Tuning the properties of armchair graphene nanoribbons via chromium doping and double vacancy engineering

• Investigated the effects of double-vacancy defects and Cr doping on the thermoelectric performance of AGNRs. • Achieved reduced thermal conductance, high electrical conductance, and a moderately enhanced Seebeck coefficient. • Improved thermoelectric efficiency for energy-harvesting applications. The thermoelectric properties of armchair graphene nanoribbons (AGNRs) have garnered significant interest due to their promising potential in energy conversion applications. However, achieving a balance between electrical conductance and thermal conductance remains a major challenge. In this study, we investigate the effects of double vacancy (DV) defects and chromium (Cr) doping on the thermoelectric performance of AGNRs using Extended Hückel theory (EHT) combined with nonequilibrium Green’s function (NEGF) formalism. Our results display that the introduction of DV defects reduces the bandgap of AGNRs, enhancing the carrier transport and creating thermally accessible electronic states. However, the most notable improvement occurs with Cr doping. Chromium atoms, introduced at various lattice sites within DV-defected AGNRs, significantly reduce the bandgap further, introduce mid-gap states, and increase electrical conductance. The interplay between Cr dopants and DV defects leads to a significant enhancement in Seebeck coefficient and a reduction in thermal conductance, resulting in improved thermoelectric performance. Specifically, a four-Cr atom configuration yields the highest thermoelectric figure of merit ZT , reaching a value of 1.93 at room temperature. This performance is driven by the combined effects of reduced the thermal conductance, high electrical conductance, and a moderately enhanced Seebeck coefficient. Additionally, the study emphasizes the importance of dopant site engineering, as Cr placement at specific lattice sites maximizes the thermoelectric efficiency by enhancing carrier delocalization without introducing excessive metallic behavior. These findings suggest that the co-engineering of defects and dopants, particularly Cr doping, offers a promising strategy for enhancing the thermoelectric performance of AGNRs. This study paves the way for future design strategies in the development of high-performance, low-power thermoelectric materials for nanoscale energy harvesting applications.