Substrate dependence on (Sb4Se6)n ribbon orientations of antimony selenide thin films: Morphology, carrier transport and photovoltaic performance

In recent years, antimony selenide (Sb2Se3) has shown great potential as a photoactive material for thin film solar cells. To understand the growth mechanism and carrier transport behavior of Sb2Se3 thin films with the 1D crystal structure, the structure, properties, and photovoltaic performance of Sb2Se3 thin films with different preferred orientations were systematically characterized. The results show that Sb2Se3 thin films’ microstructure is mainly determined by the competing lateral and vertical growth of (Sb4Se6)n ribbons. As the (Sb4Se6)n ribbons’ lateral growth proportion becomes more significant, the thin film gets a flatter surface and denser microstructure, but the vertical carrier transport capability is correspondingly weaker. In contrast, when (Sb4Se6)n ribbons are dominated by the vertical growth mode, Sb2Se3 thin films tend to form an arranged nanorods structure. This structure has excellent vertical carrier transport capability; however, it also inevitably leads to increased carrier recombination due to the abundant grain boundary. As the deposition of the Sb2Se3 thin film gradually changes from the lateral growth to the vertical growth, the solar cell performance could be improved due to the enhancement of carrier transport. However, when the vertical growth ratio is too high, the fill factor of the device will reduce due to the increase of the leakage current. We demonstrate that the regulation of lateral and vertical growth proportion in Sb2Se3 photoactive layers is essential to yielding an efficient solar cell.