Study On The Crystallinity Regulation Of Pentacene/Polymer Semiconductor Blend Film Prepared By Solution Method

Small molecular additives have been used to improve the microstructural order of solution-processed polymer films or as nucleation agents to improve film crystallization rate.However,the mechanism of action of small molecules in composite materials,dynamic behavior,microstructure morphology,and changes in material macroscopic properties are still unclear.Therefore,this topic selected Pentacene precursor small molecules,PDPP2T-TT-OD,and PBTTT-C14 as the research objects,followed prepared composite films by solution method and studied their crystallinity.It is summarized as follows:（1）Study on fabrication of polymer semiconductor/Pentacene composite films and their crystallinity.The different mass ratios PDPP2T-TT-OD/Pentacene precursor and PBTTT-C14/Pentacene precursor solutions were prepared,and then the composite film was obtained by spin coating.After that,we studied the surface morphology,crystallization behavior,and mechanism of the composite film.The results shown that high content of pentacene in composite film affect the flatness and structural uniformity of the composite film surface,resulting in a decrease in crystallinity;When the content of Pentacene was less,the structure uniformity of the composite film was better,and the crystallinity was also improved.At the same time,it was found that the polymer chains near the pentacene molecules were stacked more orderly,indicating that the pentacene molecular nucleus can induce the order of the PDPP2T-TT-OD molecules arrangement during the annealing process.In the PBTTT-C14/pentacene composite film,the interaction of the two-phase material is weak,mainly because the liquid crystal polymer had super self-assembly characteristics in the liquid crystal phase,and PBTTT-C14 will not be induced crystallization by the pentacene crystal nucleus.（2）Study on the influence of anti-solvent on the crystallinity of polymer semiconductor/Pentacene composite film.The composite film was prepared by using mixed solvents composed of different anti-solvents and polymer good solvents.Then the surface morphology and crystallization behavior of the composite film were researched.The results shown that composite films with uniform morphology can be prepared by using three groups of mixed solvents（chloroform/ethanol,chloroform/methanol,chloroform/cyclohexane）with small differences in boiling points.However,cracks appeared on the surface of composite films prepared with mixed solvents（chloroform/DMF）with large boiling points.Meanwhile,it was found that there was an optimal mixed solvent ratio（chloroform/ethanol 50:1,chloroform/methanol 20:1,chloroform/cyclohexane 20:1）,which makes the film crystallinity the highest.The surface of the PBTTT-C14/Pentacene composite film after anti-solvent treatment had massive crystal grains,which reduces the uniformity of the film.（3）Study on the relationship between the crystallinity of pentacene/polymer semiconductor composite film and the carrier transport properties.The different mass ratios pentacene/polymer semiconductor composite films and composite films with antisolvent treatment were prepared respectively,and subsequently thin film transistors were constructed.It was concluded that the highest field-effect mobility of transistors made of pure polymers was 4.06×10^-4 cm²V^-1s^-1;For the transistor prepared by the PDPP2T-TT-OD/pentacene composite film,the highest field effect mobility of the device reached 6.4×10^-3 cm²V^-1s^-1 when the mixing ratio was 15:1,which is 15times than the mobility of pure polymer-based transistors.The mobility of the transistor after ethanol antisolvent treatment was further increased to 1.11×10^-2 cm²V^-1s^-1,which is 27 times than of a pure polymer-based transistor.The improvement of carrier transport performance was attributed to the role of pentacene nucleus to induce polymer crystallization that enhancing the solid-phase arrangement of polymer molecular chains.At the same time,the addition of anti-solvent enhanced the aggregation of polymer chains in the solution,which makes the molecular chains more compactly packed in the solid-phase film,thereby facilitating charge transport.This subject studied the surface morphology and crystallization characteristics of pentacene/polymer semiconductor composite films fabricated by different mass ratios and antisolvent treatments,and also studied the influence of the parameters on the electrical properties of the composite films.It was found that pentacene nucleus can induce the orderly arrangement of PDPP2T-TT-OD molecules and significantly improve the performance of thin film transistors.At the same time,it was found that the molecular chains were more tightly packed after the anti-solvent ethanol treatment,which further improved the performance of the thin film transistor.