Inheriting Sb₂Se₃ Nanorods on Sb₂S₃ Nanorod Arrays for Effective Light Harvesting and Charge Extraction in Solar Cells

Antimony selenide (Sb2Se3) has great potential as a light-harvesting device in terms of its stability, nontoxicity, and photoelectric properties. Sb2Se3 has a one-dimensional (1D) crystal structure consisting of covalently bonded (Sb4Se6)n ribbons stacking together through van der Waals forces similar to the 1D structure of Sb2S3. This 1D anisotropic structure results in favorable electrical and optical properties for photovoltaics. Many Sb2Se3-based photovoltaic device studies have been focused on the oriental growth of a bulk Sb2Se3 layer. On the contrary, a nanorod array is more preferable for carrier directional transport due to the 1D crystal structure than a bulk thin film compared with a bulk layer. However, few studies have undertaken strategies for the preparation of 1D Sb2Se3 nanorod arrays. In this context, a facile method for the preparation of Sb2Se3 nanorod arrays on a substrate is urgently needed. In this work, we present a solvothermal method that can grow Sb2Se3 nanorods on antimony sulfide (Sb2S3) nanorod arrays enlightened by the advantages of the combination of Sb2S3 and Sb2Se3 such as a light-absorbing layer composed of a Sb2S3 nanorod array/Sb2Se3 nanorod array heterojunction for solar cells. An external quantum efficiency (EQE) at 370 nm of 75% was attained with an optimized device structure of glass-fluorine-doped tin oxide/ZnO/ZnO–ZnS/Sb2S3 nanorod array/Sb2Se3 nanorod array/poly(3-hexylthiophene-2,5-diyl)/MoOx/Ag. This was 2.5 times higher than that of a device using planar Sb2S3/planar Sb2Se3 as a light-absorbing layer. Improvement of the open-circuit voltage from 0.38 V with a planar device to 0.57 V with a nanorod array heterojunction was also confirmed, and a maximum power conversion efficiency of 1.50% was attained with an optimized nanorod array device. This research provides a facile method for the preparation of Sb2Se3 nanorod arrays and a method of combining two layers of inherited Sb2Se3 nanorods on Sb2S3 nanorod arrays compared with the bulk layers of a planar heterojunction, which provides comprehensive information for further optimization of antimony chalcogenide-based photovoltaics.