<p> 1 Supplementary information</p><p>2Band Structure Engineering and Thermoelectric Properties of Charge-Compensated Filled</p><p>3 Skutterudites</p><p>4 Xiaoya Shi1, Jiong Yang2, Lijun Wu1, a, James R. Salvador3, b, Cheng Zhang1, William L. 5 Villaire4, Daad Haddad3, Jihui Yang2, Yimei Zhu1, and Qiang Li1, c </p><p>6 1 Condensed Matter Physics and Materials Science Department, 7 Brookhaven National Laboratory, Upton, New York 11973, USA</p><p>8 2 Materials Science & Engineering Department 9 University of Washington, Seattle, WA 98195, USA</p><p>10 3 Chemical and Materials Systems Lab 11 General Motors R&D Center, Warren, MI 48090, USA</p><p>12 4 Fuel Systems Engineering 13 General Motor Global Design, Engineering and Product Programs 14 Warren, MI 48090-9020 15 Nominal Composition EMPA Composition Lattice parameter (Å)</p><p>Ga0.20Co4Sb11.9333 9.0393 Yb0.05 Ga0.20Co4Sb11.9333 9.0414 Yb0.10 Ga0.20Co4Sb11.9333 9.0435 Yb0.15 Ga0.20Co4Sb11.9333 9.0463 Yb0.20 Ga0.20Co4Sb11.9333 9.0494 Yb0.26 Ga0.20Co4Sb11.9333 Yb0.24 Ga0.15Co4Sb11.87 9.0527 Yb0.20 Co4Sb12 Yb0.18 Co4Sb11.71 9.0523</p><p>Yb0.20 Ga0.10Co4Sb11.9666 Yb0.18 Ga0.08Co4Sb11.63 9.0499 Yb0.20 Ga0.15Co4Sb11.95 Yb0.18 Ga0.13Co4Sb11.65 9.0498 Yb0.25 Ga0.15Co4Sb11.95 Yb0.23 Ga0.14Co4Sb11.50 9.0493 Yb0.30 Ga0.15Co4Sb11.95 Yb0.29 Ga0.14Co4Sb11.50 9.0525 Yb0.35 Ga0.15Co4Sb11.95 Yb0.31 Ga0.14Co4Sb11.53 9.0553 Yb0.40 Ga0.15Co4Sb11.95 Yb0.38 Ga0.14Co4Sb11.47 9.0592</p><p>16 Supplementary Table 1. Nominal composition, EMPA composition and lattice</p><p>17parameters. Samples are YbxGa0.2Co4Sb11.9333 (x = 0, 0.05, 0.10, 0.15, 0.20, 0.26),</p><p>18YbyGa0.15Co4Sb11.95 (y = 0.25, 0.30, 0.35, 0.40) and Yb0.20GazCo4Sb12-z/3 (z = 0, 0.10, 0.15) at room</p><p>19temperature for all the samples.</p><p>20 21 22Supplementary Figure 1. EPMA mapping results of the sample Yb0.30Ga0.15Co4Sb11.95. With</p><p>23the exception of Yb the maps above are very uniform indicating a homogenous distribution of</p><p>24the elements with very little to no oxide content. EPMA also finds that all four constituent</p><p>25elements are present in each grain. </p><p>26 27Supplementary Figure 2. First-principles band structure calculations. The left is </p><p>28Ga0.25Co4Sb12 and the right is In0.25Co4Sb12, assuming the IIIA atoms are all at filler sites. The zero</p><p>29energy points represent the Fermi levels (EFs) of the two compounds.</p>