Synthesis of Conjugated Polymers and Small Molecules for Organic Light-Emitting Devices and Photodetectors
Doktorsavhandling, 2018

Production cost and environmental impact are the two major concerns that are related to the conventional optoelectronic devices. It is desirable for the modern semiconductors that they are free of toxic/costly metals, they can be processed with low-cost solution-based methods, and their optical, electronic, and mechanical properties can be easily tuned depending on the target application. In this thesis, a range of different conjugated polymers and small molecules are designed and synthesized as semiconductors for organic light-emitting diodes (OLEDs), light-emitting electrochemical cells (LECs), and organic photodetectors (OPDs).

In organic light-emitting devices, the emissive molecule is commonly mixed with a charge transporting host matrix, which can be either a small molecule or a conjugated polymer. The latter is beneficial since it does not require deposition of the emitter and matrix components in high vacuum and high temperature conditions. The polymeric materials can be dissolved and printed on a substrate of any desired size and production scale, at room temperature, and even under ambient air. The specific wavelength range of near-infrared (NIR) at λ >700 nm is of interest for a wide range of applications spanning from optical communication to biosensing. However, the low energy of NIR range poses challenges for the materials design, in terms of emission efficiency and light intensity, which are further addressed in this thesis, allowing the fabrication of high-performance NIR-OLEDs and NIR-LECs.

For photodetectors, absorption of a wide spectrum of light is beneficial in biosensing and imaging applications. Low noise and fast charge extraction are necessary for the detection of light at high speeds even at low intensities. These aspects are studied in this thesis by designing new polymers with different absorption, charge transport, and morphological properties in the photoactive layer. Two polymers enabled the fabrication of visible (red) OPDs with a low dark current (the main constituent in the noise), high detectivity, and high photoresponse speed.

solution processing

conjugated polymers



light-emitting electrochemical cell

organic photodetector

organic light-emitting diode

Vasa A-salen, Vasa Hus 2-3 entréhall, Vera Sandbergs Allé 8, Göteborg
Opponent: Prof. Andrew P. Monkman, Durham University, UK


Petri Henrik Murto

Chalmers, Kemi och kemiteknik, Tillämpad kemi

Conjugated polymers (and small molecules) are essentially like plastics. They are flexible and mechanically conformable, but unlike the common household plastics, they conduct electricity so well that they can function as semiconductors. The conventional silicon-based semiconductors are rigid, brittle, and expensive to process. In contrast, polymer-based semiconductors can be dissolved in an organic solvent to obtain a polymer ink solution. This allows the processing of the semiconductors with solution-based methods, such as inkjet printing, spray-coating, and 3D printing. Depending on the target application, the optical, electronic, and mechanical properties of the polymers can be easily tuned by making subtle changes to their chemical structure.

In this thesis, polymer-based semiconductors are designed for the attainment of emission in the special spectral range of near-infrared (NIR) region. NIR-emitting materials are used for the fabrication of high-performance light-emitting devices, which are of interest for a wide range of applications from optical communication to medical purposes. This thesis also covers the application of conjugated polymers as light-harvesting semiconductors for photodetectors. These devices convert incident light into electrical current. Photodetectors that have low noise and fast signal response allow the operation at high speeds even in low light, for example in biosensing and imaging applications.




Annan fysik

Annan kemi

Organisk kemi



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4481



Vasa A-salen, Vasa Hus 2-3 entréhall, Vera Sandbergs Allé 8, Göteborg

Opponent: Prof. Andrew P. Monkman, Durham University, UK

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