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The high thermoelectric performance of dopant-free, low-cost and eco-friendly p-type Zn1−xSb (x = 0, 0.01, 0.03, and 0.06) is demonstrated by synergistically optimizing its electrical and thermal properties via Zn-vacancy engineering. Upon increasing Zn-vacancies in ZnSb, the bandgap is observed to reduce due to the formation of the impurity states above the valence band, which is theoretically validated using density functional theory (DFT). Remarkably, Zn vacancy-driven point defects significantly influence the hole concentration within the Zn1−xSb samples. At 300 K, the hole concentration (nH) is boosted from 3.6 × 1018 cm−3 (in ZnSb) to 3.4 × 1019 cm−3 for the Zn0.94Sb sample, culminating in a marked enhancement in electrical conductivity (σ) from 1.80 × 104 S m−1 to 7.57 × 104 S m−1 for Zn0.94Sb. Equally noteworthy is the substantial decrease in thermal conductivity (κ) observed in the Zn0.94Sb sample at 673 K, plunging from 2.29 W m−1 K−1 (in ZnSb) to 1.41 W m−1 K−1. This decline in thermal conductivity is attributed to the effective phonon scattering arising from Zn-vacancy-assisted point defects, combined with the efficient coupling of optical and acoustic phonons and the characteristic low group velocity, evidenced by the theoretically calculated phonon dispersion curve. Overall, the high thermoelectric figure of merit, zT of ∼0.8 at 673 K, is achieved for the sample with a 6 mol% Zn deficiency. Furthermore, a maximum theoretical conversion efficiency of ∼7% is predicted at a temperature gradient of 625 K, showing high potential for use in practical devices for mid-temperature applications, and the present work features the effect of a reliable dopant-free approach in improving the overall zT of eco-friendly and low-cost ZnSb. [ABSTRACT FROM AUTHOR]

Thermoelectric generators (TEGs) have received a great attention in the field of renewable energy resources due to their superior ability of converting untapped waste heat into usable electricity. In order to boost the conversion efficiency of TEG and to retrieve the transient heat, this paper demonstrates the role of nanostructured graphite (G) and graphene oxide (GO) decorated phase-change material (PCM) of D-mannitol attached with the hot end of commercial thermoelectric module on enhancement of conversion efficiency and power output. Presence of G and GO on the matric of D-mannitol has been confirmed by powder XRD and FE-SEM. The open circuit voltage ( V oc ) and short circuit current ( I sc ) of TEG attached with PDM, G/PDM, and GO/PDM were recorded for the heating and cooling cycles in the temperature range of 325-450 K. Particularly, the experimentally measured V oc and I sc of TEG with only PDM are 1.23 V and 90 mA, respectively, for the temperature difference of ΔT ∽ 118 K, whereas the maximum V oc of TEG attached with GO/PDM drawn in presence of an external heater is 4.5 V for ΔT ∽ 118 K. Further, the maximum output power of TEG with GO-PCM drawn in the heater-ON and heater-OFF is 1012.5 mW and 450 mW, respectively. [ABSTRACT FROM AUTHOR]