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Quasi‐two‐dimensional perovskite solar cells (quasi‐2D PSCs) have drawn significant attention and are rapidly developing owing to the impressive stability of the materials and devices. However, there are no reliable guidelines for designing and selecting suitable organic spacer cations to achieve high power conversion efficiency (PCE) in quasi‐2D PSCs. Herein, the effects of the spacer cations with different substituents, i.e., benzylamine (PMA), 4‐methoxybenzylamine (p‐MeOPMA), and 4‐fluorobenzylamine (p‐FPMA), on the optoelectronic properties and device performance of quasi‐2D perovskites are systematically investigated. It is found that the spacer cations with different substituents mainly affect the crystal growth and film quality of quasi‐2D perovskites. Interestingly, quasi‐2D perovskites based on p‐MeOPMA or p‐FPMA exhibit poor crystallinity and crystal orientation, while quasi‐2D perovskite based on the unsubstituted PMA shows improved crystallinity and crystal orientation, which enables suppressed trap densities and efficient charge transport. The PMA‐based quasi‐2D perovskite (nominal n = 3) solar cell exhibits the highest PCE of 13.58%. These results demonstrate that the rational regulation of organic spacer cations plays a crucial role in improving the crystallinity and crystal orientation of perovskite films and elucidate key guiding rules for organic spacer cations for high‐performance quasi‐2D PSCs. [ABSTRACT FROM AUTHOR]

Abstract This paper elucidates the increased luminescence efficiency of CsPbBr2.1Cl0.9 sky-blue perovskite light-emitting diodes (PeLEDs) achieved through the interface modification of 3,4 ethylenedioxythiophene (PEDOT):polystyrene sulfonic acid (PSS)/quasi-two-dimensional (QTD) perovskite using CsCl and CsBr materials, respectively. QTD films were fabricated using ratios of CsPbBr2.1Cl0.9 doped with phenethylamine hydrobromide (PEABr) at 60%, 80%, and 100%. The solvent dimethyl sulfide (C2H6OS) was employed under the excitation of ambient and 365-nm laser lights. The PeLED structure was composed of Al/LiF/2,2',2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi)/CsPbBr2.1Cl0.9:PEABr/interface modification layer/PEDOT:PSS/ITO glass. The optimized results revealed that the luminance, current efficiency, and external quantum efficiency of the QTD CsPbBr2.1Cl0.9:80% PEABr PeLED with the CsCl interface modification additive was 892 cd/m2, 3.87 cd/A, and 5.56%, respectively.

In the past several years, metal‐halide perovskites have attracted much attention for their promising applications in light‐emitting diodes (LEDs). Significant progress has been made in the development of high‐efficiency green, red, and near‐infrared perovskite LEDs (PeLEDs), but blue PeLEDs are still lagging behind. Although the external quantum efficiency (EQE) of blue PeLEDs has exceeded 10%, these works mainly focus on pure blue and sky‐blue regions. Creating deep‐blue electroluminescence (EL) with high stability, efficiency, and color purity is still a great challenge for PeLEDs. Herein, deep‐blue PeLEDs are reported which have been constructed with a mixture of a quasi‐2D phase and a nanocrystal phase by introducing a small diamine cation, ethylene diammonium (EDA2+), and the effect of EDA2+ on quasi‐2D perovskite crystallization is investigated. EDA2+ with two amino ending groups has a stronger inhibitory effect on high‐n phase growth than phenylethyl ammonium, leading to the formation of small nanocrystals. Further introduction of Na+ reduces the size of the nanocrystals and broadens the band gap. Based on these improvements, deep‐blue PeLEDs with EL peaks at 467 (EQE ≈ 1.7%) and 461 nm (EQE ≈ 1.1%) are successfully constructed. Thus, this study provides a useful strategy for improving the performance of deep‐blue PeLEDs. [ABSTRACT FROM AUTHOR]

