Efficient and controllable vapor to solid doping of the polythiophene P3HT by low temperature vapor phase infiltration

Efficient doping of organic semiconductors is an important prerequisite for the fabrication of high performance organic electronic devices. In this work, we describe a novel single precursor low-temperature (70 °C) vapor phase infiltration (VPI) process to dope poly(3-hexyl)thiophene (P3HT). The infiltration is performed with the metal containing atomic layer deposition (ALD) precursor MoCl₅. The conductivities of the polymer are assessed with four-point probe measurements and showed significant enhancement by up to 5 orders of magnitude, confirming the efficiency of the VPI process. The chemical changes resulting from the infiltration of P3HT are characterized by applying UV-Vis-NIR, Raman spectroscopy, and FTIR. The crystalline state of the material is analyzed by X-ray diffraction (XRD). SEM micrographs and AFM images show that the morphologies of the samples before and after the MoCl₅ infiltration process do not seriously change. TEM images of cross-sections of the thin film clearly show that the vapor phase infiltration process results in the incorporation of Mo into the bulk of the polymer.