Design, Synthesis and Characterization of Conjugated Polymers for Photovoltaics and Electrochromics
Doctoral thesis, 2018

With the invention of organic electronics, a new class of materials needed to be explored and suitable applications found. The use as semiconductors in many different devices has been explored, where photovoltaics, light-emitting diodes and field-effect transistors have been prominent. For most applications the organic semiconductors have some advantages when compared to their inorganic counterpart, such as molecular design variability, solution processing and flexible mechanical properties. These advantages are quickly making organic semiconductors an interesting alternative in a wide variety of fields.

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.

organic electronics

conjugated polymers

electrochromic polymers

polymer solar cells

all-polymer solar cells

side chain engineering

Opponent: Wouter Maes, Hasselt University, Belgium


Kim Bini

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)

Journal article

Alcohol-Soluble Conjugated Polymers as Cathode Interlayers for All-Polymer Solar Cells

ACS Applied Energy Materials,; Vol. 1(2018)p. 2176-2182

Journal article

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

Organisk elektronik är ett revolutionerande fält. Med hjälp av halvledande polymerer kan mycket av vår moderna elektronik ersättas av billiga, flexibla och lättviktiga alternativ. I denna avhandling behandlar jag hur halvledande polymerer kan användas för att producera solceller som skulle kunna ersätta en stor del av den moderna elektricitetsproduktionen. Det beror på polymerernas förmåga att lösas upp i lösningsmedel och bilda ett bläck, för att sedan kunna tryckas med tryckpressar – som en nyhetstidning! På så vis kommer storskalig produktion bli både snabb och billig. Detta kommer vara en viktig del i den nödvändiga omställningen av vår energiproduktion från fossilbränsle till förnyelsebart. För att göra en grön teknik grönare har jag forskat på hur man kan designa halvledande polymerer i gröna lösningsmedel och göra dem hållbarare på lång sikt och även hur man kan använda dem på ytskiktet av en elektrod för att förbättra solcellseffektiviteten.

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.

Organic electronics is a revolutionary field. With the use of semiconducting polymers much of our modern electronics can be replaced by cheap, flexible and light alternatives. In this thesis, I treat how these semiconducting polymers can be used to produce solar cells which could replace a large part of the modern electricity production. This depends on the polymers’ ability to be dissolved and form an ink, which can be printed with large roll-to-roll printers – like a newspaper! That way large scale production can be both fast and cheap. This will be an important piece in the necessary restructuring of the energy production from fossil fuels to renewables. To make a green technology greener, I have researched ways to design semiconducting polymers soluble in green solvents and making them more durable for long term use and also how to use them on the interface of electrodes to improve solar cell efficiency.

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.

Subject Categories

Polymer Chemistry

Polymer Technologies

Textile, Rubber and Polymeric Materials



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4515




Opponent: Wouter Maes, Hasselt University, Belgium

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