Deposition of low sheet resistance indium tin oxide directly onto functional small molecules

Abstract

We outline a methodology for depositing tin-doped indium oxide (ITO) directly onto semiconducting organic small molecule films for use as a transparent conducting oxide top-electrode. ITO films were grown using pulsed laser deposition onto copper(II)phthalocyanine (CuPc):buckminsterfullerene (C60) coated substrates. The ITO was deposited at a substrate temperature of 150°C over a wide range of background oxygen pressures (Pd) (0.67–10Pa). Deposition at 0.67≤Pd≤4.7Pa led to delamination of the organic films owing to damage induced by the high energy ablated particles, at intermediate 4.7≤Pd<6.7Pa pressures macroscopic cracking is observed in the ITO. Increasing Pd further, ≥6.7Pa, supports the deposition of continuous, polycrystalline and highly transparent ITO films without damage to the CuPc:C60. The free carrier concentration of ITO is strongly influenced by Pd; hence growth at >6.7Pa induces a significant decrease in conductivity; with a minimum sheet resistance (Rs) of 145Ω/□ achieved for 300nm thick ITO films. To reduce the Rs a multi-pressure deposition was implemented, resulting in the formation of polycrystalline, highly transparent ITO with an Rs of ~20Ω/□ whilst maintaining the inherent functionality and integrity of the small molecule substrate.