Jiwu Xin

Multiple effects of Bi doping in enhancing the thermoelectric properties of SnTe

We studied the effect of doping with Bi on the thermoelectric properties of SnTe-based materials. Doping with Bi reduced the density of holes and increased the Seebeck coefficient over a wide temperature range as a result of modulation of the carrier concentration and an increase in the density of states effective mass. The lattice thermal conductivity was also greatly reduced as a result of the wide frequency range of phonon scattering by multiscale architectures derived from Bi doping. A maximum ZT value of c. 1.1 at 873 K was obtained in Sn0.94Bi0.06Te, an enhancement of 165% compared with the undoped sample.

New insight into InSb-based thermoelectric materials: from a divorced eutectic design to a remarkably high thermoelectric performance

As a promising mid-temperature thermoelectric (TE) material, the main obstacle to a high TE performance of the InSb compound is its high thermal conductivity. In this article, a new strategy of eutectic melting has been employed to improve the TE properties of the compound for the first time. By addition of excess Sb into the InSb matrix, an InSb–Sb eutectic structure has been introduced. When the temperature is above the melting point of the eutectic mixture, the InSb–Sb eutectic melts into a liquid phase which inhibits the propagation of transverse acoustic phonons, and the thermal conductivity is reduced drastically. Therefore, the thermoelectric performance is remarkably enhanced after the melting of the eutectic, and an unprecedented high ZT of 1.28@773 K has been achieved for the InSb1.04 sample, which is almost 3 times higher than that of the eutectic-free InSb matrix. Moreover, the Vickers hardness of the eutectic included InSb compound is higher than those of many well-established mid-temperature TE materials, and no evident hardness degradation can be detected after several melting–solidification cycles of the eutectic.

Synergistic Effect to High-Performance Perovskite Solar Cells with Reduced Hysteresis and Improved Stability by the Introduction of Na-Treated TiO2 and Spraying-Deposited CuI as Transport Layers

For a typical perovskite solar cell (PKSC), both the electron transport layers (ETLs) and hole transport materials (HTMs) play a very important role in improving the device performance and long-term stability. In this paper, we firstly improve the electron transport properties by modification of TiO2 ETLs with Na species, and an enhanced power conversion efficiency (PCE) of 16.91% has been obtained with less hysteresis. Subsequently, an inorganic CuI film prepared by a facile spray deposition method has been employed to replace the conventional spiro-OMeTAD as the HTM in PKSCs. Because of the improved transport properties at the ETL/perovskite and perovskite/HTM interfaces, a maximum photovoltaic efficiency of 17.6% with reduced hysteresis has been achieved in the PKSC with both the Na-modified TiO2 ETL and 60 nm-thick CuI layer HTM. To our knowledge, the PCE achieved in this paper is one of the highest values ever reported for the PKSC devices with inorganic HTMs. More significantly, the PKSCs exhibit an outstanding device stability, their PCE remains constant after storage in the dark for 50 days, and they can retain approximately 92% of their initial efficiency after storage even for 90 days.

Synergistic effect by Na doping and S substitution for high thermoelectric performance of p-type MnTe

Pristine MnTe is a p-type semiconductor with a relatively low hole concentration of 1018 cm−3, low electrical conductivity, and thus poor TE performance at room temperature owing to the broad direct band gap of 1.27 eV. In this study, Na2S was employed to be doped into the MnTe matrix to synergistically tune the electrical and thermal transport properties of the semiconductor via point defect engineering. On the one hand, Na substitution effectively improved the electrical transport properties by increasing the carrier concentration via the formation of acceptor-like defects, Na−Mn. On the other hand, thermal conductivities of the Na2S-doped samples were also sharply reduced via mass fluctuation and strain field fluctuation from the point defects introduced through Na doping and S substitution. Consequently, a maximum ZT of ∼1.09 was achieved for the 0.5 at% Na2S-doped sample at 873 K, which was the highest ZT value ever reported for p-type MnTe-based thermoelectric materials. Moreover, the high performance 0.5 at% Na2S-doped sample also exhibited good thermal stability and mechanical stability (Vickers microhardness) of ∼122 Hv, which was higher than those of other promising thermoelectric materials such as Bi2Te3, PbTe, PbSe, Cu2Se, and SnTe.

