Synthesis and properties of pi-conjugated polymers for organic photovoltaics
Doctoral thesis, 2013

Organic photovoltaics is a renewable energy technology able to solve global warming and the upcoming energy gap, issues that both originate from fossil fuel consumption. Out of all renewable energy sources, the Sun is the only source that produces enough energy to fulfill all our energy needs, now and in the future. Photovoltaics based on -conjugated polymers are envisioned to offer a low cost alternative to the present technology, but optimization of the polymer structure is needed to achieve efficiencies high enough to make this technology economically viable. This thesis deals with both the optimization of several parent structures via the process of energy level engineering and establishing structure-property relationships upon alteration of these parent structures. The initial work explored the effect of carbon-silicon exchange on various physical, optical and photovoltaic properties of fluorene/silafluorene-based copolymers. The optical, redox and photovoltaic properties of these polymers remained virtually unchanged except for the thermal behavior. The work was continued by optimizing the energy levels and bandgap of TQ1 with the aim to surpass its already high power conversion efficiency of 6%. Aside from improved spectral coverage and energy level optimization, several interesting structure-property relationships were found. Finally, another well-performing structure, PDPPTPT, was modified with alkoxy sidechains to investigate the effect on various polymer properties. Aside from a redshifted absorption, additional flexibility in the polymer backbone was obtained with concomitant changes in polymer properties. By comparing polymer and oligomer properties, methoxy substitution seems to initially increase melting and crystallization temperatures, but this is then supposedly counteracted due to increased irregularity in the polymer backbone.

organic photovoltaics

structure-property relationships

Conjugated polymers

energy level engineering

Opponent: Prof. René A. J. Janssen


Renee Kroon

Chalmers, Chemical and Biological Engineering, Polymer Technology

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Mängden av fossila bränslen är begränsad och inom en nära framtid kommer det bli en bristvara och de fossila bränslena kommer därmed inte kunna användas som en källa för energi. Förbränningen av fossila bränslen bidrar dessutom till den globala uppvärmningen och därför behövs det hållbara energikällor som dessutom kan återbildas, förnybar energi.Solen är den största källan och producerar hela vårt årsbehov av energi, under endast en timme! Solceller tar solljuset och omvandlar det till elektricitet. Även om dagens solceller är effektiva och driftsäkra är de fortfarande för dyra för att kunna konkurera med energin som kommer från fossila bränslen. På 90-talet upptäckte man att polymerer, så kallade konjugerade polymerer, kan användas för detta ändamål. Blandar man dessa konjugerade polymerer med ytterligare en nyligen upptäckt molekyl, Buckminster fullerenen, kan man omvandla solljuset till elektricitet. Genom att använda en kostnadseffektiv produktionsprocess kan effektiva och billiga polymera solceller tillverkas.Designen av dessa konjugerade polymerer är mycket specifik och utbytet av en atom mot en annan kan redan omvandla en dåligt fungerande polymer till en bra fungerande. Denna avhandling behandlar designen, syntesen och utvärderingen av konjugerade polymerer. Syftet är att etablera viktiga förhållanden mellan struktur och egenskap med slutmålet att förstå hur effektivitet, kostnad och livstid kan kombineras till nästa generations energi källa.

The amount of fossil fuels on Earth is limited, so the consumption of fossil fuels leads to a shortage of fossil fuels and therefore a shortage of energy in the near future. Also, burning fossil fuels for energy production contributes to global warming. Therefore we need to use clean energy sources that replenish themselves: renewable energy. The Sun is the largest renewable energy source we can use. It produces all the energy we yearly need, in only 1 hour! Solar cells are able to harvest sunlight and convert it into electricity. Even though the current solar cells are efficient and reliable, they are still too expensive to compete with the energy produced from fossil fuels. In the 90’s it was discovered that specially designed plastics, called ‘conjugated polymers’, can be used for this purpose. By mixing these conjugated polymers with another recent discovery, the ‘buckyball’, sunlight can be converted into electricity. Combined with a very cheap production process, polymer solar cells hold the promise to be efficient and cheap. The design of these conjugated polymers is very specific since changing one atom most of the time changes a bad performing polymer in a well performing polymer, or vice versa. This thesis deals with the design, synthesis and analysis of conjugated polymers to establish these structure-property relationships with the ultimate goal to understand how efficiency, cost and lifetime can be combined into a next-generation energy source.

Subject Categories

Polymer Chemistry

Organic Chemistry

Driving Forces

Sustainable development

Areas of Advance

Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)


Materials Science




Opponent: Prof. René A. J. Janssen

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