Sb deficiencies control hole transport and boost the thermoelectric performance of p-type AgSbSe₂

Abstract

Electronic supplementary information (ESI) available: thermal diffusivity and heat capacity (Fig. S1), Lorentz numbers (Fig. S2), electronic thermal conductivity (κ ele ) (Fig. S3), heating cooling cycle electrical conductivity (σ) and seebeck coefficient (S) data for AgSb 0.9925 Se 2 sample (Fig. S4).Abstract: Silver antimony selenide, AgSbSe 2 , a Te free analogue of AgSbTe 2 , is known to show promising thermoelectric performance when it was doped with monovalent (M + ) and divalent (M 2+ ) cation in the Sb sublattice. Here, we report a significant enhancement of the thermoelectric performance of p-type nonstoichiometric AgSbSe 2 through Sb deficiencies. Sb deficiencies markedly increase the carrier concentration in AgSbSe 2 without addition of any foreign dopant, which in-turn enhance electrical conductivity in the 300-610 K temperature range. Enhancement in the electrical transport results in a remarkable improvement in the power factor (σS 2 ) value up to ~6.94 μW/cmK 2 at 610 K in AgSb 1-x Se 2 . Notably, we have achieved nearly flat σS 2 of ~6 μW/cmK 2 in the 400-610 K temperature range in Sb deficient samples. Additionally, AgSbSe 2 exhibits ultra-low thermal conductivity due to phonon scattering from bond anharmonicity and disordered cation sub-lattice. With superior electronic transport and ultra-low thermal conductivity, a peak zT value of ~1 at 610 K was achieved for AgSb 0.9925 Se 2 and AgSb 0.99 Se 2 samples. A maximum thermoelectric conversion efficiency (η max ) of ~8% was calculated by considering virtual thermoelectric module consisting of present p-type AgSb 1-x Se 2 and previously reported n-type AgBiSe 2-x Cl x , with maintaining a temperature different of ΔT = 400 K.

Thermoelectric optimization of AgBiSe2 by defect engineering for room-temperature applications

“…1, the formation energy of a charged defect depends on the Fermi energy level E F , which is varying within the band gap. Our theoretically calculated band gap of the pristine AgBiSe2 is 0.69 eV, which is in good agreement with the experimentally measured value (~0.6 eV) [24]. We here take the experimentally measure ~0.6 eV to constrain the E F region (using the theoretically calculated 0.69 eV does not affect our conclusions).…”

“…1 to calculate the defect formation energy in AgBiSe2, we should firstly determine the chemical potential of each element. Due to the complex phase transitions and the appearance of secondary phases, previous experimental works suggested that it is difficult to synthesize pure hexagonal phase of AgBiSe2 [24]. However, carefully controlling the chemical potential during experimental synthesis may solve the problem.…”

“…AgBiSe2 crystallizes in a hexagonal structure at room temperature. It undergoes two structural phase transitions [24][25][26][27][28][29] at a higher temperature, ~460 K (hexagonal to rhombohedral) and ~580 K (rhombohedral to cubic). AgBiSe2 has the intrinsic low lattice thermal conductivity (0.45 W/mK at 300 K [30,31]).…”

1D/3D Alloying Induced Phase Transition in Light Absorbers for Highly Efficient Sb2Se3 Solar Cells

“…The net carrier density for the (Sb 2 Se 3 ) x (AgSbSe 2 ) 1− x (320 °C) solar cell is 9.36 × 10 16 cm −3 , which is about one order of magnitude higher than that of the reference device (8.42 × 10 15 cm −3 ) (Figure S4, Supporting Information). This huge increase in carrier density could be attributed to the incorporation of the ternary AgSbSe 2 in the films, as the carrier density was able to reach values as high as 10 19 cm −3 , due to the high‐order degree of Ag and Sb sites in its cubic rock‐salt structure . We also found that the V bi values significantly increase from 0.44 to 0.51, 0.76, 0.78, and 0.83 eV for the reference device and the devices with alloy absorbers formed at 280, 320, 350, and 420 °C (Figure c), respectively.…”

Influence of the temperature and composition on the crystal structure of the AgBiSe2‐AgBiS2 system

“…Therefore, the thermoelectric figure of merit ZT, defined as (with S the Seebeck coefficient, σ the electrical conductivity, λ the thermal conductivity and T the absolute temperature), which constitutes the main criterion to evaluate the performances of thermoelectric materials, reaches promising values upon relevant doping. For example, ZT = 1 has been observed in Nb‐doped AgBiSe 2 or Cl‐doped AgBiSeS , ZT = 0.9 in Cl‐doped AgBiSe 2 , or ZT = 0.7 in In‐doped AgBiSe 2 around 500–550°C.…”