Thermoelectric generators (TEG) are devices that can convert thermal energy in electrical power, providing a reliable and sustainable way to convert thermal waste in exploitable energy. Although, in the industrial sector a considerable amount of energy is wasted in warm run-out fluids, the lack of materials that are both abundant, environmentally friendly, with low manufacturing costs and thermoelectrically efficient, prevents the large scale usage of the thermoelectric conversion process. In this scenario, organic doped semiconductors have gained great interest, because they are non-toxic, made from abundant sources, and they can be solution processed at room temperature, at top of flexible substrates, allowing low cost fabrication of organic thermoelectric generators (OTEG).However, while p-type organic materials with good thermoelectric properties and stability are available, n-type organic materials combining good thermoelectric performances, stability and solution processability are still lacking. In this work, n-type doping of poly{(E)-2,7-bis(2-decyltetradecyl)-4-methyl-9-(5-(2-(5-methylthiophen-2-yl)vinyl)thiophen-2-yl)benzo[lmn][3,8] phenanthroline-1,3,6,8(2H,7H)-tetraone} (PNDI2OD-TVT), a donor-acceptor copolymer that has good electron transporting properties, is investigated towards the achievement of a solution processable n-type organic thermoelectric material.In particular, the doping process, using both commercial and newly synthesized benzimidazole based, solution processable dopants, has been optimized to maximize electrical conductivity in thin films. This allowed to achieve a maximum conductivity of 2.4E-2 S\cm. Such conductivity is almost four times higher than in similarly doped PNDI2OD-T2 films. Through low-temperature activation energy measurements and Seebeck coefficient measurements, the higher conductivity is attributed to an increased charge carriers bulk mobility. An optimization of the power factor led to a value of 8.7E-2 μW/mK^2, improved with respect to PNDI-T2 thanks mainly to the enhanced electrical conductivity.
In questo lavoro è investigato il processo di drogaggio in soluzione del polimero semiconduttore con struttura donore-accettore, poly{(E)-2,7-bis(2-decyltetradecyl)-4-methyl-9-(5-(2-(5-methylthiophen-2-yl)vinyl)thiophen-2-yl)benzo[lmn][3,8] phenanthroline-1,3,6,8(2H,7H)- tetraone} (PNDI2OD-TVT), derivato dal più noto poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (PNDI2OD-T2). In particolare si sono utilizzati come droganti derivati del benzimidazolo, commerciali e di ricerca, al fine di massimizzare la conducibilità elettrica del polimero. Questo materiale presenta una buona solubilità in comuni solventi organici e una superiore mobilità da effetto di campo. La massima conducibità elettrica raggiunta in film sottili di PNDI2OD-TVT drogato è di 2.4E-2 S\cm, circa quattro volte maggiore della conducibilità riportata per il PNDI2OD-T2 similarmente trattato. Tramite misure di energia di attivazione a bassa temperatura e misure di coefficiente Seebeck, l'aumento di conducibilità elettrica è correlato ad una maggiore mobilità dei portatori. Un'ottimizzazione del power factor ha portato a valori pari a 8.7E-2 μW/mK^2, confermando quindi le migliori performances del PNDI-TVT rispetto al PNDI-T2.
Enhancement of electrical conductivity through molecule doping of a polymer semiconductor for thermoelectric applications
SARTA, ELIA
2017/2018
Abstract
Thermoelectric generators (TEG) are devices that can convert thermal energy in electrical power, providing a reliable and sustainable way to convert thermal waste in exploitable energy. Although, in the industrial sector a considerable amount of energy is wasted in warm run-out fluids, the lack of materials that are both abundant, environmentally friendly, with low manufacturing costs and thermoelectrically efficient, prevents the large scale usage of the thermoelectric conversion process. In this scenario, organic doped semiconductors have gained great interest, because they are non-toxic, made from abundant sources, and they can be solution processed at room temperature, at top of flexible substrates, allowing low cost fabrication of organic thermoelectric generators (OTEG).However, while p-type organic materials with good thermoelectric properties and stability are available, n-type organic materials combining good thermoelectric performances, stability and solution processability are still lacking. In this work, n-type doping of poly{(E)-2,7-bis(2-decyltetradecyl)-4-methyl-9-(5-(2-(5-methylthiophen-2-yl)vinyl)thiophen-2-yl)benzo[lmn][3,8] phenanthroline-1,3,6,8(2H,7H)-tetraone} (PNDI2OD-TVT), a donor-acceptor copolymer that has good electron transporting properties, is investigated towards the achievement of a solution processable n-type organic thermoelectric material.In particular, the doping process, using both commercial and newly synthesized benzimidazole based, solution processable dopants, has been optimized to maximize electrical conductivity in thin films. This allowed to achieve a maximum conductivity of 2.4E-2 S\cm. Such conductivity is almost four times higher than in similarly doped PNDI2OD-T2 films. Through low-temperature activation energy measurements and Seebeck coefficient measurements, the higher conductivity is attributed to an increased charge carriers bulk mobility. An optimization of the power factor led to a value of 8.7E-2 μW/mK^2, improved with respect to PNDI-T2 thanks mainly to the enhanced electrical conductivity.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/144313