Dependence of electrical, optical, and structural properties on the thickness of IZTO thin films grown by linear facing target sputtering for organic solar cells

The dependence of electrical, optical, structural, and surface properties on the thickness of indium zinc tin oxide (IZTO) electrodes grown on glass substrates by linear facing target sputtering at room temperature was investigated. The sheet resistance of the IZTO films gradually decreased with increase in IZTO thickness, while the resistivity and transparency of the IZTO films were constant regardless of its thickness due to the complete amorphous structure of the IZTO electrodes. However, the absorption edge of the IZTO electrodes shifted to longer wavelengths with increase in thickness due to band gap narrowing caused by the effects of electron–electron and electron–impurity scattering. In addition, the performance of organic solar cells (OSCs) critically depends on the thickness of an IZTO anode electrode with different sheet resistance (Rsheet) and transparency. For a thin IZTO anode (thickness less than 440 nm), the power conversion efficiency (PCE) of the OSCs was mainly affected by the Rsheet, for a thick IZTO electrode (thickness greater than 440 nm), on the other hand, the transparency affected the PCE of the OSCs. Despite the much lower Rsheet of the 1025-nm-thick IZTO (8.86 Ω/square), the OSC showed a lower PCE (2.00%) than those with a 440-nm-thick IZTO electrode (PCE: 2.23%) due to decreased optical transparency in the wavelength region of 450–600 nm, which was the absorption region of the active materials.