results. Besides, the efficient charge extraction and transport also remarkably contribute to the fast response speed where a rise time of 16 µs is achieved, which is also superior to state-of-the-art IHP PDs. Furthermore, the composite films exhibit impressive flexibility due to the ultrathin 2D and 1D structural characteristic of perovskites and CNTs. By deploying the PD as a point-like detector, we acquire clear images. The results indicate the promising potentials of the perovskite/CNT composites for solution and ambient condition processed flexible devices, and this strategy is general for all kinds of perovskite optoelectronic devices including photodetectors, phototransistors, and even LEDs.

All Inorganic Halide Perovskites Nanosystem: Synthesis, Structural Features, Optical Properties and Optoelectronic Applications.

The recent success of organometallic halide perovskites (OHPs) in photovoltaic devices has triggered lots of corresponding research and many perovskite analogues have been developed to look for devices with comparable performance but better stability. Upon the preparation of all inorganic halide perovskite nanocrystals (IHP NCs), research activities have soared due to their better stability, ultrahigh photoluminescence quantum yield (PL QY), and composition dependent luminescence covering the whole visible region with narrow line-width. They are expected to be promising materials for next generation lighting and display, and many other applications. Within two years, a lot of interesting results have been observed. Here, the synthesis of IHPs is reviewed, and their progresses in optoelectronic devices and optical applications, such as light-emitting diodes (LEDs), photodetectors (PDs), solar cells (SCs), and lasing, is presented. Information and recent understanding of their crystal structures and morphology modulations are addressed. Finally, a brief outlook is given, highlighting the presently main problems and their possible solutions and future development directions.