Effects of oxygen plasma treatments on the work function of indium tin oxide studied by in-situ photoelectron spectroscopy

Modifying the Surface Properties of Indium Tin Oxide with Alcohol-Based Monolayers for Use in Organic Electronics

“…The work function of ITO electrodes at the interface with potential HTLs can be adjusted using SAMs. − ,,,, Monolayers can be used to effectively tune the work function of metals and semiconductors, while increasing the efficiency of the hole injection process. ,, These achievements result from the creation of a new permanently induced surface dipole within the monolayers. UPS measurements can be used to determine the work function of a material. ,, Previous UPS studies compared the work functions of monolayers of n -alkylphosphonic acid and other phosphonic acids on ITO to those of Triton X-100 cleaned ITO and oxygen plasma treated ITO. ,, The Triton X-100 cleaned ITO had a work function of 4.6 eV, and that for the oxygen plasma treated ITO was 5.1 eV. , The n -alkylphosphonic acid monolayers decreased the work function of ITO by 0.6 eV in comparison to the oxygen plasma treated ITO. Other phosphonic acids, such as fluorinated and phenylated species, either had not affected or increased the work function of the plasma treated substrates.…”

“…Ultraviolet photoelectron spectroscopy (UPS) measurements can be used to determine the work function of a material. 19,[48][49] Previous UPS studies compared the work functions of monolayers of n-alkylphosphonic acid and other phosphonic acids on ITO to those of Triton™ X-100 cleaned ITO and oxygen plasma treated ITO. [3][4]36 The Triton™ X-100 cleaned ITO had a work function of 4.6 eV, and that for the oxygen plasma treated ITO was 5.1 eV.…”

“…[4][5][6][15][16][17] With the clean native ITO, high work functions are achieved through the polar oxo and hydroxyl surface functional groups, which are often created through specific treatments that include oxygen plasma, ultraviolet (UV)-ozone, or Radio Corporation of America standard cleaning procedures (e.g., RCA-1). 4,[18][19] These surface functional groups are, however, not well suited for direct contact with the HTL found in many organic based electronics because the polar groups of the native ITO surfaces exhibit an incompatibility due to their high surface energy. 2,4,8 These surfaces also undergo rapid changes-including loss of surface hydroxyls and polar oxo groups-under ambient conditions, which results in a decrease in the work function.…”

“…This mismatch in work functions, called the hole injection barrier, is directly associated with the efficiency of devices incorporating HTLs and ITO. Work functions of clean native ITO can vary from 4.2 to 5.1 eV, depending on the procedures used to clean the surfaces and prepare the ITO films. − ,− With the clean native ITO, high work functions are achieved through the polar oxo and hydroxyl surface functional groups, which are often created through specific treatments that include oxygen plasma, ultraviolet (UV) ozone, or Radio Corporation of America standard cleaning procedures (e.g., RCA-1). ,, These surface functional groups are, however, not well-suited for direct contact with the HTL found in many organic-based electronics, because the polar groups of the native ITO surfaces exhibit an incompatibility due to their high surface energy. ,, These surfaces also undergo rapid changesincluding loss of surface hydroxyls and polar oxo groupsunder ambient conditions, which results in a decrease in the work function . This incompatibility at the interface between the ITO and the HTL leads to a nonuniform wetting of the organic films, and subsequent changes to the interface can lead to delamination of the HTL.…”

The Impact of the Surface Modification on Tin-Doped Indium Oxide Nanocomposite Properties

“…Removing carbon contamination by cleaning the surface using oxygen plasma increases the work function significantly according to UPS measurements. Based on XPS results, using the plasma induces a dipole layer on the surface of the ITO, which leads to increasing the work function of the ITO [ 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 ].…”