Defect Compensation Weakening Induced Mobility Enhancement in Thermoelectric BiTeI by Iodine Deficiency

Carrier mobility (weighted mobility more specifically) of thermoelectrics fundamentally determines its power factor, representing a new cut-in point to optimize the thermoelectric performance. However, researches on enhancing the carrier mobility to improve power factor has been overlooked. In present work, we highlight a significant mobility enhancement in BiTeI by introducing I deficiency, which improves the power factor and final ZT value. A defect compensation weakening mechanism is adopted that the induced I vacancies reduce the concentration of intrinsic $I_{\mathrm{Te}}^{{}^{•}}$ and ${\mathrm{Te}}_I^{{}^{\text{'}}}$ antisite defects, which weakens the donor-acceptor defect compensation and suppresses the defects-induced carrier scattering. As a result, the carrier mobility is obviously enhanced in I-deficient samples, which ensures an effectively improved power factor and final ZT. A maximum ZT of 0.57 is achieved at 570 K perpendicular to the pressing direction, which is superior to pristine BiTeI and among the highest values reported for bulk BiTeI-based thermoelectric materials. Present work opens up a new avenue for thermoelectric optimization mainly by mobility enhancement.