Nano-engineered solution processed solid-state semiconductor lasers

Abstract

This thesis describes various methods for patterning the electronic and physical structure of conjugated polymers, ranging from molecular to sub-wavelength scales. This was done to improve the operation, fabrication and application of conjugated polymer distributed feedback lasers and additionally new gain materials were explored to overcome to some of the limitations. Organic lasers are currently limited to pulsed operation and unable to achieve continuous wave operation. The effects of triplet states preventing continuous wave operation is explored here, and a triplet management scheme based on selectively quenching guest molecules was used to structure the excited states. Using excited state spectroscopy this scheme was optimised and then utilised to extend the conjugated polymer lifetime by a factor of ~3. CH₃NH₃PbI₃ perovskite waveguides were also fabricated and then nanostructured using nanoimprinted substrates to make one of the first perovskite distributed feedback lasers. Perovskite semiconductors share many of the same properties as organic semiconductors with the potential not to suffer from triplet-state interactions. The physical engineering of conjugated polymers was also explored with the development of a new solvent based nanoimprinting method for the nano-structuring of polymer films. This processed allowed for the imprinting of sub-wavelength scale gratings directly into conjugated polymers. The structured polymer films were subsequently explored as data transmitters as well as distributed feedback lasers. Lastly, the engineering moved to the molecular scale. Using cocaine molecules, a specially synthesised molecularly imprinted polymer used to develop the first “laser turn-on” detection system, combing both physical and electronic structuring themes of the thesis.