Dependence of indium–tin–oxide work function on surface cleaning method as studied by ultraviolet and x-ray photoemission spectroscopies

Abstract

The effect of the method used to clean indium–tin–oxide (ITO) on its work function was investigated by ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy. With only ultrasonic cleaning in the organic solvent, considerable carbon contamination remained on the ITO surface and the work function was low (4.5 eV). In contrast, ultraviolet (UV)–ozone treatment removed significant carbon contamination, with an increase in the work function to 4.75 eV, which improves the hole-injection efficiency into the organic hole-transport layer in organic electroluminescent devices. Although carbon contamination on the ITO surface was also removed by Ar+ sputtering, it was accompanied by the removal of oxygen from ITO, and the work function was reduced (4.3 eV). Three factors, i.e.,: (i) C-containing contaminants, (ii) the O/In ratio, and (iii) the In/Sn ratio on the ITO surface affect the work function. The present results and those of other workers suggest that these three factors affect the work function in the order: (ii)>(i)>(iii), and (i) is the main cause of the increase in the work function in the UV–ozone or O2 plasma treatments.

Efficient hole-blocking layer-free planar halide perovskite thin-film solar cells

“…The improved coverage should reduce the amount of direct contact between the FTO and the HTL, which should result in increased R sh and carrier lifetime, and therefore V OC . Furthermore, UVO treatment has also been widely reported to increase the work functions of metal oxides [28][29][30][31] . It is possibly through the reduction of the concentration of oxygen ARTICLE vacancy and therefore a downshift of Fermi level 31 .…”

Mechanism for resistive switching in chalcogenide-based electrochemical metallization memory cells

“…Herein, the SB height of ZnS/ITO is estimated from the difference between the electron affinity of ZnS and the work function of ITO (∼4.3 eV for ITO cleaned by Ar ion sputtering). 50 The impedance is determined by the ZnS/ITO SB at a positive bias; while at a negative bias, the impedance is determined by the Cu/ZnS SB. The different SB heights result in a rectifying I-V curve with a higher current value in the positive voltage branch, as shown in Fig.…”

Storage of an electric field for photocurrent generation in ferroelectric-functionalized organic devices

“…Substrates were pretreated by sequential ultrasonication with 2-propanol, acetone and chloroform for 15 min each. In addition to the ultrasonication, the patterned ITO substrates were then treated with ultraviolet-ozone for 2 min, which is known to raise its work function 42 . After the deposition of the CuPc films at a pressure of 5 Â 10 À 4 Pa with a rate of 0.05 nm s À 1 by using vacuum vapour deposition, the P(VDF-TrFE) layers were fabricated via spin coating from 40 mg ml À 1 (for thick films) and 2 mg ml À 1 (for the ultrathin films) dimethylformamide (DMF) solutions.…”