Low-Temperature Solution-Processed ZnSe Electron Transport Layer for Efficient Planar Perovskite Solar Cells with Negligible Hysteresis and Improved Photostability

For a typical perovskite solar cell (PKSC), the electron transport layer (ETL) has a great effect on device performance and stability. Herein, we manifest that low-temperature solution-processed ZnSe can be used as a potential ETL for PKSCs. Our optimized device with ZnSe ETL has achieved a high power conversion efficiency (PCE) of 17.78% with negligible hysteresis, compared with the TiO2 based cell (13.76%). This enhanced photovoltaic performance is attributed to the suitable band alignment, high electron mobility, and reduced charge accumulation at the interface of ETL/perovskite. Encouraging results were obtained when the thin layer of ZnSe cooperated with TiO2. It shows that the device based on the TiO2/ZnSe ETL with cascade conduction band level can effectively reduce the interfacial charge recombination and promote carrier transfer with the champion PCE of 18.57%. In addition, the ZnSe-based device exhibits a better photostability than the control device due to the greater ultraviolet (UV) light harvesting of the ZnSe layer, which can efficiently prevent the perovskite film from intense UV-light exposure to avoid associated degradation. Consequently, our results present that a promising ETL can be a potential candidate of the n-type ETL for commercialization of efficient and photostable PKSCs.

Combination of Carrier Concentration Regulation and High Band Degeneracy for Enhanced Thermoelectric Performance of Cu3SbSe4

The effect of Al-, Ga-, and In-doping on the thermoelectric (TE) properties of Cu3SbSe4 has been comparatively studied on the basis of theoretical prediction and experimental validation. It is found that tiny Al/Ga/In substitution leads to a great enhancement of electrical conductivity with high carrier concentration and also large Seebeck coefficient due to the preserved high band degeneracy and thereby a remarkably high power factor. Ultimately, coupled with the depressed lattice thermal conductivity, all three elements (Al/Ga/In) substituted samples have obtained a highly improved thermoelectric performance with respect to undoped Cu3SbSe4. Compared to the samples at the same Al/In doping level, the slightly Ga-doped sample presents better TE performance over the wide temperature range, and the Cu3Sb0.995Ga0.005Se4 sample presents a record high ZT value of 0.9 among single-doped Cu3SbSe4 at 623 K, which is about 80% higher than that of pristine Cu3SbSe4. This work offers an alternative approach to boost the TE properties of Cu3SbSe4 by selecting efficient dopant to weaken the coupling between electrical conductivity and Seebeck coefficient.

An in situ eutectic remelting and oxide replacement reaction for superior thermoelectric performance of InSb

In this work, we demonstrate a synergistic approach to improve the thermoelectric performance of the InSb compound by introducing a replacement reaction of InSb and TiO2 during a hot pressing process. As a consequence of the replacement reaction, TiIn+ point defects, In2O3, stacking faults and InSb–Sb eutectic structures have been introduced into the InSb matrix. Accordingly, the electrical conductivity and the power factor (PF) have been significantly improved due to the electron donating nature of TiIn+ point defects, and the thermal conductivity has also been greatly reduced owing to the extra phonon scattering by dispersed In2O3 nanoparticles and stacking faults. More importantly, the melt of the introduced InSb–Sb eutectic structures plays an important role in filtering the transverse acoustic phonons, causing an abrupt reduction of lattice thermal conductivity at high temperature (753–773 K). Therefore, a relatively high ZT value ∼1.1 at 773 K has been obtained for the 0.1 wt% TiO2 added InSb sample. Moreover, the Vickers hardness of InSb also increases largely (∼210 Hv) deriving from the strengthening effects by introduced point defects and nanoinclusions, which is tougher than many well established mid-temperature TE materials.

A new method for simultaneous measurement of Seebeck coefficient and resistivity

A new method has been proposed and verified to measure the Seebeck coefficient and electrical resistivity of a sample in the paper. Different from the conventional method for Seebeck coefficient and resistivity measurement, the new method adopts a four-point configuration to measure both the Seebeck coefficient and resistivity. It can well identify the inhomogeneity of the sample by simply comparing the four Seebeck coefficients of different probe combinations, and it is more accurate and appropriate to take the average value of the four Seebeck coefficients as the measured result of the Seebeck coefficient of the sample than that measured by the two-point method. Furthermore, the four-point configuration makes it also very convenient to measure the resistivity by using the Van der Pauw method. The validity of this method has been verified with both the constantan alloy and p-type Bi2Te3 semiconductor samples, and the measurement results are in good agreement with those obtained by commercial available equipment.