Charge Transport across Phosphonate Monolayers on Indium Tin Oxide†

Transition voltage spectroscopy was used to measure the charge injection properties of monolayers of bithiophene phosphonate, quarterthiophene phosphonate, and decylphosphonate covalently bonded to an indium tin oxide surface. Hysteresis was observed for all three phosphonates, which is possibly explained by charge retention at the phosphonate−ITO interface. Unlike previous work on thiolate-based molecular junctions, there is no significant difference between the charge injection barriers of the three phosphonates, suggesting that the phosphonate moiety dominates the observed charge injection properties.