A Silanol-Functionalized Polyoxometalate with Excellent Electron Transfer Mediating Behavior to ZnO and TiO 2 Cathode Interlayers for Highly Efficient and Extremely Stable Polymer Solar Cells

Combining high efficiency and long lifetime under ambient conditions still poses a major challenge towards commercialization of polymer solar cells. Here we report a facile strategy that can simultaneously enhance the efficiency and temporal stability of inverted photovoltaic architectures. Inclusion of a silanol-functionalized organic–inorganic hybrid polyoxometalate derived from a PW9O34 lacunary phosphotungstate anion, namely (nBu4N)3[PW9O34(tBuSiOH)3], significantly increases the effectiveness of the electron collecting interface, which consists of a metal oxide such as titanium dioxide or zinc oxide, and leads to a high efficiency of 6.51% for single-junction structures based on poly(3-hexylthiophene):indene-C60 bisadduct (P3HT:IC60BA) blends. The above favourable outcome stems from a large decrease in the work function, an effective surface passivation and a decrease in the surface energy of metal oxides which synergistically result in the outstanding electron transfer mediating capability of the functionalized polyoxometalate. In addition, the insertion of a silanol-functionalized polyoxometalate layer significantly enhances the ambient stability of unencapsulated devices which retain nearly 90% of their original efficiencies (T90) after 1000 hours

A water soluble inorganic molecular oxide as a novel efficient electron injection layer for hybrid light-emitting diodes (HyLEDs)

We demonstrate that electron injection in single-layer polyfluorene based polymer light-emitting diodes (PLEDs) can be significantly enhanced by inserting a thin (&lt;10 nm) inorganic polyoxometalate (POM) molecular oxide layer between the polymer layer and an aluminum cathode. Hydrophilic POM was spin-cast from methanol, an orthogonal solvent with regard to the hydrophobic polymer layer underneath, to form the thin cathode interfacial/electron injection layer. A lower turn-on and operating voltage and a higher luminance and current density was obtained in the POM-modified hybrid LEDs (HyLEDs) which are associated with the electron injection barrier reduction in the modified polymer/Al interface, evidenced by the increased open circuit voltage from photovoltaic measurements. These results demonstrate the potential of polyoxometalates as novel, stable cathode interfacial layers for efficient electron injection/transport in high performance HyLEDs.</p

Effect of triphenylsulfonium triflate addition in wide band-gap polymer light-emitting diodes: improved charge injection, transport and electroplex-induced emission tuning

The presence of mobile anions in the emitting layer of polymer-based OLEDs has been proven to influence substantially the injection characteristics of the diode. In this work we report on the improvement of both injection and transport of charge carriers in blue emitting poly[2-(6-cyano-6-methyl-heptyloxy)-1,4- phenylene] (CN-PPP) based OLEDs upon insertion of the all-organic triphenylsulfonium (TPS) triflate salt in the emitting layer. On one hand, the anion displacement influences the energetics at the polymer/anode interface facilitating hole injection, whereas, on the other hand, the triphenylsulfonium cations act as electron transporting sites. The OLEDs exhibit significantly reduced turn-on voltage to half their initial value and increased luminance at low operating voltage. Moreover, the large energetic mismatch of the polymer and the triphenylsulfonium salt as well as the polarity induced by the ions result in simultaneous dual emission originating from the polymer exciton and from an electroplex, which is proposed to be formed at the triphenylsulfonium salt/polymer interfaces in the bulk. These results show that triphenylsulfonium salts represent an attractive class of materials that can be blended with conjugated polymers and can modify their electrical and/or emissive characteristics.</p

Incorporating triphenyl sulfonium salts in polyfluorene PLEDs: an all-organic approach to improved charge injection

All-organic sulfonium salts are introduced as a class of ionic compounds that show high compatibility with conjugated polymers and may form blends with attractive luminescent properties leading to significant improvement in single-layer polymer light emitting diodes' (PLEDs') performance. We demonstrate that triphenylsulfonium (TPS) triflate:polyfluorene-co-benzothiadiazole (F8BT)-blend based PLEDs show a lower turn-on voltage, an increased luminous efficiency and higher peak luminance values. These results are being rationalized in terms of anionic accumulation and space charge formation at the anode side, which facilitates hole injection, leading to more balanced injection and subsequently to a higher recombination rate. Moreover, we find that the salt anion size plays a critical role in the device operating characteristics. The judicious choice of both the salt and the emitting polymer by considering relative energy level alignment, salt electrochemical stability and acquired thermodynamic stability of blend morphology is important for the achievement of high performance PLEDs without requiring elaborate device architectures.</p

Influence of the anion on the optoelectronic characteristics of triphenylsulfonium salts modified polymer light emitting devices

Triphenylsulfonium salts addition in the emitting layer of polymer light emitting diodes (PLEDs) has been shown to be beneficial for charge injection and transport due to both ionic effects and π-conjugation in the phenyl rings of the cation. In some cases the emission profile can be also modified through an electroplex formation. Herein we investigate the effect of four TPS-salts with different counter anions on the overall PLED performance upon blending each salt with the conjugated polymer poly[2-(6-cyano-6-methyl-heptyloxy)-1,4-phenylene] (CN-PPP). In particular, three perfluoroalkanesulfonate organic anions of increasing size (triflate, nonaflate, PFOS) and a perfluorinated inorganic anion (SbF6) are compared. It is shown that the anion size affects primarily the turn-on and operational voltage, whereas its chemical nature is crucial for achieving high luminance values. The counteranion exerts also a direct impact on the dispersion properties of the salt in the polymer matrix, and thus, the film morphology, which in turn influences the emission colour and efficiency of an electroplex that is proposed to be formed at the sulfonium salt/polymer interfaces in the bulk. This study highlights the importance of properly selecting the counterions of the salts added in the emitting layer of PLEDs, which, in addition to their various functionalities, significantly influence device performance.</p

Determination of tetracycline and its major degradation products by liquid chromatography with fluorescence detection

A liquid chromatographic method of tetracycline and its major degradation products on a C8-reversed phase column with acidic mobile phase and fluorescence detection is described. The quantification limit, measured as the amount of sample that gave a signal ten times the peak-to-peak noise of the baseline, was: 0.25 ng for tetracycline (TC) and epitetracycline (ETC), 25 ng for and 4-epianhydrotetracycline (EATC) and 50 ng for anhydrotetracycline (ATC) of injected standard. By means of this liquid chromatography (LC) assay TC, ETC, EATC and ATC as main degradation products of tetracycline, can be separated and determined with good sensitivity and specificity within 15 min.http://www.sciencedirect.com/science/article/B6TGX-43HVHWC-1D/1/9763379e028400de01242a673bd4528