Structural, Optical, and Electronic Properties of Self-Assembled Di-(3-diaminopropyl)-viologen on Indium Tin Oxide Electrode Surfaces

Abstract

Di-(3-aminopropyl)-viologen (DAPV) on indium tin oxide (ITO) films were prepared as self-assembled monolayers (SAMs), and were well characterized using scanning tunneling microscopy (STM), UV−vis absorption spectroscopy, and electrochemistry. Furthermore, DAPV on ITO SAMs film was applied to a photoinduced charge transfer system. The STM images of the ordered SAMs on ITO showed round-shaped small domains with an average size of 15 nm, and the periodicity of the molecular rows in the domains was approximately 2.1 ± 0.2 nm. The energy band gap, the highest occupied molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO) of DAPV on ITO were measured using a UV−vis absorption spectrum and a cyclic voltammogram. The energy band gap, HOMO, and LUMO of DAPV on ITO were 1.6, −5.7, and −4.1 eV, respectively. Under illumination, the DAPV on ITO films showed a current change of 28 nA/cm2 under an air mass (AM) 1.5 condition (I = 89 mW/cm2) in a vacuum (10−6 torr). Furthermore, SAM films on ITO showed a photocurrent of 52.5 μA/cm2 under an AM 1.5 condition (λ = 530 nm, 3.3 mW/cm2) in the presence of I−/I3−/CH3CN.