Molecular Doping of Polar Conjugated Polymers
Doctoral thesis, 2019
Organic semiconductors may enable a wide range of flexible electronics, such as flexible displays or solar cells. Conjugated polymers constitute one of the most widely studied class of organic semiconductors. Molecular doping is an important tool to adjust their electrical conductivity through introduction of negative or positive charges by addition of molecular dopants. However, solution-processing of conjugated polymers with molecular dopants is limited due to precipitation and a low number of charges formed per dopant molecule as a result of dopant aggregation or inappropriate energy levels. Thus, large amounts of dopant are required that compromise the nanostructure of conjugated polymers and in turn reduce the electrical conductivity, which is furthermore sensitive to elevated temperatures or the exposure to air in case of n-doping. Therefore, ways that mitigate processing issues and increase the efficiency and stability of molecular doping are highly desired.
This thesis explores several concepts that may allow to improve the efficiency of molecular doping. A reduction of the required amount of dopant molecules is achieved by enhancing the compatibility of conjugated polymer:dopant pairs, which results in increased numbers of charges that are created per dopant molecule. In particular, polar side chains on conjugated polymers permit processing of polymer:dopant pairs from the same solution and largely suppress dopant aggregation resulting in improved electrical conductivity for p- and n-doping. Additionally, both the thermal stability of p-doped and air stability of n-doped films are found to benefit from polar side chains. Further, a low ionisation energy of conjugated polymers gives rise to dianion formation of common p-dopants. This double doping results in formation of two charges per dopant molecule and, thus, allows doubling of the doping efficiency. The concepts presented in this thesis provide several important design rules to guide the development of more efficient and stable molecularly doped conjugated polymers.
This thesis explores several concepts that may allow to improve the efficiency of molecular doping. A reduction of the required amount of dopant molecules is achieved by enhancing the compatibility of conjugated polymer:dopant pairs, which results in increased numbers of charges that are created per dopant molecule. In particular, polar side chains on conjugated polymers permit processing of polymer:dopant pairs from the same solution and largely suppress dopant aggregation resulting in improved electrical conductivity for p- and n-doping. Additionally, both the thermal stability of p-doped and air stability of n-doped films are found to benefit from polar side chains. Further, a low ionisation energy of conjugated polymers gives rise to dianion formation of common p-dopants. This double doping results in formation of two charges per dopant molecule and, thus, allows doubling of the doping efficiency. The concepts presented in this thesis provide several important design rules to guide the development of more efficient and stable molecularly doped conjugated polymers.
thermal stability
dopant dianion
air stability
compatibility
polar conjugated polymer
double doping
molecular doping
Vasa A-salen, Vera Sandbergs Alle 8
Opponent: Professor Alberto Salleo, Stanford University, USA
Author
David Kiefer
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
A Solution-Doped Polymer Semiconductor:Insulator Blend for Thermoelectrics
Advanced Science,;Vol. 4(2017)p. 1600203-
Journal article
Polar Side Chains Enhance Processability, Electrical Conductivity, and Thermal Stability of a Molecularly p-Doped Polythiophene.
Advanced Materials,;Vol. 29(2017)p. 1700930-
Journal article
Enhanced n-Doping Efficiency of a Naphthalenediimide-Based Copolymer through Polar Side Chains for Organic Thermoelectrics
ACS Energy Letters,;Vol. 3(2018)p. 278-285
Journal article
Double doping of conjugated polymers with monomer molecular dopants
Nature Materials,;Vol. 18(2019)p. 149-155
Journal article
Smarttelefoner och datorer har tagit en stor roll i vår vardag. Vi använder dem för att kommunicera med andra människor, att surfa på webben eller att streama musik eller filmer. Allt detta möjliggörs genom material med halvledande egenskaper. Deras förmåga att leda elektrisk ström ligger mellan metaller och isolatorer, som t.ex. vanlig plast. De vanligaste halvledarna som används idag har hårda och spröda egenskaper, exempelvis kisel. För att möjliggöra flexibel elektronik som t.ex. böjliga bildskärmar eller solceller behövs dock mjuka och elastiska material. Särskilda halvledande plaster som tack vare sina kemiska strukturer kan leda elektrisk ström har därför stor potential. Dessutom kan dem bearbetas genom etablerade tryckmetoder. Halvledande plaster måste ha en tillräckligt hög ledningsförmåga för att användas i modern elektronik. Detta går att uppnå med att tillsätta av laddningsbärare genom ”dopning” med speciella molekyler. Dock så försämras möjligheterna att bearbeta plasten samtidigt som man gör detta.
Denna avhandling utforskar några koncept som underlättar och effektiverar dopning av ledande plaster. Särskilda förändringar av den kemiska strukturen av halvledande plaster leder fram till en förbättrad bearbetbarhet. Dessutom undersöks en möjlighet att dubbla antalet laddningsbärare som generareas per dopningsmolekyl.
Denna avhandling utforskar några koncept som underlättar och effektiverar dopning av ledande plaster. Särskilda förändringar av den kemiska strukturen av halvledande plaster leder fram till en förbättrad bearbetbarhet. Dessutom undersöks en möjlighet att dubbla antalet laddningsbärare som generareas per dopningsmolekyl.
Smartphones and personal computers are a part of our daily life. We use them to communicate with other people, to surf on the internet or to stream music or films. All of this is made possible by materials with semiconducting properties. Their ability to conduct electricity is between those of metals and insulators, such as common polymers. The most common semiconductors today are hard and rigid materials like silicon. To realize flexible electronics, such as foldable displays or solar cells, soft and elastic materials are required. Semiconducting polymers, which due to their chemical structure can conduct electricity and can be processed with common printing techniques, have a strong potential. For the use of semiconducting polymers for modern electronics a sufficiently high electrical conductivity is needed, which can be achieved by addition of charge carriers by ‘doping’ with certain molecules. However, these dopant molecules compromise the processability of semiconducting polymers.
This thesis explores several concepts, which can help to ease doping of semiconducting plastics and increase its efficiency. Changes to the chemical structure of the semiconducting polymer lead to an improved processability with dopant molecules. Furthermore, a concept that allows doubling of the amount of charge carrier per dopant molecule is explored.
This thesis explores several concepts, which can help to ease doping of semiconducting plastics and increase its efficiency. Changes to the chemical structure of the semiconducting polymer lead to an improved processability with dopant molecules. Furthermore, a concept that allows doubling of the amount of charge carrier per dopant molecule is explored.
Subject Categories
Polymer Chemistry
Textile, Rubber and Polymeric Materials
Materials Chemistry
Areas of Advance
Materials Science
ISBN
978-91-7905-114-3
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4581
Publisher
Chalmers
Vasa A-salen, Vera Sandbergs Alle 8
Opponent: Professor Alberto Salleo, Stanford University, USA