SOLUTION-PROCESSABLE, LOW WORK FUNCTION N-DOPED ORGANIC SEMICONDUCTORS

Abstract

Electrodes with low work functions (WF) are required to efficiently inject electrons into semiconductor devices. However, when the work function drops below about 4 eV, the electrode suffers oxidation in air, which prevents its fabrication in ambient conditions. In this thesis, I describe ambient stable and solution processable polycationic electron injection layers (EILs) with multivalent counteranions, which can act as powerful latent electron donors when dispersed as small ion clusters in a matrix to achieve EIL WF as low as 2.4 eV. The anions can n-dope semiconductor cores of low electron affinities via ground state mechanism in vacuum, photosensitization by exposure to ultraviolet light or hole-sensitization upon bias application in devices. The EIL performances are studied as the following are varied: the chemical structures of the polymeric semiconductors, the counteranion species and composition, as well as the spacer chain lengths and tethered cations of the side chains.