This paper elucidates the increased luminescence efficiency of CsPbBr2.1Cl0.9 sky-blue perovskite light-emitting diodes (PeLEDs) achieved through the interface modification of 3,4 ethylenedioxythiophene (PEDOT):polystyrene sulfonic acid (PSS)/quasi-two-dimensional (QTD) perovskite using CsCl and CsBr materials, respectively. QTD films were fabricated using ratios of CsPbBr2.1Cl0.9 doped with phenethylamine hydrobromide (PEABr) at 60%, 80%, and 100%. The solvent dimethyl sulfide (C2H6OS) was employed under the excitation of ambient and 365-nm laser lights. The PeLED structure was composed of Al/LiF/2,2',2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi)/CsPbBr2.1Cl0.9:PEABr/interface modification layer/PEDOT:PSS/ITO glass. The optimized results revealed that the luminance, current efficiency, and external quantum efficiency of the QTD CsPbBr2.1Cl0.9:80% PEABr PeLED with the CsCl interface modification additive was 892 cd/m2, 3.87 cd/A, and 5.56%, respectively. [ABSTRACT FROM AUTHOR]

Recently, quasi-two-dimensional (Q-2D) perovskites have received much attention due to their excellent photophysical properties. Phase compositions in Q-2D perovskites have obvious effect on the device performance. Here, efficient green perovskite light-emitting diodes (PeLEDs) were fabricated by employing o-fluorophenylethylammonium bromide (o-F-PEABr) and 2-aminoethanol hydrobromide (EOABr) as the mix-interlayer ligands. Phase compositions are rationally optimized through composition and interlayer engineering. Meanwhile, non-radiative recombination is greatly suppressed by the introduction of mix-interlayer ligands. Thus, green PeLEDs with a peak photoluminescence quantum yield (PLQY) of 81.4%, a narrow full width at half maximum (FWHM) of 19 nm, a maximum current efficiency (CE) of 27.7 cd/A, and a maximum external quantum efficiency (EQE) of 10.4% were realized. The results are expected to offer a feasible method to realize high-efficiency PeLEDs.

Quasi-two-dimensional (Q-2D) perovskites show great potential in the field of photonic and optoelectronic device applications. However, defects and local lattice dislocation still limit performance and stability improvement by nonradiative recombination, unpreferred phase distribution, and unbonded amines. Here, a low-temperature synergistic strategy for both reconstructing and solidifying the perovskite top and buried interface is developed. By post-treating the 1,4-phenylenedimethanammonium (PDMA) based (PDMA)MA 4 Pb 5 I 16 films with cesium acetate (CsAc) before thermal annealing, a condensation reaction between R-COO - and -NH 2 and ion exchange between Cs + and MA + occur. It converts the unbonded amines to amides and passivates uncoordinated Pb 2+ . Meanwhile, it adjusts film composition and improves the phase distribution without changing the out-of-plane grain orientation. Consequently, performance of 18.1% and much-enhanced stability (e.g., stability for photo-oxygen increased over 10 times, light-thermal for T 90 over 4 times, and reverse bias over 3 times) of (PDMA)MA 4 Pb 5 I 16 perovskite solar cells are demonstrated.

The quasi-two-dimensional (QTD) Cs 0.9 Rb 0.1 PbBr 2.1 Cl 0.9 :PEABr perovskite sky-blue light-emitting diode (LED) was prepared through composition engineering, doping engineering and interface modification engineering by spin coating. The PEABr organic cations were introduced into three-dimensional (3D) perovskite through content proportional control. The solution of potassium bromide (KBr) was doped in the nickel oxide (NiO x) hole injection layer and the interface between the NiO x film and the perovskite film in the device structure. The optimized luminance and external quantum efficiency (EQE) of the sky-blue LED with Cs 0.9 Rb 0.1 PBBr 2.1 Cl 0.9 : 80 % PEABr were 989 cd/m2 and 0.68 %, respectively. [ABSTRACT FROM AUTHOR]

