An increased presence of the {010} facet improved the performance of BiOBr for both water photooxidation and formic acid photodegradation.

High‐performance thermoelectric (TE) devices require not only a high figure of merit (ZT) but also mechanical strength and thermal stability. Here, a simultaneous enhancement of ZT as well as mechanical properties is obtained in GeTe‐based alloys by adding boron. This material is then assembled with n‐type CoSb3 skutterudite into TE modules. The improved ZT values result from the increase in charge carrier mobility due to the reduced interfacial barrier height. A peak ZT of 2.2 at 773 K can be achieved in Ge0.84Pb0.1Sb0.06TeB0.07, which shows a negligible change in the coefficient of thermal expansion upon the phase transition from the rhombohedral to the cubic phase, ensuring good thermal stability of the device. Resulting from the boron‐induced grain refinement and dispersion strengthening, the average compressive strength and Vickers hardness of Ge0.9Sb0.1TeB0.07 can be enhanced to ≈227 MPa and ≈202 Hv, respectively. The improved mechanical properties facilitate the assembly of devices and lower the interfacial contact resistance. As a synergy of increased ZT and mechanical strength, a high output power density of ≈1.76 W cm−2 at ΔT = 425 K and an energy conversion efficiency of 7.4% at ΔT = 477 K can be achieved in the TE modules.

High efficiency and environmental stability are mandatory performance requirements for commercialization of perovskite solar cells (PSCs). Herein, efficient centimeter-scale PSCs with improved stability were achieved by incorporating an additive-free 2,2′,7,7′-tetrakis­[N,N-di­(p-methoxyphenyl)­amino]-9,9′-spirobifluorene (spiro-OMeTAD) hole-transporting material (HTM) through simply substituting the usual chlorobenzene solvent with pentachloroethane (PC). A stabilized power conversion efficiency (PCE) of 16.1% under simulated AM 1.5G 1 sun illumination with an aperture of 1.00 cm2 was achieved for PSCs using an additive-free spiro-OMeTAD layer cast from PC. X-ray analysis suggested that chlorine radicals from PC transfer partially to spiro-OMeTAD and are retained in the HTM layer, resulting in conductivity improvement. Moreover, unencapsulated PSCs with a centimeter-scale active area cast from PC retained >70% of their initial PCE after ageing at 80 °C for 500 h, in contrast with less than 20% retention for control devices. Morphological and X-ray analyses of the aged cells revealed that the perovskite and HTM layers remain almost unchanged in the cells with a spiro-OMeTAD layer cast from PC whereas serious degradation occurred in the control cells. This study not only reveals the decomposition mechanism of PSCs in the presence of HTM additives but also opens up a broad range of organic semiconductors for radical doping.

The separation of electron–hole pairs has a significant influence on the photocatalytic process on semiconductors. In this work, BiOCl nanosheets with oxygen vacancies (BiOCl-OVs) have been prepared by reconstructing small hydrophobic BiOCl nanosheets. The transient photoresponse and the electron spin resonance (ESR) results prove that the separation of the charge carriers can be promoted by the oxygen vacancies via trapping the photoexcited electrons. Because of the improved charge separation and wide absorption of the solar spectrum, more photogenerated charge carriers are produced, as confirmed by the photocurrent response and the ESR measurements of the reactive oxygen species •O2 – and •OH. Consequently, BiOCl-OVs present enhanced photocatalytic properties toward NO removal. Our study illustrates the importance of the construction of vacancies for improving photocatalytic performance.

It has been reported that photogenerated electrons and holes can be directed toward specific crystal facets of a semiconductor particle, which is believed to arise from the differences in their surface electronic structures, suggesting that different facets can act as either photoreduction or photo-oxidation sites. This study examines the propensity for this effect to occur in faceted, plate-like bismuth molybdate (BiMoO), which is a useful photocatalyst for water oxidation. Photoexcited electrons and holes are shown to be spatially separated toward the {100} and {001}/{010} facets of BiMoO, respectively, by facet-dependent photodeposition of noble metals (Pt, Au, and Ag) and metal oxides (PbO, MnO , and CoO). Theoretical calculations revealed that differences in energy levels between the conduction bands and valence bands of the {100} and {001}/{010} facets can contribute to electrons and holes being drawn to different surfaces of the plate-like BiMoO. Utilizing this knowledge, the photo-oxidative capability of BiMoO was improved by adding an efficient water oxidation co-catalyst, CoO , to the system, whereby the extent of enhancement was shown to be governed by the co-catalyst location. A greater oxygen evolution occurred when CoO was selectively deposited on the hole-rich {001}/{010} facets of BiMoO compared to when CoO was randomly located across all of the facets. The elevated performance exhibited for the selectively loaded CoO/BiMoO was ascribed to the greater opportunity for hole trapping by the co-catalyst being accentuated over other potentially detrimental effects, such as the co-catalyst acting as a recombination medium and/or covering reactive sites. The results indicate that harnessing the synergy between the spatial charge separation and the co-catalyst location on the appropriate facets of plate-like BiMoO can promote its photocatalytic activity.

The heat-to-electricity conversion efficiency depends on the dimensionless figure-of-merit of materials, defined as ZT = S 2 σT/κ, where S, σ, and T are the Seebeck coefficient, the electrical conductivity, and the absolute temperature, respectively. The total thermal conductivity (κ) consists of the electronic thermal conductivity (κ e ) and the lattice thermal conductivity (κ l ). The ZT value is directly proportional to several physical para meters summarized in the so-called materials quality factor, B∝µ W /κ l , at a given carrier concentration (n), where the weighted mobility (µ W ) and κ l are determined by the transport properties of electrons and phonons, respectively. [5] Hence, it is desirable to maximize the weighted mobility and minimize the lattice thermal conductivity. Yet, similarities in performance change of thermal and electrical transport for thermoelectrics impede the improvement of B factor for high ZT, which is the key challenge in optimizing TE materials. [6] Sustained efforts have been undertaken to improve the TE properties of materials, such as band convergence, [7] resonant doping, [8] energy filtering, [9] high entropy, [10] and hierarchical microstructure engineering. [11] For polycrystalline bulk samples, the most ubiquitous defects are grain boundaries (GBs).Grain boundaries (GBs) form ubiquitous microstructures in polycrystalline materials which play a significant role in tuning the thermoelectric figure of merit (ZT). However, it is still unknown which types of GB features are beneficial for thermoelectrics due to the challenge of correlating complex GB microstructures with transport properties. Here, it is demonstrated that GB complexions formed by Ga segregation in GeTe-based alloys can optimize electron and phonon transport simultaneously. The Ga-rich complexions increase the power factor by reducing the GB resistivity with slightly improved Seebeck coefficients. Simultaneously, they lower the lattice thermal conductivity by strengthening the phonon scattering. In contrast, Ga 2 Te 3 precipitates at GBs act as barriers to scatter both phonons and electrons and are thus unable to improve ZT. Tailoring GBs combined with the beneficial alloying effects of Sb and Pb enables a peak ZT of ≈2.1 at 773 K and an average ZT of 1.3 within 300-723 K for Ge 0.78 Ga 0.01 Pb 0.1 Sb 0.07 Te. The corresponding thermoelectric device fabricated using 18-pair p-n legs shows a power density of 1.29 W cm −2 at a temperature difference of 476 K. This work indicates that GB complexions can be a facile way to optimize electron and phonon transport, further advancing thermoelectric materials.

A comprehensive survey on preparation methods of powdered or thin-film Bi-based photocatalysts is provided, comparing he diverse approaches and their advantages and limitations in the context of photocatalytic and photoelectrochemical applications.

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