Current efforts to reduce the density of structural defects such as surface passivation, doping, and modified synthetic protocols have allowed us to grow high-quality perovskite nanocrystals (PNCs). However, the role of the purity of the precursors involved during the PNC synthesis to hinder the emergence of defects has not been widely explored. In this work, we analyzed the use of different crystallization processes of PbX2 (X = Cl– or I–) to purify the chemicals and produce highly luminescent and stable CsPbCl3–x Br x and CsPbI3 PNCs. The use of a hydrothermal (Hyd) process to improve the quality of the as-prepared PbCl2 provides blue-emitting PNCs with efficient ligand surface passivation, a maximum photoluminescence quantum yield (PLQY) of ∼ 88%, and improved photocatalytic activity to oxidize benzyl alcohol, yielding 40%. Then, the hot recrystallization of PbI2 prior to Hyd treatment led to the formation of red-emissive PNCs with a PLQY of up to 100%, long-term stability around 4 months under ambient air, and a relative humidity of 50–60%. Thus, CsPbI3 light-emitting diodes were fabricated to provide a maximum external quantum efficiency of up to 13.6%. We claim that the improvement of the PbX2 crystallinity offers a suitable stoichiometry in the PNC structure, reducing nonradiative carrier traps and so maximizing the radiative recombination dynamics. This contribution gives an insight into how the manipulation of the PbX2 precursor is a profitable and potential alternative to synthesize PNCs with improved photophysical features by making use of defect engineering.

and discharge of the carriers at the contact layers; [12,[25][26][27] however, these phenomena are currently not very well understood.The light emission kinetics in perovskite LEDs and in organic light-emitting diodes (OLEDs) is usually investigated using a range of steady-state and timeresolved methods. [26,28] Remarkably, frequency-resolved methods such as impedance spectroscopy (IS) are highly effective for the separation of concomitant kinetic phenomena. [29] The connection between time transients and light-stimulated frequency methods in halide perovskite has been reviewed recently. [30] Here, we explore a new experimental measuring technique that can provide significant information about recombination in high-performance solar cells and LEDs. We analyze the frequency-resolved light emission with respect to an applied modu lated voltage, that we denote light emission voltage modulated spectroscopy (LEVS). The main point of this investigation is to reveal significant features of the radiative charge recombination that are difficult to be discerned in other measurement techniques. [30] This methodology will be especially useful when the radiative recombination event is convoluted with previous electronic carrier steps such as transport, trapping, or contact polarization effects, and/or ionic-related phenomena. It has previously been remarked that the capacitance and luminance of LEDs show correlated features [21,31,32] and some studies of electrically stimulated light emission spectroscopy have been reported, [33][34][35] but unfortunately, a general methodology has not been fully developed.Here we describe the first LEVS experiments in halide perovskite LEDs and establish an equivalent circuit model to understand the observed spectra, based on the previous experience in IS. We show that the method provides unique information on the recombination processes that cannot be accessed by purely electrical techniques, thus highlighting the interest of this new experimental technique for the characterization of optoelectronic devices, especially those presenting multiple physical phenomena, as it is the case of halide perovskite-based systems. The Transfer Functions of Frequency Resolved Measurements IS is a general-purpose characterization technique that is used in a large variety of fields to extract dynamic information on anyThe kinetics of light emission in halide perovskite light-emitting diodes (LEDs) and solar cells is composed of a radiative recombination of voltage-injected carriers mediated by additional steps such as carrier trapping, redistribution of injected carriers, and photon recycling that affect the observed luminescence decays. These processes are investigated in high-performance halide perovskite LEDs, with external quantum efficiency (EQE) and luminance values higher than 20% and 80 000 Cd m −2 , by measuring the frequency-resolved emitted light with respect to modulated voltage through a new methodology termed light emission voltage modulated spectroscopy (LEVS). The spectra are shown to provid...

The use of non-toxic and low-cost vitamins like α-tocopherol (α-TCP, vitamin E) to improve the photophysical properties and stability of perovskite nanocrystals (PNCs), through post-synthetic ligand surface passivation, is demonstrated for the first time. Especially interesting is its effect on CsPbI 3 the most unstable inorganic PNC. Adding α-TCP produces that the photoluminescence quantum yield (PLQY) of freshly prepared and aged PNCs achieves values of ≈98% and 100%, respectively. After storing 2 months under ambient air and 60% relative humidity, PLQY is maintained at 85% and 67%, respectively. α-TCP restores the PL features of aged CsPbI 3 PNCs, and mediates the radiative recombination channels by reducing surface defects. In addition, the combination of α-TCP and PNCs facilitates the chemical formulation to prepare PNCs-acrylic polymer composites processable by additive manufacturing. This enables the development of complex shaped parts with improved luminescent features and long-term stability for 4 months, which is not possible for non-modified PNCs. A PLQY ≈92% is reached in the 3D printed polymer/PNC composite, the highest value obtained for a red-emitting composite solid until now as far as it is known. The passivation shell provided by α-TCP makes that PNCs inks do not suffer any degradation process avoiding the contact with the environment and preserve their properties after reacting with polar monomers during composite polymerization.

Halide perovskite nanocrystals (PNCs) exhibit growing attention in optoelectronics due to their fascinating color purity and improved intrinsic properties. However, structural defects emerging in PNCs progressively hinder the radiative recombination and carrier transfer dynamics, limiting the performance of light-emitting devices. In this work, we explored the introduction of guanidinium (GA + ) during the synthesis of high-quality Cs 1−x GA x PbI 3 PNCs as a promising approach for the fabrication of efficient bright-red light-emitting diodes (R-LEDs). The substitution of Cs by 10 mol % GA allows the preparation of mixed-cation PNCs with PLQY up to 100% and long-term stability for 180 days, stored under air atmosphere and refrigerated condition (4 °C). Here, GA + cations fill/replace Cs + positions into the PNCs, compensating intrinsic defect sites and suppressing the nonradiative recombination pathway. LEDs fabricated with this optimum material show an external quantum efficiency (EQE) near to 19%, at an operational voltage of 5 V (50−100 cd/m 2 ) and an operational half-time (t 50 ) increased 67% respect CsPbI 3 R-LEDs. Our findings show the possibility to compensate the deficiency through A-site cation addition during the material synthesis, obtaining less defective PNCs for efficient and stable optoelectronic devices.

After establishing themselves as promising active materials in the field of solar cells, halide perovskites are currently being explored for fabrication of low‐cost, easily processable and highly efficient light emitting diodes (LEDs). Despite this, the highest efficiencies reported for perovskite‐based LEDs (PeLEDs) have been achieved through spin‐coating or vacuum evaporation deposition techniques, which are not adequate, in most of the cases, for an industrial scale production. Additionally, the long‐term stability is still a big handicap, even though all inorganic perovskites, such as CsPbBr3, are found to be more stable to external variables. In this context, herein we report on the fabrication of fully inkjet‐printed (IJP) CsPbBr3‐based PeLEDs in ambient conditions, on rigid and flexible substrates, on a proof‐of‐concept basis, with the successful incorporation of NiO and SnO2 as hole and electron selective contacts, respectively. Despite the moderate luminance (324 cd/m2) value obtained, this result pave the way towards the development of up‐scalable fabrication of PeLEDs based on deposition techniques with controlled spatial resolution.This article is protected by copyright. All rights reserved.