SnSe single crystals have drawn extensive attention for their ultralow thermal conductivity and outstanding thermoelectric performance. Here, we report super large Sn 1-x Se single crystals with excellent thermoelectric properties, fabricated via an advanced horizontal Bridgman technique with great yield and high reproducibility. The obtained single crystals have a super large size of â70 × 50 × 15 mm with a considerable weight of 148 g, which leads to a record-high mass density of >6.1 g cm -3 . Extensive chemical characterization demonstrates that â0.3% Sn vacancies are present, which results in a large concentration of holes, â1.2 × 10 19 cm -3 , and an enhanced power factor of â6.1 μW cm -1 K -2 at 793 K. Simultaneously, the Sn-vacancy-induced lattice distortions result in a low thermal conductivity of â0.39 W m -1 K -1 at 793 K, leading to a competitive ZT of â1.24. This work demonstrates that large-size off-stoichiometric SnSe single crystals hold promise to achieve high thermoelectric performance.