High thermoelectric figure of merit in nonplanar graphene nanoribbons with periodic divacancies

Design and implementation of high-performance thermoelectric (TE) devices pose significant challenges from both theoretical and experimental perspectives. Utilizing experimentally synthesized eight-carbon-wide armchair graphene nanoribbons with built-in periodic divacancies (DV8-aGNR), we address these challenges with three effective strategies: periodic pores, nonplanarity, and vertical junctions, all with the goal of minimizing phonon thermal conductivity and achieving a high figure of merit (<i>ZT</i>). Through first-principles calculations, we firstly investigate the TE performance of DV8-aGNR, which reveals that the periodic divacancies and nonplanar characteristics can effectively reduce phonon thermal conductivity while enhancing electrical conductance. A maximum <i>ZT</i> value of 0.64 at room temperature and 0.87 at 500 K in DV8-aGNR is 337% and 414% times that of the armchair graphene nanoribbon with the same width. Then the proposed van der Waals junction further restricts phonon transmission and exhibits improved TE properties, with <i>ZT</i> values rising to 1.70 and 1.97 at 300 and 500 K, respectively. The enhancement of <i>ZT</i> observed in DV8-aGNR and its vertical junction underscores the potential of our strategies for developing carbon-based TE devices with high performance.