We describe the synthesis and preliminary photovoltaic performance of a solution-processable organic small-molecule electron donor DT-DPP(TVT)2 that consists of dithienyldiketopyrrolopyrrole (DT-DPP) as the core and thienylvinylthiophene (TVT) as the endgroups. The new compound is a crystalline solid with a Tm of approximately 216°C. Cyclic voltammetry indicates that DT-DPP(TVT)2 exhibits two quasi-reversible one-electron oxidation waves at ca. 0.68 and 0.90 V versus an Ag/AgCl reference electrode, respectively, leading to an estimated highest occupied molecular orbital (HOMO) level of about −5.08 eV. Introducing the branched 2-hexyldecyl side chain provides DT-DPP(TVT)2 with a high solubility in chloroform up to ca. 36 mg mL−1 at room temperature. Thermal annealing increases the crystallinity of the as-cast film from chloroform solution, thereby rendering slightly red-shifted charge-transfer absorption maxima. Fitting the space-charge-limited current characteristics of the thermally annealed thin film yields an improved hole mobility of ∼2.14×10−4 cm2 V−1 s−1 at low voltages versus ∼1.46×10−4 cm2 V−1 s−1 of the as-cast film. A first characterization of the solar cell [ITO/PEDOT: PSS/DT-DPP(TVT)2: PC61BM/Al] produces a power conversion efficiency of ∼3% with VOC≈0.78 V, JSC≈7.91 mA cm−2, and FF≈48.7%, under simulated AM1.5G with an illumination intensity of 100 mW cm−2. It should be noted that the thermal effect on the thin film absorption of DT-DPP(TVT)2 does not seem to be completely similar to the molecular donor DPP(TFNa)2 reported earlier, which bears 6-fluoronaphthyl endgroups.
We report a flexible amorphous Lanthanide doped In-Zn-O (IZO) thin-film transistor (TFT) backplane on polyimide
(PI) substrate. In order to de-bond the PI film from the glass carrier easily after the flexible AMOLED process, a
special inorganic film is deposited on the glass before the PI film is coated. The TFT exhibited a field-effect
mobility of 6.97 cm2V-1 s-1, a subthreshold swing of 0.248 V dec-1, and an Ion/Ioff ratio of 5.19×107, which is
sufficient to drive the OLEDs.
The synthesis of new small-molecule amine compounds is presented. The triamino derivative with ethyl substituents
possesses better processability in alcoholic solvent and was utilized as an electron-injection layer in organic light-emitting diodes (OLEDs) in order to avoid interlayer mixing. The performance of the resulting OLEDs that consisted of
an Al cathode and a solution-processed molecular green-emitting layer is shown to depend on the thickness of the small-molecule electron-injection interlayer and is preliminarily discussed.
Efficient deep blue-emitting poly[9,9-bis(2-ethylhexyl)fluorene] derivatives were synthesized via incorporating 2,8-diyl-dibenzothiophene-S,S-dioxide (FSO) moiety into polyfluorene backbone. The photoluminescence (PL) spectra exhibit excellent thermal stability and PL quantum efficiencies distinctly improved upon thermal annealing at various temperatures. Spectrally stable light-emitting diodes were obtained based on resulting copolymers at various driving voltages and operation times. The best device performances were achieved based on copolymer PF-FSO10, which shows a maximum external quantum efficiency of 1.78%, and 2.27% upon thermal annealing in the air, and as high as 3.52% by inserting an additional electron injection layer poly(9,9-bis(6′-(bromilamino)hexyl))fluorene (PFNBr) between the polymer-cathode interface. The stable electroluminescence spectra with CIE coordinates of (0.16, 0.08) and superior device performances indicates that the copolymers could be a promising candidate of deep blue emitters in full-color displays.
We report the synthesis and photovoltaic properties of poly[2,7-(9,
9-di-n-octyl-silafluorene)-alt-5,5''-(4',
7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PSiF-DBT). The polymer heterojunction solar cells fabricated from PSiF-DBT as the electron
donor blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor exhibited a high powerconversion
efficiency up to 5.4% with an open-circuit voltage of 0.90 V, a short-circuit current density of 9.5 mA cm-2
and a fill factor of 50.7% under the illumination of AM 1.5 G from a solar simulator (800 W m-2). A comparative study
between PSiF-DBT and its polyfluorene analogous PFDTBT and PFO-DBT demonstrates that the high performance of
PSiF-DBT originated from its red-shifted absorption spectrum up to 680 nm and high mobility of 1 × 10-3 cm2 V-1 s-1 compared with 645 nm and 3 × 10-4 cm2
V-1 s-1 for corresponding polyfluorene derivatives, respectively. These results indicate polysilafluorene derivatives are a promising new class of donor materials for polymer solar cells.
