Surface tailoring of newly developed amorphous Zn-Si-O thin films as electron injection/transport layer by plasma treatment: Application to inverted OLEDs and hybrid solar cells

摘要

Graphical abstractDisplay OmittedHighlights•Influence of oxygen/argon plasma treatment to the energy level of ZnSiO/organic material is studied by in-situ UPS.•The work function of air exposed ZnSiO is easily recovered to its intrinsic value of 3.5eV by Ar-plasma treatment.•High exciton–dissociation efficiency for hybrid organic solar cell is attained by forming strong dipole on the surface of ZnSiO.AbstractWe report a unique amorphous oxide semiconductor ZnSiO (a-ZSO) which has a small work function of 3.4 eV for as-deposited films. The surface modification of a-ZSO thin films by plasma treatments is examined to apply it to the electron injection/transport layer of organic devices. It turns out that the energy alignment and exciton dissociation efficiency at a-ZSO/organic semiconductor interface significantly changes by choosing different gas (oxygen or argon) for plasma treatments (after a-ZSO was exposed to atmospheric environment for 5 days). In situ ultraviolet photoelectron spectroscopy (UPS) measurement reveals that the work function of a-ZSO is increased to 4.0 eV after an O2-plasma treatment, while the work function of 3.5 eV is recovered after an Ar-plasma treatment which indicates this treatment is effective for surface cleaning. To study the effects of surface treatments to device performance, OLEDs and hybrid polymer solar cells with O2-plasma or Ar-plasma treated a-ZSO are compared. Effects of these surface treatments on performance of inverted OLEDs and hybrid polymer solar cells are examined. Ar-plasma treated a-ZSO works well as the electron injection layer in inverted OLEDs (Alq3/a-ZSO) because the injection barrier is small (∼ 0.1 eV). On the other hands, O2-plasma treated a-ZSO is more suitable for application to hybrid solar cells which is benefiting from higher exciton dissociation efficiency at polymer (P3HT)/ZSO interface.