Enhancement of thermoelectric performance of n-type AgBi1+xSe2 via improvement of the carrier mobility by modulation doping

High charge carrier mobility with low lattice thermal conductivity is one of the key factors for the design of a good thermoelectric material. Recent studies show that n-type Te-free AgBiSe2 is promising compound for thermoelectric energy conversion due to intrinsically low lattice thermal conductivity. However, low charge carrier mobility in AgBiSe2 is the constraint for enhancement of its power factor. In the present study, we use a chemical modification way to realize modulation doping in AgBiSe2. The addition of 2–6 mol% excess Bi in AgBiSe2 results in the formation of Bi-rich modulation-doped microstructures of topological semimetal, Bi4Se3 in AgBiSe2 matrix. We show that due to facile carrier transport via semi-metallic Bi4Se3 microstructure results in overall improvement of carrier mobility without compromising Seebeck coefficient in AgBiSe2 system, which in turn results in a remarkable improvement in the power factor (σS2) value. A highest σS2 value of ~6.35 μW cm−1 K−2 at 800 K has been achieved in AgBiSe2-3% Bi excess sample, which is higher than previously reported metal ion and halogen-doped AgBiSe2.