Effect of dendrimer underlayers on microstructure, morphology, optical, and electrical properties of direct current sputtered indium tin oxide thin film

Minimization of surface roughness is extremely important for sputtered indium-tin oxide (ITO) films used for electrodes in solar cells, organic light-emitting diodes (OLED), and other device applications. One of the techniques used to achieve smooth ITO films is the optimization of process parameters, together with the injection of cesium vapor into the plasma. We have investigated an alternative, more straightforward approach, the application of dendrimer monolayers by dip- or spin-coating techniques before ITO sputter deposition at ambient temperatures. The ITO films have been characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM), and their microstructure and morphology have been correlated with optical and electronic properties, including transmission and resistivity. The presence of the dendrimer underlayer appears to mediate the film's roughness by reducing grain size and improving adhesion. The most significant effect is seen in films sputtered at low powers. This is expected, as a high level of ion bombardment is likely to damage or destroy the dendrimer underlayer. The observed improvement is most encouraging for electrodes in solar cells and flexible display applications, where low resistivity and low surface roughness are required at low deposition power at room temperature.