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Professor,
Materials Science and Engineering,
Indian Institute of Technology-Kanpur ,
Work Phone: (512) 2597353,
Email: saboo[at]iitk.ac.in
Materials Science and Engineering,
Indian Institute of Technology-
Email: saboo[at]iitk.ac.in
Niladri Banerjee’s Thesis
Thesis Topic:
Improved polysilane organic light emitting diodes based on poly (n-octylphenylsilane)
Improved polysilane organic light emitting diodes based on poly (n-
Polysilanes are σ conjugated polymers which shows emission in ultraviolet (UV). Due to their potential for UV emission they may be used for solid state white lighting, full color display or low cost disposable UV sensors. In spite of such potentials, their performance is affected by their stability. This occurs due to photoscission of Si-Si bonds. But all polysilanes do not degrade with the same rate and side groups play an important part in controlling the stability. They also affect the electronic structure and hence emission characteristics. In order to design efficient devices, a detailed understanding of the charge transport properties needs to be dealt with in addition to the knowledge of the role of structure in stability of the molecule. In this regard, we have investigated the effect of side organic groups on the stability of three polysilanes, namely, poly[bis(p-butylphenyl)-silane]-(PBPS)), poly(noctylphenylsilane) (PS-8) and poly[(p-n-butylphenyl)(n-octyl)silane] (P-8). Among these, PBPS and PS-8 devices had a low turn-on voltage. In this work, we have compared photoluminescence degradation and device characteristics of PBPS, PS-8 and a new polysilane, poly[(p-n-butylphenyl)(n-octyl)silane] (P-8). These three polysilanes allow us to systematically investigate the effect of the side groups attached to the Si chain. We find that the presence of alkyl chain drives the emission to deeper UV, whereas phenyl group yields a greater stability. Charge transport properties in these devices are investigated experimentally and simulation is used as a tool to understand the mechanism behind it. We found that electron mobility is much greater than hole mobility, contrary to earlier belief. We have predicted the factors limiting the device efficiency and methods to improve are examined by using Electron Transport Layers (ETL). Incorporation of ETL enhanced efficiency by almost a factor of 7. Hole blocking layer was incorporated but due to increased electron injection barrier efficiency dropped.