Thin film devices precursor polymer

Electropolymerization represents a useful method to control precisely the deposition of thin films of conducting polymers. These thin films have a wide variety of applications in optical devices [29]. Walder and coworkers showed that photocurrents could be generated using a trilayer thin film. The three different electropolymerized polymers were cleverly prepared from a common precursor, 4-methyl-4 -(2-pyrrolyl-1 -ethyl)-2,2 -bipyridine 7 two were alkylated, diquat derivatives and one was the Ru metal complex of this ligand, which acted as a sensitizer. The appropriate ordering of the triad in terms of their redox potentials led to the maximizing of the photocurrent (Scheme 7.2) [30],... 

This polymerization strategy is extensively used for the synthesis of PPV and its substituted derivatives. Wessling and Zimmerman [38] developed a method for the synthesis of PPV via thermo-conversion of sulfonium intermediate (prepolymer) into PPV to yield its film. In the Wessling precursor route l,4-xylylene-bis-(dialkyl sulfonium)-dichloride is used which upon elimination of tetrahydrothiophene and HCl yields PPV polymer. Fig. 5. The thermo-conversion mechanism yields pin-hole free thin films of conjugated polymers applicable for PLED fabrication. The thermo-conversion temperatures can be lowered to as low as 100 °C using bromide derivatives which can help in the fabrication of flexible PLED devices. 

Conversion of the sulfonium precursor polymer 10 to PPV 1 is typically achieved by heating thin films to as high as 300 °C in high vacuum (10 mbar) for a period of several hours.The elimination conditions have a substantial influence on the properties of the thin film material particularly in device applications. Studies on the elimination process have shown a complex multistep mechanism but it is instructive to remember that the elimination products from a sulfonium chloride precursor polymer are HCl and thioethers. The size of the sulfonium group has been shown to influence both the intrachain and... 

The first decision in choosing a synthetic method for a PPV material is the way in which the material will be processed (Scheme 7.8). The precursor routes will enable the preparation of solvent-resistant and more durable thin films of PPV. This is particularly desirable if a multilayer device structure is required for the application. When choosing different precursor methods, it is important to assess the criteria of the application. Most precursor methods involve a thermal elimination step to convert the precursor polymer to the PPV material. Sul-fonium precursors require higher-temperature elimination compared to sulfinyl precursors. This makes the sulfinyl route compatible with deposition on plastic substrates. Another factor to consider in precursor methods is the nature of the elimination byproducts. Sulfonium precursors convert to PPV with elimination of acids, such as HCl or HBr, which has been shown to be detrimental to device performance. Xanthate and dithiocarbamate routes involve the elimination of amine and CO2 and CS2, respectively. 

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