Tailoring the interface energetics between a polymeric hole extraction layer (HEL) and a photoactive layer (PAL) in organic photovoltaics (OPVs) and organic–inorganic hybrid perovskite solar cells (PrSCs) is very important to maximize open circuit voltage (Voc), power conversion efficiency (PCE), and device lifetime.

This paper reports highly bright and efficient CsPbBr perovskite light-emitting diodes (PeLEDs) fabricated by simple one-step spin-coating of uniform CsPbBr polycrystalline layers on a self-organized buffer hole injection layer and stoichiometry-controlled CsPbBr precursor solutions with an optimized concentration. The PeLEDs have maximum current efficiency of 5.39 cd A and maximum luminance of 13752 cd m . This paper also investigates the origin of current hysteresis, which can be ascribed to migration of Br anions. Temperature dependence of the electroluminescence (EL) spectrum is measured and the origins of decreased spectrum area, spectral blue-shift, and linewidth broadening are analyzed systematically with the activation energies, and are related with Br anion migration, thermal dissociation of excitons, thermal expansion, and electron-phonon interaction. This work provides simple ways to improve the efficiency and brightness of all-inorganic polycrystalline PeLEDs and improves understanding of temperature-dependent ion migration and EL properties in inorganic PeLEDs.

mesoporous charge transfer layer, their application into the fl exible electronics would be limited due to their brittleness and the high-temperature (i.e., T > 450 °C) sintering process which damages plastic substrates. Otherwise, solutionprocessed planar heterojunction (SP-PHJ) PrSCs can be fabricated using low-temperature processable interlayers without mesoporous metal oxides; this approach enables the fabrication of fl exible PrSCs on plastic substrates. [7][8][9] Therefore, the development of a solution-processed and effi ciently charge-transporting interlayer material has been required recently to increase PCE of SP-PHJ PrSCs for the practical application of highly effi cient and fl exible PrSCs. In addition to conducting polymers (e.g., poly(3,4-ethylen edioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), [ 7,9,15,16 ] self-organized hole extraction layer (SOHEL) [ 9 ] ), several different hole transport materials (HTMs), including inorganic materials (graphene oxide, [ 17 ] reduced graphene oxide, [ 18 ] NiO x [ 15 ] ) and conjugated polymers (e.g., PolyTPD, [ 19 ] P3HT, [ 20 ] poly(2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2′,5′di(thien-2-yl)thieno[3,2-b]thiophene) (DPP-DTT), [ 21 ] PCP-DTBT, [ 21 ] and PCDTBT [ 21 ] ) have been used to increase the PCE in SP-PHJ PrSCs.Among these materials, polymeric HTMs have been intensively developed for highly effi cient SP-PHJ PrSCs because they can be fabricated by solution processing and exhibit better hole mobility compared to vacuum-processed small-molecule HTMs. [ 3 ] In the fi rst few papers reporting SP-PHJ PrSCs, they were based on the PEDOT:PSS HTM [ 16 ] because PEDOT:PSS is one of the most commonly used HTMs for organic photovoltaics [22][23][24][25][26][27] and organic light-emitting diodes (OLEDs). [ 28,29 ] However, work function (WF) of PEDOT:PSS (≈4.9-5.2 eV) is highly dependent on the ratio of the polymeric acid, PSS relative to PEDOT [ 25,28 ] and therefore may not be suffi ciently high to perfectly match the valence band maxima (VBM) of perovskite materials (e.g., -5.43 eV for methylammonium lead iodide (MAPbI 3 )) for ohmic contact and consequential effi cient charge extraction. [ 9,15,[19][20][21][22][23][24][25][26][27][28][29] Moreover, PEDOT:PSS is dispersed with a large particle size (≈60 nm) in solution; [ 30 ] it precipitates slowly from the solution during storage and is diffi cult to redisperse from the aggregated Organic-inorganic hybrid perovskite solar cells are fabricated using a watersoluble, self-doped conducting polyaniline graft copolymer based on poly(4styrenesulfonate)-g -polyaniline (PSS -g-PANI) as an effi cient hole-extraction layer (HEL) because of its advantages, including low-temperature solution processability, high transmittance, and a low energy barrier with perovskite photoactive layers. Compared with conventional poly(3,4-ethylenedioxythiop hene):poly(styrene sulfonate) (PEDOT:PSS) dispersed in water solution, PSSg-PANI molecules are dissolved in water because of the polymeric dopant covalently bonde...

Although several transparent conducting materials such as carbon nanotubes, graphene, and conducting polymers have been intensively explored as flexible electrodes in optoelectronic devices, their insufficient electrical conductivity, low work function, and complicated electrode fabrication processes have limited their practical use. Herein, a 2D titanium carbide (Ti3C2) MXene film with transparent conducting electrode (TCE) properties, including high electrical conductivity (≈11 670 S cm−1) and high work function (≈5.1 eV), which are achieved by combining a simple solution processing with modulation of surface composition, is described. A chemical neutralization strategy of a conducting‐polymer hole‐injection layer is used to prevent detrimental surface oxidation and resulting degradation of the electrode film. Use of the MXene electrode in an organic light‐emitting diode leads to a current efficiency of ≈102.0 cd A−1 and an external quantum efficiency of ≈28.5% ph/el, which agree well with the theoretical maximum values from optical simulations. The results demonstrate the strong potential of MXene as a solution‐processable electrode in optoelectronic devices and provide a guideline for use of MXenes as TCEs in low‐cost flexible optoelectronic devices.

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