A Novel Approach to Anti-Soiling Coatings for Solar Modules by use of Lanthanide Oxide Films

Advances in solar module utilities underpin an important approach for novel sources of renewable energy. However, soiling remains a major obstacle when considering the use of solar modules as a sustainable replacement for electricity generation. Thus, there is an evident need for self-cleaning solar utilities. We present the design, synthesis and application of inorganic rare oxide layers (Ce₂O₃, Er₂O₃) which have been deposited by aerosol assisted chemical vapour deposition (AACVD) with intrinsic hydrophobicity. Water contact angles of up to 103 ° were established across the deposited thin films, inferring their self-cleaning potential.<br/><br/>The reduced number of examples of lanthanide oxide complexes for hydrophobic coatings using AACVD within the literature, prompted our investigation into the synthesis of volatile lanthanide β-diketonate precursors, a novel approach to self-cleaning solar modules. Notably, inorganic rare Earth oxide layers (Ce, Y, Lu, Er) have proven through various applications to be durable, UV stable, oxidant resistant and have intrinsic hydrophobicity with a water contact angle range of 110-125 °.^{1, 2} Likewise, β-diketone ligands complexes have proven to serve as effective and stable precursors. Compounds of the type [M(Y)_3,4] have been synthesised via adaption of a known synthetic route to [Ce(thd)₄] and [Er(thd)₃].^{3, 4} Where; M = lanthanide metal (Ce, Er) and Y = thd (dipivaloymethane), dbm (dibenzoylmethane).<br/><br/>AACVD of the synthesised complexes yielded lanthanide oxide films on fluorine tin doped (FTO) glass under a constant flow of nitrogen. Thermogravimetric analysis of these compounds indicated suitable deposition temperatures ranging from 400-600 °C. The most hydrophobic coatings were attained by deposition of cerium oxide onto FTO at temperatures between 400-500 °C. These rare oxide thin films were intrinsically analysed using surface analysis and characterisation techniques. Whereby X-ray photoelectron spectroscopy confirmed the presence of a mixed phase system of Ce(III) and Ce(IV) across the surface. Further analysis of the deposited thin films was conducted using SEM and XRD to determine the surface morphologies of these hydrophobic coatings.<br/><br/>References<br/><br/>1. G. Azimi, R. Dhiman, H. M. Kwon, A. T. Paxson and K. K. Varanasi, <i>Nature Materials</i>, 2013, <b>12</b>, 315-320.<br/>2. Y. Zhao, <i>Materials</i>, 2012, <b>5</b>, 1413-1438.<br/>3. M. Becht, T. Gerfin and K. H. Dahmen, <i>Chemistry of Materials</i>, 1993, <b>5</b>, 137-144.<br/>4. K. J. Eisentraut and R. E. Sievers, <i>Journal of the American Chemical Society</i>, 1965, <b>87</b>, 5254-5256.