The Effect Of External Field On Condensed Matter Structure Of Conjugated Polymer

Conjugated polymers are widely used in organic solar cells,organic light emitting diodes and organic field-effect transistors due to their low-cost and scalability.Photovoltaic theory knowledge of conjugated polymer has been gradually improved with great value in actual application.Many researchers' goal is to increase the carrier mobility to achieve the device with high efficiency.It has been reported that improving the ordered aggregation of polymer materials and forming interpenetrating network structure can greatly improve the material carrier mobility.Polymer materials with soft material properties have a strong response to external field stimulation.Polymer performance is not only dependent on the chemical structure but also the aggregated structures.The effect of external field including solvent,concentration,spin-casting speed and electric field on condensed matter structure of conjugated polymer was mainly studied.We can control the conjugated polymer condensed matter structure through external field to improve carrier mobility and the efficiency of the photoelectric device.Polymer precursor solution could directly affect the film condensed matter structure,which will affect device performance ultimately.We systematically study the influence of solvent,concentration and speed of spin-casting on the(poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b?]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]])(PTB7)film condensed matter structure.We found that with the decrease of concentration or increase of spin-casting speed,which means decrease the entanglement of molecular chains,the conjugation length of PTB7 main chain increases,?-? interaction is enhanced,and the size of ordered aggregation increases too,because it forms ordered aggregation driven by intra-chain interaction.High entanglement degree of polymer chains which is not conducive to form ordered aggregation,forms amorphous state.Poor solvent 1,2-dichloroethane makes PTB7 main chain entangled,curly,then form amorphous state.When the solubility of solvent is reduced again,the attraction between the molecular chains is enhanced,the distance between chain segments is reduced,and ?-? interaction between a few chain segments will be enhanced.It will produce local ordered aggregation and increase the conjugate chain length.We draw the conclusion that there are mainly three kinds of state of aggregation in PTB7: first,ordered aggregation is driven by intra-chain interaction,that is to say,self-aggregation induces ordering;second,high entanglement degree of polymer chains forms amorphous state;third,when PTB7 chain entanglement density reaches a certain value,?-? interaction between a few chain segments is enhanced,which will produce local ordered aggregation.The three state of aggregation of PTB7 may exist simultaneously in the process of film forming due to the polydispersity of molecular weight and the multilayered structure of polymer.Combining with the reported literature,it is inferred that increasing the small size of aggregation formed by chain self-aggregation,and reducing amorphous state formed by the entanglement of polymer chains can improve the carrier mobility and the efficiency of the device,which has theoretical and practical significance to improve the efficiency of photoelectric device.Researches about the effect of electric field on condensed matter structure of conjugated polymer are rare,but the effect of external electric field with the direction on the conjugated polymer chain orientation can not be ignored.We studied the effect of electric field on chain orientation of different polarity of polymer through the electric field annealing above the glass transition temperature.We found that the electric field enhances ?-? interactions of poly(3-hexylthiophene)(P3HT)main chains,and increases the degree of crystallinity of P3HT;the electric field increases poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene](MEH-PPV)main chain conjugated length slightly and reduces the occurrence of aggregate formation.We draw the conclusion that P3 HT reacts obviously under the electric field due to S atom of the P3 HT main chain with strong electronegativity,big dipole moment.Although MEH-PPV contains two O atoms with strong electronegativity,they are in the symmetrical position.So MEH-PPV with small dipole moment reacts weakly under the electric field.The order degree of polar polymer is increased under the electric field.And the dipole moment(polarity)of conjugated polymery is bigger,the control of electric field is better.