6 Search Results

Perovskite light–emitting diodes (PeLEDs) have received great attention for their potential as next–generation display technology. While remarkable progress has been achieved in green, red, and near–infrared PeLEDs with external quantum efficiencies (EQEs) exceeding 20%, obtaining high performance blue PeLEDs remains a challenge. Poor charge balance due to large charge injection barriers in blue PeLEDs has been identified as one of the major roadblocks to achieve high efficiency. Here band edge control of perovskite emitting layers for blue PeLEDs with enhanced charge balance and device performance is reported. By using organic spacer cations with different dipole moments, that is, phenethyl ammoniummore » (PEA), methoxy phenethyl ammonium (MePEA), and 4–fluoro phenethyl ammonium (4FPEA), the band edges of quasi–2D perovskites are tuned without affecting their band gaps. Furthermore, detailed characterization and computational studies have confirmed the effect of dipole moment modification to be mostly electrostatic, resulting in changes in the ionization energies of ≈0.45 eV for MePEA and ≈ –0.65 eV for 4FPEA based thin films relative to PEA–based thin films. With improved charge balance, blue PeLEDs based on MePEA quasi–2D perovskites show twofold increase of the EQE as compared to the control PEA based devices.« less

Abstract Surface passivation of perovskite solar cells (PSCs) using a low‐cost industrial organic pigment quinacridone (QA) is presented. The procedure involves solution processing a soluble derivative of QA, N , N ‐bis(tert‐butyloxycarbonyl)‐quinacridone (TBOC‐QA), followed by thermal annealing to convert TBOC‐QA into insoluble QA. With halide perovskite thin films coated by QA, PSCs based on methylammonium lead iodide (MAPbI ₃ ) showed significantly improved performance with remarkable stability. A PCE of 21.1 % was achieved, which is much higher than 18.9 % recorded for the unmodified devices. The QA coating with exceptional insolubility and hydrophobicity also led to greatly enhanced contact angle frommore » 35.6° for the pristine MAPbI ₃ thin films to 77.2° for QA coated MAPbI ₃ thin films. The stability of QA passivated MAPbI ₃ perovskite thin films and PSCs were significantly enhanced, retaining about 90 % of the initial efficiencies after more than 1000 hours storage under ambient conditions.« less

Abstract Surface passivation of perovskite solar cells (PSCs) using a low‐cost industrial organic pigment quinacridone (QA) is presented. The procedure involves solution processing a soluble derivative of QA, N , N ‐bis(tert‐butyloxycarbonyl)‐quinacridone (TBOC‐QA), followed by thermal annealing to convert TBOC‐QA into insoluble QA. With halide perovskite thin films coated by QA, PSCs based on methylammonium lead iodide (MAPbI ₃ ) showed significantly improved performance with remarkable stability. A PCE of 21.1 % was achieved, which is much higher than 18.9 % recorded for the unmodified devices. The QA coating with exceptional insolubility and hydrophobicity also led to greatly enhanced contact angle frommore » 35.6° for the pristine MAPbI ₃ thin films to 77.2° for QA coated MAPbI ₃ thin films. The stability of QA passivated MAPbI ₃ perovskite thin films and PSCs were significantly enhanced, retaining about 90 % of the initial efficiencies after more than 1000 hours storage under ambient conditions.« less

