Silicon phthalocyanines as N-type semiconductors in organic thin film transistors

Abstract

Silicon phthalocyanines (SiPcs) represent a large class of molecules that have been studied as donors, acceptors and ternary additives in organic photovoltaics but not in organic thin-film transistors (OTFTs). We synthesized three novel SiPcs using axial substitution and examined their performance as the active layer in bottom-gate bottom-contact (BGBC) OTFTs. All three molecules exhibit N-type behaviour, with the dibenzoate substituted SiPc showing the greatest field-effect mobility of roughly 6 × 10⁻⁴ cm² V⁻¹ s⁻¹ in vacuum. This performance improved to >0.01 cm² V⁻¹ s⁻¹ when using a combination of dielectric modification with octadecyltrichlorosilane (ODTS) and a substrate temperature during deposition of 200 °C. These promising results point towards the possibility of high performance N-type SiPcs by exploring the wealth of available options in axial and peripheral substitution and careful process control during fabrication.