Study On New Organic Pyroelectric Materials Based On DAST

Since the 20th century,thermoelectric effects and their applications have been widely and deeply investigated.Many excellent thermoelectric materials have been discovered and widely applied in energy harvesting,dye degradation,infrared detection,and etc.With the development of convenient wearable devices,the performance,price,weight,wearability,and convenience of the thermoelectric related devices are highly required.Although organic thermoelectric devices can meet these requirements,their thermoelectric coefficients are generally one order of magnitude lower than those of inorganic thermoelectric materials,resulting in low output signal of the organic thermoelectric devices,and limiting further applications of the organic thermoelectric materials.To this end,new organic thermoelectric materials with excellent thermoelectric performance were explored in this thesis,which results will promote further development of organic thermoelectric devices.The main results of this work include:（1）In this work,high-quality 4-（4-dimethylaminostyryl）methylpyridine p-methylbenzene sulfonate（DAST）single crystals were successfully grown by the combination of the tilted plate method and slow growth method.The electric hysteresis loop,relative dielectric constant,loss factor,and pyroelectric coefficient of the as-grown DAST single crystal were measured.The results revealed that under an electric field of150 KV/cm,the residual polarization strength（P_r）of the DAST single crystal was 1.7μC/cm²,and the saturation polarization strength(P_max)was 3.6μC/cm².The pyroelectric coefficient of DAST single crystal was experimentally measured to be 37.5μC/m²·K,which is higher than that（27μC/m²·K）of the commercial organic PVDF,and even comparable to those of inorganic materials such as lithium niobate（Li Nb O₃）（40μC/m²·K）.In addition,the relative dielectric constant of the DAST single crystal was 4.2,and the loss factor was 0.012.These results indicated that DAST is a new organic pyroelectric material with excellent properties that has never been reported.（2）DAST thin films were prepared by spray coating,and the effects of the annealing temperature on the morphology,crystallinity,and pyroelectric properties of the resulting films were investigated.The ferroelectricity,specific heat capacity,relative dielectric constant,loss factor,and pyroelectric coefficient of the as-prepared films were also measured,by which the figure of merit for the DAST thin films was deduced.The results showed that annealing at high temperature（160 ℃）leads to the increase of the crystallinity,ferroelectricity,and pyroelectric coefficient（33.18μC/m²·K）of the DAST thin films.Based on the measured relative dielectric constant（8.5）,loss factor（0.012）,and specific heat capacity（1.7 J/g·°C）of the DAST thin films at room temperature,the FOM values for current response（F_i）,voltage response（F_v）,and detectivity（F_D）were estimated to be 2.7×10^-9 C·cm/J,3.6×10^-11 C·cm/J,and 2.8×10^-9 C·cm/J,respectively.（3）DAST-PVDF composite films were prepared by solution casting,and the effects of the DAST concentration,annealing temperature,polarization temperature,and polarization voltage on the pyroelectric coefficient of the composite films were investigated.The results revealed that the pyroelectric coefficient of the DAST-PVDF composite films was 35.42μC/m²·K when the DAST concentration was 8 wt%,the annealing temperature was 100°C,the polarization temperature was 110°C,and the polarization voltage was 600 V.