Challenges and improvement pathways to develop quasi-1D (Sb1-xBix)2Se3-based materials for optically tuneable photovoltaic applications. Towards chalcogenide narrow-bandgap devices

Quasi-1D chalcogenides have shown great promises in the development of emerging photovoltaic technologies. However, most quasi-1D semiconductors other than Sb2Se3 and Sb2S3 have been seldom investigated for energy generation applications. Indeed, cationic or anionic alloying strategies allow changing the bandgap of these materials, opening the door to the development of an extended range of chalcogenides with tuneable optical and electrical properties. In this work, Bi incorporation into the Sb2Se3 structure has been proved as an effective approach to modulate the bandgap between <1.0 eV and 1.3 eV, demonstrating conversion efficiencies between 3 and 5% for 0.01 < x ≤ 0.10. However, there is a noticeable deterioration in optoelectronic parameters for x > 0.1. In order to better understand the underlying mechanisms leading to the formation of (Sb1-xBix)2Se3, and thus design specific strategies to enhance its properties, thin films with different annealing time and temperature have been synthesized and characterized. Interestingly, it has been observed that Sb2Se3 and Bi2Se3 are formed first, with Bi melting at 300 °C and diffusing rapidly towards the surface of the film. At higher temperature, the binary compounds combine to form the solid solution, however as the dwell time increases, (Sb1-xBix)2Se3 decomposes again into Bi2Se3 and Sb. This study has shown that the material is essentially limited by compositional disorder and recombination via defects. Likewise, routes have been proposed to improve morphology and uniformity of the layer, achieving efficiencies higher than 1% for x > 0.2.