Planar heterojunction organic photovoltaic cells based on tetramethyl substituted copper(II) phthalocyanine treated with thermal annealing

© 2014 IOP Publishing Ltd. The fabrication of planar heterojunction (PHJ) organic photovoltaic (OPV) cells using tetramethyl substituted copper(II) phthalocyanine (CuMePc) as an electron donor and C60as an acceptor is described. The impact of post-fabrication thermal annealing upon the performance of these cells has been examined. Atomic force microscopy (AFM) images and UV-visible absorption spectra of CuMePc thin films revealed crystallization of CuMePc induced by thermal annealing at 190°C. The crystallized CuMePc films accounted for improved hole mobility, broadened absorption spectrum, and increased donor/acceptor interface in the as-fabricated cells after thermal annealing. AFM images also revealed that the surface of MoO3film was smooth and close-packed after thermal annealing, which efficiently blocked the leakage current in the annealed cells, leading to dramatic improvement of performance for the PHJ cells using CuMePc as the electron donor and MoO3or V2O5as the anode buffer layer. The power conversion efficiency of the thermal-annealed PHJ cell with a configuration of ITO/MoO3/CuMePc/C60/Bathocuproine/Al was higher than that of the bulk heterojunction (BHJ) cell fabricated by co-depositing CuMePc and C60. It was mainly because the isolated clusters of CuMePc and/or C60molecules formed during the fabrication of the BHJ cell was avoided in the PHJ cell.Link_to_subscribed_fulltex

CsPb(Br/Cl)3 Perovskite Nanocrystals with Bright Blue Emission Synergistically Modified by Calcium Halide and Ammonium Ion

Colloidal cesium lead halide (CsPbX3, X = Cl, Br, and I) perovskite nanocrystals (NCs) demonstrate supreme optical properties in the spectra region of infrared, red, and green. High-performance blue-emitting counterparts are still eagerly required for next-generation full-color displays. However, it is challenging to obtain efficient blue perovskite NCs, especially in a deep blue region with an emission wavelength of around 460 nm or shorter. Herein, calcium halide and ammonium ions are applied simultaneously to modify the CsPb(Br/Cl)3 NCs in situ to reduce surface defects, finally remarkably enhancing the photoluminescence quantum yield (PLQY) from 13% to 93% with an emission peak at 455 nm and the Commission Internationale de l’Eclairage (CIE) coordinates at (0.147, 0.030), which is close to the requirement of the Rec.2020 standard and also meets the requirement of blue emission in DCI-P3. Bright white emission and a wide color gamut are also achieved by combining the commercial red-emitting and green-emitting phosphors. The combination of time-resolved PL spectra and femtosecond transient absorption results discloses the reason for PLQY improvement as suppressing the nonradiative recombination

Unraveling the Position Effect of Spiroxanthene-Based n-Type Hosts for High-Performance TADF–OLEDs

For developing high-performance organic light-emitting diodes (OLEDs) with thermally activated delayed fluorescent (TADF) emitters, the diphenyltriazine (TRZ) unit was introduced onto the 2′- and 3′-positions of xanthene moiety of spiro[fluorene-9,9′-xanthene] (SFX) to construct n-type host molecules, namely 2′-TRZSFX and 3′-TRZSFX. The outward extension of the TRZ unit, induced by the meta-linkage, resulted in a higher planarity between the TRZ unit and xanthene moiety in the corresponding 3′-TRZSFX. Additionally, this extension led to a perched T1 level, as well as a lower unoccupied molecular orbital (LUMO) level when compared with 2′-TRZSFX. Meanwhile, the 3′-TRZSFX molecules in the crystalline state presented coherent packing along with the interaction between TRZ units; the similar packing motif was spaced apart from xanthene moieties in the 2′-TRZSFX crystal. These endowed 3′-TRZSFX superior electron transport capacity in single-carrier devices relative to the 2′-TRZSFX-based device. Hence, the 3′-TRZSFX-based TADF–OLED showed remarkable electroluminescent (EL) performance under the operating luminance from turn-on to ca. 1000 cd·m−2 with a maximum external quantum efficiency (EQEmax) of 23.0%, thanks to its matched LUMO level with 4CzIPN emitter and better electron transport capacity. Interestingly, the 2′-TRZSFX-based device, with an EQEmax of 18.8%, possessed relatively low roll-off and higher efficiency when the operating luminance exceeded 1000 cd·m−2, which was attributed to the more balanced carrier transport under high operating voltage. These results were elucidated by the analysis of single-crystal structures and the measurements of single-carrier devices, combined with EL performance. The revealed position effect of the TRZ unit on xanthene moiety provides a more informed strategy to develop SFX-based hosts for highly efficient TADF–OLEDs