Influence of Bismuth Substitution with Nb, Y, and P Elements on the Electronic Structure of Vacancy Filled BiCuSeO-Based System for the Thermoelectric Application

Thermoelectric materials allow a direct conversion of waste heat into electric energy. Oxiselenide-based materials are promising candidates to be used within the temperature range between room temperature and 500°C. Specifically, p-type BiCuSeO is considered to be one of the most promising materials for these applications. However, the intrinsic properties of this compound are not sufficient for reaching an efficiency above 30%. There are numerous approaches to improve the heat-to-electricity conversion performance, such as element substitution, nanostructuring, vacancies implementation, and others. Usually, these approaches are applied individually, starting from the pure intrinsic material. Higher performance could, however, be reached by combining a few strategies simultaneously or in sequence. In the current work, yttrium, niobium, and phosphorous substitutions on the bismuth sites in already bismuth deficient Bi1-xCuSeO systems were investigated via density functional theory. The bismuth-deficient system was therefore used as the reference system for further introduction of substitutional defects. The results show an improved density of states near the Fermi level for all types of substitutional defects. The substitution with phosphorous showed a up to 40 meV (11%) decrease in the energy gap between conduction and valence bands at the highest substitution concentration. Doping with niobium led to the system changing from a p-type to an n-type conductor, which provides a possible route to obtain n-type BiCuSeO systems.