A series of saturated red emission copolymers, polyfluorene copolymers (PFO-DBT), were synthesized and
characterized. The saturated red EL emission from the copolymer peaking at about 677 nm and electroluminescence
(EL) efficiency of 1.4% based on simple device structure of ITO/PEDOT/PFO-DBT/Ba/Al, were achieved. The
operation mechanism of the device was discussed and it was found that hole carrier injection is the major obstacle for
improving EL efficiency and EL stability. To overcome such problem, we utilized MEH-PPV which has low HOMO
level blended with the PFO-DBT copolymer to improve EL efficiency to 1.7%. Simultaneously, the EL emission lifetime
of the device with PFO-DBT:MEH-PPV (50:50) blended polymer extended to 2000hrs. Monochrome passive red
emission displays with the blended polymer were fabricated, and exhibited excellent pictures.
White polymer light-emitting diodes (WPLEDs) with bilayer structure were fabricated by spin coating method. The device structure used here is ITO/PEDOT:PSS/blend1/blend2/Ba/Al, where blend1 consists of poly(N-vinylcarbazole) (PVK) and copolymer of 9,9-diotylfluorene and 4,7-di(3-hexyl-thien-2-yl)-2,1,3-benzothiadiazole (PFO-DHTBT), and blend2 is the blend of polyhedral oligomeric silsesquioxane-terminated poly(9,9-dioctylfluorene) (PFO-poss) and phenyl-substituted PPV derivative (P-PPV). The copolymer PFO-DHTBT emits red light. The blend2 gives off both green and blue emission bands in electroluminescence (EL) spectrum. the relative intensity of the bands depends on the blend ratios. The EL spectrum of the device can be controlled by respectively adjusting the weight ratios in the blend1 and blend2, thickness as well. At the weight ratios of 100:3 (PVK:PFO-DHTBT) in blend1 and 100:1 (PFO-poss: P-PPV) in blend2, and with keeping the thickness of the two blend films to be 40nm, the white fluorescent light emission with Commission International De L'Eclairage (CIE) coordinates of (0.33, 0.32) is achieved in a large voltage range, the maximal quantum and luminance efficiencies of 3% (ph/eh) and 4.4cd/A are obtained at 6.1V, and the maximal luminance is 6300cd/m2 at 10V.
The process of electroluminescence (EL) decay of devices made by a trivalent europium (Eu) complex, Eu(DBM)3(phen)(DBM=dibenzoylmethane, phen=phenanthroline), dispersed in poly(N-vinycarbazole) (PVK), has been studied. The decay process exhibits the characteristics of the time constant being independent of the intensity of pulsed drive voltage and the EL intensity having nearly single exponential dependence on the decay time. The decay process is considered as the monomolecular recombination process. By analyzing the process, we believe that the charged carrier concentrations (involving both holes and electrons) at initial state (the decay time t=o) do not influence the time constant, indicating that injected holes and electrons within PVK film are of unbalance seriously. From this point of view, we discussed an efficient device based on Eu(DBM)3 (phen) dispersed in polymer structure.
In organic thin film electroluminescence device with ITO/PPV/TPD:CuPc/Alq:DCMl/Al structure, the TPD:CuPc Langmuir-Blodgett (LB) film as electron-blocking layer was inserted between PPV and Alq:DCMl layer. A device without TPD:CuPc layer or a device with monolayer of TPD:CuPc which was applied at higher DC voltage exhibited EL emission from both the PPV and Alq:DCMl layers. Whereas a device with monolayer of TPD:CuPc layer which was applied at lower voltage or a device with double layers of TPD:CuPc had an EL emission only from Alq:DCMl layer implying that the TPD:CuPc layer can effectively block the electrons and the Alq:DCMl electron transport layer worked as the emitting layer. Hence, we can spatially control the recombination zone and obtain different EL emission by adjusting the thickness of carrier blocking layer.
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