Ruddlesden–Popper phase (RP‐phase) perovskites that consist of 2D perovskite slabs interleaved with bulky organic ammonium (OA) are favorable for light‐emitting diodes (LEDs). The critical limitation of LED applications is that the insulating OA arranged in a preferred orientation limits charge transport. Therefore, the ideal solution is to achieve a randomly connected structure that can improve charge transport without hampering the confinement of the electron–hole pair. Here, a structurally modulated RP‐phase metal halide perovskite (MHP), (PEA)2(CH3NH3)m−1PbmBr3m+1 is introduced to make the randomly oriented RP‐phase unit and ensure good connection between them by applying modified nanocrystal pinning, which leads to an increase in the efficiency of perovskite LEDs (PeLEDs). The randomly connected RP‐phase MHP forces contact between inorganic layers and thereby yields efficient charge transport and radiative recombination. Combined with an optimal dimensionality, (PEA)2(CH3NH3)2Pb3Br10, the structurally modulated RP‐phase MHP exhibits increased photoluminescence quantum efficiency, from 0.35% to 30.3%, and their PeLEDs show a 2,018 times higher current efficiency (20.18 cd A−1) than in the 2D PeLED (0.01 cd A−1) and 673 times than in the 3D PeLED (0.03 cd A−1) using the same film formation process. This approach provides insight on how to solve the limitation of RP‐phase MHP for efficient PeLEDs.

We have achieved high-efficiency polycrystalline perovskite light-emitting diodes (PeLEDs) based on formamidinium (FA) and cesium (Cs) mixed cations without quantum dot synthesis. Uniform single-phase FACs PbBr polycrystalline films were fabricated by one-step formation with various FA:Cs molar proportions; then the influences of chemical composition on film morphology, crystal structure, photoluminescence (PL), and electroluminescence (EL) were systematically investigated. Incorporation of Cs cations in FAPbBr significantly reduced the average grain size (to 199 nm for FA:Cs = 90:10) and trap density; these changes consequently increased PL quantum efficiency (PLQE) and PL lifetime of FACs PbBr films and current efficiency (CE) of PeLEDs. Further increase in Cs molar proportion from 10 mol % decreased crystallinity and purity, increased trap density, and correspondingly decreased PLQE, PL lifetime, and CE. Incorporation of Cs also increased photostability of FACs PbBr films, possibly due to suppressed formation of light-induced metastable states. FACs PbBr PeLEDs show the maximum CE = 14.5 cd A at FA:Cs = 90:10 with very narrow EL spectral width (21-24 nm); this is the highest CE among FA-Cs-based PeLEDs reported to date. This work provides an understanding of the influences of Cs incorporation on the chemical, structural, and luminescent properties of FAPbBr polycrystalline films and a breakthrough to increase the efficiency of FACs PbBr PeLEDs.

Experimental methods, fluence dependent pump-probe signal, fluence dependence kinetics, fitting of high energy tail of pump-probe spectra (link).

This work reports a straightforward and scalable low-temperature synthesis of methylammonium lead tri-iodide (MAPbI 3 ) perovskite particles. Inks are formulated in benign solvents and are printed in ambient conditions for the fabrication of a light detector with high detectivity. SUMMARYHere, we propose a simple and low-temperature approach for the synthesis of methylammonium lead halide perovskite inks based on sub-micrometer-sized particles with tunable band gap. The particles allow the formulation of inks in benign solvents, such as propan-2-ol, and the printing of the photoactive layers of planar photoconductors with scalable, large-area coating techniques under ambient conditions. When surface traps are passivated with [6,6]-phenyl-C61-butyric acid methyl ester fullerene (PCBM), a high photoconductive gain (exceeding 200 in the blue) and reduced noise produce record-high specific detectivities exceeding 7 3 10 13 cmHz 0.5 /W and gain-bandwidth product values of 7.5 3 10 6 Hz. Given the extreme simplicity of the presented device architecture and the straightforward processing, yielding printable light detectors rivalling established technologies, the present work promises a short-term deployment of printed perovskite detectors in a multitude of opto-electronic applications.