Organic-inorganic lead halide perovskite is emerging as a potential emissive material for light emitting devices, such as, light emitting diodes (LEDs) and lasers, which has emphasized the necessity of understanding its fundamental opto-physical properties. In this work, the temperature-dependent photoluminescence of CHNHPbBr perovskite quantum dots (QDs), polycrystalline thin film (TF), and single crystal (SC) has been studied. The optophysical properties, such as exciton-phonon scattering, exciton binding energy, and exciton decay dynamics, were investigated. The exciton-phonon scattering of perovskite is investigated, which is responsible for both PL line width broadening and nonradiative decay of excitons. The exciton binding energy of QDs, TF, and SC were estimated to be 388.2, 124.3, and 40.6 meV, respectively. The observed main exciton decay pathway for QDs is the phonon assisted thermal escape, while that for TF and SC was the thermal dissociation due to low exciton binding energy.

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.

Recently, all-inorganic perovskite quantum dots (PeQDs), CsPbX 3 have become attractive because of their excellent optoelectronic properties and superior air/moisture stabilities compared with conventional organic−inorganic hybrid perovskites, and the application of CsPbX 3 PeQDs to light-emitting devices (LEDs) has also become competitive. To enable the use of CsPbX 3 PeQDs for thin-film-type perovskite quantum-dot LEDs (PeQLEDs), a paradox associated with the ligand property and surface passivation must be overcome during thin-film fabrication. A decline in the photoemission performance was observed at relatively low amounts of surface-passivating ligands, while the quality of the thin film deteriorated in the presence of excessive ligands. To address this conflict, in this study, the performance of PeQLEDs based on CsPbX 3 fabricated by a novel method involving solid-state ligand exchange (SLE) with aromatic acid/amine was investigated. Using this strategy, most of the excess ligands were removed while preserving the surface passivation of CsPbX 3 in the thin film. We discovered that an optimal aromatic acid/amine ligand ratio is required for CsPbX 3 -based PeQLEDs to retain the solubility of the PeQDs and simultaneously accomplish the SLE process without affecting the properties of the PeQD. Moreover, an improvement in the overall photoemission efficiency of the resulting PeQLED device was confirmed under red, green, and blue conditions. In addition, a luminance of 1889 cd/m 2 and a current efficiency of 6.28 cd/A was achieved for the PeQLED.

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.

The paired electric dipole layers significantly intensify the built-in field across the perovskite layer, resulting in suppressed charge trapping of photogenerated charges.

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International audienceA comprehensive experimental study is reported on the optical and electrical characteristics of 2-((5-(4-(diphenylamino)phenyl)thiophen-2-yl)methylene)malononitrile (DPTMM) when used as molecular donor in an organic solar cell (OSC) device structure. A major property of this new donor-type material is an unusually deep highest-occupied molecular orbital (HOMO) level that leads to a high open-circuit voltage (Voc). A reasonably high hole-mobility was also observed in a hole-injection diode configuration. These are both promising factors for high-performance OSCs. In order to fully explore the potential of DPTMM in bulk-heterojunction-based OSCs, a step-wise experimental strategy was applied to optimize film composition and cell architecture. By co-evaporating the DPTMM with C60 to promote exciton dissociation by maximizing the heterojunction area power conversion efficiency (PCE) of 3.0% was achieved. Finally, inserting a buffer layer and a spatial gradient of the donor/acceptor ratio was found to provide better conduction paths for charge carriers. The maximum obtained PCE was 4.0%, which compares favorably with the state-of-the-art of high-performance OSCs. All optimized devices show quite unusual high Voc values up to 1 V

SignificancePhotovoltaics (PVs) benefitting from ferroelectric polarizations can overcome critical limitations of conventional type PVs. In this class, Bi2FeCrO6 is known to be the best-performing material; however, a fundamental understanding of the origin is lacking, which has limited further performance improvements. Here, we carried out a theoretical investigation of the electronic structure of this material. As a result, electron−hole (e-h) pairs are observed to separate upon photoexcitation, which can be a dominant underlying mechanism for the exceptional PV responses. Based on this understanding, we further suggest five novel materials that can offer a combination of strong e-h separations and visible-light absorptions. We expect the community of ferroelectric PVs to immediately benefit from the features of the new suggested materials.