SnO2 Films Elaborated by Radio Frequency Magnetron Sputtering as Potential Transparent Conducting Oxides Alternative for Organic Solar Cells

Abstract

Transparent conducting oxides (TCOs) are a crucial component of solar cells. Tin-doped indium oxide (ITO) is the most employed TCO, but the scarcity and high price of indium induce a search for lower-cost TCOs with equivalent properties as substitutes. Tin dioxide (SnO₂) films have many advantages, such as rich sources of material, low prices, and nontoxicity. SnO₂ films present a high visible-light transmittance, near-infrared light reflectivity, and excellent electrical properties. They also have a higher chemical and mechanical stability compared to ITO. The aim of this work is to elaborate SnO₂ films by radio frequency (RF)-magnetron sputtering in order to use them as electrodes for organic solar cells (OSCs). The SnO₂ films were deposited on glass, SiO₂, and quartz substrates in a mixed environment of Ar and O₂. X-ray diffraction (XRD) measurements show that the as-deposited SnO₂ films are polycrystalline with a cassiterite tetragonal structure. Scanning electron microscopy (SEM) analysis showed that the films are homogeneous, continuous, and nanostructured. The electrical resistivity and average optical transmittance of the samples are about 10^–3 Ω.cm and over 80%, respectively. The estimated optical band gap (E_g) is around 4.0 eV, while the work function (WF) of the films is around 5.0 eV. The SnO₂ films are used as electrodes for inverted OSCs, using poly(3-hexylthiophene-2,5-diyl): [6,6]-phenyl-C60-butryric acid methyl ester (P3HT:PC₆₀BM) as the active layer. The device’s open-circuit voltage (V_OC) and short-circuit current density (J_SC) are similar to those obtained for the inverted OSCs employing ITO as the same electrode. Even if the achieved power conversion efficiency (PCE) is lower compared to the value for the reference OSC with an ITO electrode, these results are promising and place SnO₂ TCO as a potential candidate to replace ITO.