Heteroepitaxial and homoepitaxial nucleation strategies to grow Sb2S3 nanorod arrays and therefrom a derived gain of 7.18%-efficient Sb2(S,Se)3 quasi-nanoarray heterojunction solar cells

Narrow-bandgap semiconductor nanoarrays are the promising photon-harvesters for photovoltaics because of their unique optoelectronic properties. To prepare the solution-processed nanoarrays of antimony sulfide (Sb2S3) and antimony selenosulfide (Sb2(S,Se)3) that are of a great potential in photovoltaics are still challenging. Here, a tiny-Sb2Se3-seed assisted solution-processing method for growing Sb2S3 nanorod array (NA) on non-epitaxial-for-seed-growth substrates is developed for the first time, complementing the tiny-Sb2S3-seed-derived Sb2S3-NA growth on TiO2 nanoparticle film that is actually epitaxial for the Sb2S3 seed growth. The orientation-competing-epitaxial nucleation/growth mechanisms based on the heteroepitaxial and homoepitaxial nucleation effects of randomly formed tiny seeds are proposed for, respectively, understanding the tiny-Sb2Se3-seed-derived Sb2S3-NA growth and the unavailable tiny-Sb2S3-seed-derived Sb2S3-NA or tiny-Sb2Se3-seed-derived Sb2S3-NA growth on non-epitaxial-for-seed-growth substrates. Moreover, the homoepitaxial nucleation effect of epitaxially formed tiny seeds is specified to the tiny-Sb2S3-seed-derived Sb2S3-NA growth on TiO2 nanoparticle film. Selenization of the tiny-Sb2Se3-seed-derived Sb2S3/TiO2 nanoarray heterojunction (Sb2S3/TiO2-NHJ) renders a novel Sb2(S,Se)3/TiO2 quasi-nanoarray heterojunction (Sb2(S,Se)3/TiO2-quasi-NHJ), and a champion power conversion efficiency of 7.18% is achieved in the Sb2(S,Se)3/TiO2-quasi-NHJ solar cells with an optimized S/Se atomic ratio of ca. 1/1 obtained by the selenization at 300 °C. This paper not only demonstrates the facile solution-processing methods to prepare quality NHJ and quasi-NHJ systems for optoelectronic applications, but also is expected to guide the conceptual design for semiconductor nanorod array growth.