Tin halide perovskites and perovskite-related materials have emerged as promising lead-free hybrid materials for various optoelectronic applications. While remarkable progress has been achieved in the development of organic tin halide hybrids with diverse structures and controlled dimensionalities at the molecular level, some controversial results that have been reported recently need to be addressed. For instance, different photophysical properties have been reported for two-dimensional (2D) (PEA)₂SnBr₄ (PEA = phenylethylammonium) by several groups with distinct emission peaks at around 468 and 550 nm. Here we report our efforts in the synthesis of phenylethylammonium tin bromide hybrids with zero-dimensional (0D) and 2D structures,more » and characterizations of their structural and photophysical properties. 0D [(PEA)₄SnBr₆][(PEA)Br]₂[CCl₂H₂]₂ was found to exhibit strong yellow emission peak at 566 nm with a photoluminescence quantum efficiency (PLQE) of ~90%, while 2D (PEA)₂SnBr₄ had weak emission peak at 470 nm with a PLQE of <0.1%. Interestingly, 0D [(PEA)₄SnBr₆][(PEA)Br]₂[CCl₂H₂]₂ can be converted into 2D (PEA)₂SnBr₄ upon drying, which would return to 0D [(PEA)₄SnBr₆][(PEA)Br]₂[CCl₂H₂]₂ upon addition of dichloromethane. Powder X-ray diffraction results confirmed the reversible transformation between 0D and 2D structures. Density functional theory calculations showed that excitons in 0D [(PEA)₄SnBr₆][(PEA)Br]₂[CCl₂H₂]₂ are highly localized, resulting in a strongly Stokes shifted broadband emission, while delocalized electronic states in 2D (PEA)₂SnBr₄ result in weaker exciton binding, a higher exciton mobility, and a higher nonradiative decay.« less

Zero-dimensional (0D) organic metal halide hybrids are an emerging class of light emitting materials with exceptional photoluminescence quantum efficiencies (PLQEs), thanks to their perfect “host–guest” structures with light emitting metal halide species periodically “embedded” in a wide band gap organic cationic matrix through ionic bonds. However, achieving efficient blue emissions is challenging for this class of materials, as structural distortions of metal halides often lead to large Stokes shifts. Here we report a highly luminescent blue emitting 0D organic lead bromide, (C₁₃H₁₉N₄)₂PbBr₄, with a peak emission of 460 nm (2.70 eV), a full width at half maximum (FWHM) of 66more » nm (0.40 eV), a Stokes shift of 111 nm (0.85 eV), and a PLQE of ~40%. Single crystal structure analysis shows that individual PbBr₄^2– species adopt a near-seesaw structure, which are coordinated to benzyl-hexamethylenetetrammonium (C₁₃H₁₉N₄⁺) organic cations. The relatively small Stokes shift as compared to those of previously reported 0D organic metal halide hybrids are attributed to the low chemical reactivity of Pb 6s² lone pairs and the rigid organic cationic matrix. Finally, (C₁₃H₁₉N₄)₂PbBr₄ also shows exceptional stability in air with little-to-no change of properties for more than a year in ambient conditions.« less

Organic-inorganic metal halide hybrids are an important class of crystalline materials with exceptional structural and property tunability. Recently metal halide perovskites with ABX₃ structure have been extensively investigated as new generation semiconductors for various optoelectronic devices, including photovoltaic cells, light emitting diodes, photodetectors, and lasers, for their exceptional optical and electronic properties. By controlling the morphological dimensionality, low dimensional metal halide perovskites, including 2D perovskite nanoplatelets, 1D perovskite nanowires, and 0D perovskite quantum dots, have been developed to exhibit distinct properties from their bulk counterparts, due to quantum size effects. Besides ABX₃ perovskites, organic-inorganic metal halide hybrids, containing the samemore » fundamental building block of metal halide octahedra (BX₆), can also be assembled to possess other types of crystallographic structures. Using appropriate organic and inorganic components, low dimensional organic-inorganic metal halide hybrids with 2D, quasi-2D, corrugated-2D, 1D, and 0D structures at the molecular level have been developed and studied. Due to the strong quantum confinement and site isolation, these low dimensional metal halide hybrids at the molecular level exhibit remarkable and unique properties that are significantly different from those of ABX₃ perovskites. In light of the rapid development of low dimensional metal halide perovskites and hybrids, it is indeed timely to review the recent progress in these areas. Also, there is a need to clarify the difference between morphological low dimensional metal halide perovskites and molecular level low dimensional metal halide hybrids, as currently the terminologies of low dimensional perovskites are not appropriately used in many cases. Finally, in this review article, we discuss the synthesis, characterization, application, and computational studies of low dimensional metal halide perovskites and hybrids.« less