In English

Electron microscopy and spectroscopy of all-polymer solar cell active films

lisa toller
Göteborg : Chalmers tekniska högskola, 2014. 65 s.
[Examensarbete på avancerad nivå]

This work concerns the microstructure of all-polymer solar cell active films, where the active film of an all-polymer solar cell is the photoactive polymer layer used to harvest light. The morphology of the active film is important for the efficiency of the solar cells. Both charge separation, facilitated by smaller domains with more interfaces, and charge carrier mobility, improved by crystalline domains in the material, are of importance. The films in this work consist of the two polymers TQ1 and N2200. Active films spin coated from different solvents are compared as well as films with or without thermal annealing. The active films containing both polymers in a bulk heterojunction are also compared to films of a single polymer spin coated from the same solvents. The films were studied by transmission electron microscopy using bright field imaging and electron diffraction. Scanning electron microscopy and atomic force microscopy were also used to image the surface structure of the films. It was found that films of pure N2200 spin coated using ortho-dichlorobenzene or chloroform were crystalline as evidenced by electron diffraction. The films spin coated with ortho-dichlorobenzene showed a fibrillar structure on the surface. This was in agreement with what was previously known about solution processed films of N2200. For the bulk heterojunctions it was found that films spin coated with chloroform crystallised during thermal annealing whereas thermal annealing did not seem to affect the films spin coated with ortho-dichlorobenzene which showed crystalline order in both as-spun and annealed films. The data from the bulk heterojunctions showed that the morphology of the films spin coated with chloroform had features on a smaller length scale when compared to films spin coated with ortho-dichlorobenzene. This will affect the power conversion efficiency of devices made of these films, as both features on a smaller length scale and crystalline domains are favourable.

Nyckelord: All-polymer solar cells, TQ1, N2200, bulk heterojunction, spin coating,

Publikationen registrerades 2015-01-02. Den ändrades senast 2015-01-14

CPL ID: 209399

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