Electronic Level Alignment at an Indium Tin Oxide/PbI₂ Interface and Its Applications for Organic Electronic Devices

The electronic level alignment at the indium tin oxide (ITO)/PbI₂ interface is investigated by an ultraviolet photoelectron spectroscopy. An n-type conductivity property is found for PbI₂ as well as a downward shift energy level at the ITO/PbI₂ interface. These indicate that PbI₂ can be used as an anode buffer layer for organic electronic devices. The power conversion efficiency of the organic solar cell based on tetraphenyldibenzoperiflanthene/C₇₀ planar heterojunction is dramatically increased from 1.05 to 3.82%. Meanwhile, the thermally activated delayed fluorescence organic light-emitting diode based on 4,4′,4″-tri­(<i>N</i>-carbazolyl)­triphenylamine–((1,3,5-triazine-2,4,6-triyl)­tris­(benzene-3,1-diyl))­tris­(diphenylphosphine oxide) shows a significantly reduced turn-on voltage and enhanced power efficiency from 6.26 to 18.60 lm/W. The improved performance is attributed to the high hole injection/extraction efficiency at the ITO/PbI₂ interface. Besides, the near-infrared (NIR) absorption of lead phthalocyanine (PbPc)-based NIR organic photodetector (NIR-OPD) is dramatically increased, indicating that the PbI₂ layer can also be used as a template layer for the growth of the triclinic phase of PbPc. As a result, the optimized device shows an external quantum efficiency of 26.7% and a detectivity of 9.96 × 10¹¹ jones at 900 nm, which are among the highest ones reported for organic NIR-OPDs

Surface Plasmon Enhanced Organic Solar Cells with a MoO₃ Buffer Layer

High-efficiency surface plasmon enhanced 1,1-bis-(4-bis­(4-methyl-phenyl)-amino-phenyl)-cyclohexane:C70 small molecular bulk heterojunction organic solar cells with a MoO₃ anode buffer layer have been demonstrated. The optimized device based on thermal evaporated Ag nanoparticles (NPs) shows a power conversion efficiency of 5.42%, which is 17% higher than the reference device. The improvement is attributed to both the enhanced conductivity and increased absorption due to the near-field enhancement of the localized surface plasmon resonance of Ag NPs

High-Performance Organic Small-Molecule Panchromatic Photodetectors

High-performance panchromatic organic photodetectors (OPDs) containing small molecules lead phthalocyanine (PbPc) and C₇₀ fullerene as donor and acceptor, respectively, were demonstrated. The OPDs had either a PbPc/C₇₀ planar heterojunction (PHJ) or a PbPc/PbPc:C₇₀/C₇₀ hybrid planar-mixed molecular heterojunction (PM-HJ) structure. Both the PHJ and the PM-HJ devices showed a broad-band response that covered wavelengths from 300 to 1100 nm. An external quantum efficiency (EQE) higher than 10% and detectivity on the order of 10¹² Jones were obtained in the wavelength region from 400 to 900 nm for the PHJ device. The EQE in the near-infrared region was enhanced by using the PM-HJ device structure, and a maximum EQE of 30.2% at 890 nm was observed for the optimized device with a 5% PbPc-doped C₇₀ layer. Such an EQE is the highest at this wavelength of reported OPDs. The detectivity of the PM-HJ devices was also higher than that of the PHJ one, which is attributed to the increased efficiency of exciton dissociation in bulk heterojunction structure, increased absorption efficiency caused by formation of triclinic PbPc in the PbPc:C₇₀ mixed film when it was deposited on a pristine PbPc layer, and high hole mobility of the PbPc-doped C₇₀ layer

Efficient Triplet Application in Exciplex Delayed-Fluorescence OLEDs Using a Reverse Intersystem Crossing Mechanism Based on a Δ<i>E</i>_S–T of around Zero

We demonstrate highly efficient exciplex delayed-fluorescence organic light-emitting diodes (OLEDs) in which 4,4′,4″-tris­[3-methylphenyl­(phenyl)­aminotriphenylamine (m-MTDATA) and 4,7-diphenyl-1,10-phenanthroline (Bphen) were selected as donor and acceptor components, respectively. Our m-MTDATA:Bphen exciplex electroluminescence (EL) mechanism is based on reverse intersystem crossing (RISC) from the triplet to singlet excited states. As a result, an external quantum efficiency (EQE) of 7.79% at 10 mA/cm² was observed, which increases by 3.2 and 1.5 times over that reported in <i>Nat. Photonics</i> <b>2012</b>, <i>6</i>, 253 and <i>Appl. Phys. Lett.</i> <b>2012</b>, <i>101</i>, 023306, respectively. The high EQE would be attributed to a very easy RISC process because the energy difference between the singlet and triplet excited states is almost around zero. The verdict was proven by photoluminescence (PL) rate analysis at different temperatures and time-resolved spectral analysis. Besides, the study of the transient PL process indicates that the presence of an unbalanced charge in exciplex EL devices is responsible for the low EQE and high-efficiency roll-off. When the exciplex devices were placed in a 100 mT magnetic field, the permanently positive magnetoelectroluminescence and magnetoconductivity were observed. The magnetic properties confirm that the efficient exciplex EL only originates from delayed fluorescence via RISC processes but is not related to the triplet–triplet annihilation process