Design, Synthesis and Characterization of Conjugated Polymers for Photovoltaics and Electrochromics
Doctoral thesis, 2018
Organic photovoltaics (OPV) have developed rapidly the last decade and is currently close to being commercially viable for niche applications. There are still some problems to overcome, however, such as device lifetimes, upscaling to large scale production and preferably a higher power conversion efficiency (PCE) as well. A major disadvantage is the use of toxic and environmentally negative solvents during processing. With the rapid rise of OPVs with polymeric donor and acceptors, so called all-polymer solar cells (all-PSC), some old assumptions about the devices are not valid anymore. Rational design of molecules can be used to achieve desired molecular properties in an attempt to overcome these problems.
To address these problems, side chain modification of conventional conjugated polymers was used to produce several series of functional polymers. A set of fluorene-based polymers with polar side chain pendant groups was used as alcohol-soluble cathode interfacial layers. This study managed to prove design principles previously used for polymer:fullerene based solar cells are still valid for all-PSCs. A separate set of polymers, based on isoindigo, included thermocleavable side chains in an effort to address the inherently unstable bulk-heterojunction structures between polymers and fullerenes. This series of polymers managed to show almost complete stabilization of the blend films upon thermal treatment.
In parallel with the developing OPV field, similar conjugated polymers have shown dramatic electrochromism, meaning they change color when an electrical field is applied over them. This peculiar property has possible uses in devices which could either switch between absorbing and transmitting such as windows or sunglasses, or switch between non-emissive coloration and transparent, useful in displays with energy consumption restrictions. The polymers used for organic electrochromics (OEC) need to show a large degree of electrochromic contrast, fast switching speeds and electrochemical stability. These two fields will be treated in this thesis with a focus on design and synthesis of functional polymers to solve the problems and material requirements for their future successful application.
polymer solar cells
all-polymer solar cells
side chain engineering
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
Synthesis and Characterization of Isoindigo-Based Polymers with Thermocleavable Side Chains
Macromolecular Chemistry and Physics,; Vol. 219(2018)
Alcohol-Soluble Conjugated Polymers as Cathode Interlayers for All-Polymer Solar Cells
ACS Applied Energy Materials,; Vol. 1(2018)p. 2176-2182
Bini, K.; Sharma, A.; Xu, X; Andersson, M. R.; Wang, E., Conjugated Polymers with Tertiary Amine Pendant Groups for Organic Electronic Applications
Bini, K.; Murto, P.; Elmas, S.; Andersson, M. R.; Wang, E., Broad Spectrum Absorption and Low-Voltage Electrochromic Operation from Indacenodithieno[3,2-b]thiophene-Based Copolymers
Bini, K.; Gedefaw, D.; Pan, C.; Bjuggren, J. M.; Elmas, S.; Sharma, A.; Wang, E.; Andersson, M. R., Orange to Green Switching Anthraquinone-Based Electrochromic Material
Jag behandlar också hur man kan använda halvledande polymerer som byter färg när man leder en elektrisk spänning över det. Genom att designa molekylerna medvetet kan man påverka deras egenskaper för att visa olika färger både före och efter de utsätts för ett elektriskt fält. Denna dramatiska egenskap kan användas för flexibla fönster som kan förmörkas med ett knapptryck, solglasögon som automatiskt blir mörkare om solen är extra ljus. De kan också användas som en färgad komponent i en skärm med e-bläck som ger en behaglig läsupplevelse för en bråkdel av batteriförbrukningen jämfört med en vanlig skärm.
I have also treated how to use semiconducting polymers that switch colors when exposed to an electric field. By designing the molecules rationally it is possible to affect their properties to give different colors before and after exposure to an electrical field. This dramatic property can be used for flexible windows that can be darkened with a push of a button, sunglasses which automatically darken when the sun is extra bright. They can also be used as a colored component in a screen of e-ink, which gives a pleasant reading experience for a fraction of the battery consumption when compared to ordinary screens.
Textile, Rubber and Polymeric Materials
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4515
Opponent: Wouter Maes, Hasselt University, Belgium