Enhanced Thermoelectric Transport Properties of 
 n
 -Type SnSe2 Polycrystalline Alloys by Te Doping

<jats:p>SnSe2, a layered posttransition metal chalcogenide, has attracted attention as a high-efficiency thermoelectric material owing to the intrinsic low thermal conductivity. Herein, a series of <jats:inline-formula> <math xmlns="http://www.w3. org/1998/Math/MathML" id="M2"> <mtext>Sn</mtext> <msub> <mrow> <mfenced open="(" close=")"> <mrow> <mtext>S</mtext> <msub> <mrow> <mtext>e</mtext> </mrow> <mrow> <mn>1</mn> <mo>−</mo> <mi>x</mi> </mrow> </msub> <mtext>T</mtext> <msub> <mrow> <mtext>e</mtext> </mrow> <mrow> <mi>x</mi> </mrow> </msub> </mrow> </mfenced> </mrow> <mrow> <mn>2</mn> </mrow> </msub> </math> </jats:inline-formula> (<jats:inline-formula> <math xmlns="http://www.w3.org/1998/Math/MathML" id="M3"> <mi>x</mi> <mo>=</mo> <mn>0</mn> </math> </jats:inline-formula>, 0.025, 0.0375, 0.075, 0.1, and 0.125) samples was synthesized to examine the influence of Te doping on electrical, thermal, and thermoelectric properties of <jats:inline-formula> <math xmlns="http://www.w3. org/1998/Math/MathML" id="M4"> <mi>n</mi> </math> </jats:inline-formula>-type SnSe2 alloys. Interestingly, carrier concentration and mobility were simultaneously increased for <jats:inline-formula> <math xmlns="http://www.w3. org/1998/Math/MathML" id="M5"> <mi>x</mi> <mo>=</mo> <mn>0.025</mn> </math> </jats:inline-formula> and 0.0375. Therefore, electrical conductivity is increased for <jats:inline-formula> <math xmlns="http://www.w3. org/1998/Math/MathML" id="M6"> <mi>x</mi> <mo>=</mo> <mn>0.025</mn> </math> </jats:inline-formula> and 0.0375 compared to that for the pristine sample, resulting in power factor increase to 0.25 mW/mK2 for <jats:inline-formula> <math xmlns="http://www.w3. org/1998/Math/MathML" id="M7"> <mi>x</mi> <mo>=</mo> <mn>0.025</mn> </math> </jats:inline-formula> by 12% at 790 K. However, reductions in the electrical conductivity were observed for the samples with <jats:inline-formula> <math xmlns="http://www.w3. org/1998/Math/MathML" id="M8"> <mi>x</mi> <mo>></mo> <mn>0.0375</mn> </math> </jats:inline-formula> due to the decrease in carrier mobility for <jats:inline-formula> <math xmlns="http://www.w3. org/1998/Math/MathML" id="M9"> <mi>x</mi> <mo>></mo> <mn>0.0375</mn> </math> </jats:inline-formula>, resulting in the decrease of power factor. The lattice thermal conductivity slightly reduced for the doped samples owing to point defects of Te and vacancies originating from Te doping. Consequently, the thermoelectric figure of merit (<jats:inline-formula> <math xmlns="http://www.w3.org/1998/Math/MathML" id="M10"> <mi>z</mi> <mi>T</mi> </math> </jats:inline-formula>) was increased to 0.45 and 0.49 for Sn(Se1.975Te0.025)2 (<jats:inline-formula> <math xmlns="http://www.w3.org/1998/Math/MathML" id="M11"> <mi>x</mi> <mo>=</mo> <mn>0.025</mn> </math> </jats:inline-formula>) and Sn(Se1.9625Te0.0375)2 (<jats:inline-formula> <math xmlns="http://www.w3.org/1998/Math/MathML" id="M12"> <mi>x</mi> <mo>=</mo> <mn>0.0375</mn> </math> </jats:inline-formula>) samples at 790 K, respectively, which was enhanced by 40% and 53% compared to that for undoped SnSe2. The enhanced electrical transport properties were validated by weighted mobility, density-of-state effective mass, and quality factor, and the reduction of the lattice thermal conductivity is analyzed by the Debye-Callaway model. </jats:p>