The strategy of introducing large organic cations into three-dimensional perovskites could reduce the dimensionality of perovskites to form quasi-two-dimensional (quasi-2D) perovskites, resulting in increased stability and reduced detection limits due to less ion migration. Herein, a quasi-2D perovskite single crystal (BDA)(MA) 2 Pb 3 Br 10 (BDA = NH 3 C 4 H 8 NH 3 , MA = CH 3 NH 3 ) with a layered structure was grown by the temperature-cooling solution method. The X-ray detector based on the (BDA)(MA) 2 Pb 3 Br 10 single crystal has a sensitivity as high as 1984 μC Gy -1 cm -2 at 55.6 V/mm, and it could detect X-rays as low as 28.12 nGy s -1 at 22.2 V/mm. In addition, the X-ray imaging system based on the single-crystal device easily distinguishes between metals and plastics and exhibits a spatial resolution estimated as 250 μm, indicating the feasibility of (BDA)(MA) 2 Pb 3 Br 10 crystals for X-ray imaging. This research offers a method for the design of quasi-2D layered perovskites and enhances photoelectronic applications in X-ray inspection and imaging.

Perovskite light-emitting diodes (PeLEDs) show great potential in display and lighting because of their tunable wavelength, narrow emission bandwidths, and high color purity. Currently, the external quantum efficiency (EQE) of red and green PeLEDs has reached >23%. However, yellow PeLEDs are still rarely reported because of phase separation in mixed-halide perovskites and the coexistence of multiple phases in quasi-two-dimensional (quasi-2D) perovskites L 2 A n -1 B n X 3 n +1 ( n = 1, 2, 3, ...), where L is a bulky organoammonium ligand. Here, we fabricate stable yellow PeLEDs by manipulating the phase distribution and incorporating rubidium cations (Rb + ) in quasi-2D perovskites. The transient absorption results confirm that alkylammonium ligand butyl ammonium (BA) has a narrower phase distribution than phenylethyl ammonium (PEA) in the quasi-2D perovskites, resulting in a more blue-shifted emission peak. We further incorporate a proper molar ratio of Rb + in the (BA) 2 CsPb 2 I 7 perovskite to blue-shift the emission peak to the yellow range. Finally, the yellow PeLEDs exhibit an EQE of 3.5%, and the stable emission peak is located at 595 nm. Our work provides a useful approach for the fabrication of highly efficient and stable yellow PeLEDs.

Recently, quasi-two-dimensional (Q-2D) perovskites have received much attention due to their excellent photophysical properties. Phase compositions in Q-2D perovskites have obvious effect on the device performance. Here, efficient green perovskite light-emitting diodes (PeLEDs) were fabricated by employing o-fluorophenylethylammonium bromide (o-F-PEABr) and 2-aminoethanol hydrobromide (EOABr) as the mix-interlayer ligands. Phase compositions are rationally optimized through composition and interlayer engineering. Meanwhile, non-radiative recombination is greatly suppressed by the introduction of mix-interlayer ligands. Thus, green PeLEDs with a peak photoluminescence quantum yield (PLQY) of 81.4%, a narrow full width at half maximum (FWHM) of 19 nm, a maximum current efficiency (CE) of 27.7 cd/A, and a maximum external quantum efficiency (EQE) of 10.4% were realized. The results are expected to offer a feasible method to realize high-efficiency PeLEDs., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The handling Editor declared a past co-authorship with one of the authors SS., (Copyright © 2022 Wang, Meng, Feng, Shi, Qiu, Sun, Chen, Zeng, Zhu and Su.)

Quasi-two-dimensional (Q-2D) perovskites featured with multidimensional quantum wells (QWs) have been the main candidates for optoelectronic applications. However, excessive low-dimensional perovskites are unfavorable to the device efficiency due to the phonon-exciton interaction and the inclusion of insulating large organic cations. Herein, the formation of low-dimensional QWs is suppressed by removing the organic cation 1-naphthylmethylamine iodide (NMAI) through ultrahigh vacuum (UHV) annealing. Perovskite light-emitting diode (PLED) devices based on films annealed with optimized UHV conditions show a higher external quantum efficiency (EQE) of 13.0% and wall-plug efficiency of 11.1% compared to otherwise identical devices with films annealed in a glovebox.