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

Abstract

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 AgBiSe 2 is promising compound for thermoelectric energy conversion due to intrinsically low lattice thermal conductivity. However, low charge carrier mobility in AgBiSe 2 is the constraint for enhancement of its power factor. In the present study, we use a chemical modification way to realize modulation doping in AgBiSe 2 . The addition of 2–6 mol% excess Bi in AgBiSe 2 results in the formation of Bi-rich modulation-doped microstructures of topological semimetal, Bi 4 Se 3 in AgBiSe 2 matrix. We show that due to facile carrier transport via semi-metallic Bi 4 Se 3 microstructure results in overall improvement of carrier mobility without compromising Seebeck coefficient in AgBiSe 2 system, which in turn results in a remarkable improvement in the power factor ( σS 2 ) value. A highest σS 2 value of ~6.35 μW cm −1 K −2 at 800 K has been achieved in AgBiSe 2 -3% Bi excess sample, which is higher than previously reported metal ion and halogen-doped AgBiSe 2