Leveraging Deep Levels in Narrow Bandgap Bi0.5Sb1.5Te3for Record-HighzTaveNear Room Temperature

Deep levels in a narrow bandgap semiconductors are considered detrimental to their electrical performance. Here the constructive role of Indium-induced deep levels in regulating the majority and minority carriers for state-of-the-art average thermoelectric figure-of-meritzT(ave)between 300 and 500 K in narrow bandgap p-type (Bi,Sb)(2)Te(3)is reported. Two compositional series in the pseudo-ternary Bi2Te3-Sb2Te3-In(2)Te(3)phase diagram: Bi0.475-xSb1.525InxTe3(0 <= x <= 0.15) and Bi0.475Sb1.525-yInyTe3(0 <= y <= 0.10), namely, thex-series andy-series are explored. In thex-series, the combined experimental and theoretical study shows that Indium doping induced donor-like and acceptor-like deep levels, enlarges the band gap, and flattens the conduction band edge, thereby weakening the temperature dependence of Seebeck coefficient and the bipolar heat conduction. Further doping thex-series with copper (aka shallow acceptors) to optimize the majority carrier concentration leads to a state-of-the-artzT approximate to 1.61 at 390 K and record-high averagezT(ave) approximate to 1.47 between 300 and 500 K in p-type Bi0.396Sb1.525In0.075Cu0.004Te3. These results attest to the efficacy of deep levels in narrow bandgap thermoelectrics for both power generation and solid-state refrigeration near room temperature.