Optical constants and electrical conductivity of polysilanes: Effects of substituents and iodine doping

Abstract

This work deals with the effect of chemical structure and iodine doping on electro-optical characteristics of different polysilanes in the solid state. The properties of polymethylphenylsilane homopolymer were compared with those of polysilane copolymers containing diphenylsilylene structural units associated with either methylhydrogen- or methylphenylsilylene moieties. Their optical parameters, such as Urbach energy and optical band gap, were evaluated using the method proposed by Tauc. The forbidden gap values for the studied polysilanes are reduced after doping from 3.22–3.46 eV to 2.47–2.64 eV, while the electrical conductivities were found in the range of 6.2 10⁻¹¹ – 1.2 10⁻⁸ S/cm for pristine samples, and increased by 2–3 orders of magnitude following their doping, depending on the nature/content of the organic substituents attached to the silicon main chain. A simple mathematical approach starting from Tauc classical theory was used to establish allowed direct optical transitions for both undoped and doped polysilane samples. The obtained data indicated that the polysilane films with a high content of phenyl side groups presented the best properties for their use in electro-optical applications.

Graphical Abstract

Keywords:

• Polysilane
• iodine doping
• optical properties
• conductivity

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by a grant of the Romanian Ministry of Research and Innovation, CCCDI-UEFISCDI, project number PN-III-P1-1.2-PCCDI-2017-0194, contract number 25PCCDI/2018, within PNCDI III.