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Wide-bandgap (∼1.7–1.8 eV) perovskite solar cells have attracted substantial research interest in recent years due to their great potential to fabricate efficient tandem solar cells via combining with a lower bandgap (1.1–1.3 eV) absorber (e.g., Si, copper indium gallium diselenide, or low-bandgap perovskite). However, wide-bandgap perovskite solar cells usually suffer from large open circuit voltage (Voc) deficits caused by small grain sizes and photoinduced phase segregation. Here, we demonstrate that in addition to large grain sizes and passivated grain boundaries, controlling interface properties is critical for achieving high Voc's in the inverted wide-bandgap perovskite solar cells. We adopt guanidinium bromide solution to tune the effective doping and electronic properties of the surface layer of perovskite thin films, leading to the formation of a graded perovskite homojunction. The enhanced electric field at the perovskite homojunction is revealed by Kelvin probe force microscopy measurements. This advance enables an increase in the Voc of the inverted perovskite solar cells from an initial 1.12 V to 1.24 V. With the optimization of the device fabrication process, the champion inverted wide-bandgap cell delivers a power conversion efficiency of 18.19% and sustains more than 72% of its initial efficiency after continuous illumination for 70 h without encapsulation. Additionally, a semitransparent device with an indium tin oxide back contact retains more than 88% of its initial efficiency after 100 h maximum power point tracking.

Identification of the active center is pivotal to manipulate the catalyst design for the oxygen evolution reaction. Herein, sulfur was introduced to partly occupy oxygen location in the surface structure of cobalt (II) oxide. The heterogenous ‘O-Co-S’ sites brought an enhanced oxygen evolution activity, including a five-fold intrinsic activity improvement and a reduced overpotential of 66 mV at 10 mA cm−2. Experimental and theoretical investigations reveal that the electronegativity difference between sulfur and oxygen induce the Co 3d electron accumulation along the Co-O bond. This orientated distortion optimizes the adsorption behaviors to oxygen-containing species and also favors energy band more continuous to promote electron transfer, thereby leading to improved electrochemical performance. This work provides the atomic-level understanding of the nature of active sites, which would shed light on the rational design and regulation of other material systems for advanced energy storage and conversion devices.

Herein, we report the construction of three-dimensional hollow core@shell structure composed of N-doped CNT-assembled dodecahedra core derived from ZIF-67 and Ni(OH)2 nanosheet shell as the sulfur scaffold for Li-S batteries. The obtained sulfur cathode demonstrates outstanding electrochemical performance, including a high reversible capacity (1321 mAh g−1 at 0.1 C), excellent rate capability (1030 and 753 mAh g−1 at 1 and 3 C, respectively), and superior cycling stability (611 mAh g−1 after 1000 cycles at 3 C). The enhancement in electrochemical performance can be ascribed to the unique core@shell architecture: the interconnected CNT-assembled dodecahedra core provides rapid Li+/e- transport and sufficient free space for volume change; the Ni(OH)2 nanosheet shell not only acts as a durable physical barrier, but also serves as the polar material to restrain the dissolution of polysulfides with chemical interaction. In addition, in-situ nitrogen doping in CNTs introduces rich defects and active sites for polysulfides adsorption. This work provides a promising direction for high performance Li-S batteries by coating strong polar material on carbon materials.

To maximize the photovoltaic performance of perovskite solar cells (PVSCs）by developing new hole-transport layer (HTL) materials, the precise tuning of their energy levels especially the highest occupied molecular orbital (HOMO) is highly desirable. Here, a simple binary strategy for the first time is proposed to acquire ideal HOMO level by optimizing the composition of binary blend HTLs including CZ-TA (HOMO = −5.170 eV) and CZ-STA (HOMO = −5.333 eV). By adding 10 wt% CZ-STA, the binary HTM (HOMO = −5.199 eV) based perovskite solar cells achieve a maximum power conversion efficiency of 19.85% (18.32% for CZ-TA). The introducing of S atom in CZ-STA not only downshifts HOMO level but also forms stronger Pb-S interaction with perovskites than Pb-O in CZ-TA, leading to better device performance and reduced hysteresis. Importantly, the un-encapsulated PVSCs using CZ-TA:CZ-STA (90:10, w/w) binary HTL exhibit good environment stability in ambient air, maintaining over 82% of their initial efficiency after 60 days’ storage with a relative humidity around 50%. Therefore, this strategy provides new insights on HTL development to push forward the progress of the emerging PVSCs

Sb2Se3 is a promising candidate for low toxicity, low-cost and high efficiency solar cells. Thin film solar cells employing Sb2Se3 as the absorber have achieved power conversion efficiencies of up to 6.5%. However, these solar cells are typically fabricated using rapid thermal evaporation, a fast deposition technique but suffer from entangled substrate and source temperatures. Here, we report on the fabrication of stable and efficient CdS/Sb2Se3 thin film solar cells using close-space sublimation process, which allows separate control of the source and substrate temperatures. This enables better control of Sb2Se3 film deposition and reduction of interfacial diffusion, leading to higher quality absorber films and improved device heterojunctions. Additionally, we introduced a novel low-cost material 4,4',4'',4'''-(9-octylcarbazole-1,3,6,8-tetrayl)tetrakis(N,N-bis(4-methoxyphenyl)aniline) (CZ-TA) as the hole transport layer (HTL) to create n-i-p structured devices. This CZ-TA HTL reduced the back contact resistance and promoted photogenerated carrier collection, boosting device photo conversion efficiency to 6.84%.

A carbazole-based hole-transporting material named 4,4′,4′′,4′′′-(9-octylcarbazole-1,3,6,8-tetrayl) tetrakis(N,N-bis(4-methoxyphenyl)aniline) (CZ-TA) has been developed through a one-step facile synthesis approach. The solution-processed planar perovskite solar cells (PVSCs) with 50 nm thick CZ-TA hole selective layer (HSL) contributes a power conversion efficiency of 18.32%, comparable to the most commonly used 200 nm spiro-OMeTAD (18.28%) HSLs. The improved hole extraction, transport and reduced recombination are found to endow CZ-TA-based devices with impressive fill factors over 81.0%. Importantly, the unit cost of HSL in PVSCs using CZ-TA can be as low as only 1/80 of that of spiro-OMeTAD, indicating that CZ-TA could be a promising candidate as HSLs for commercialization of the low-cost PVSC technology.

Calcium manganite (CMO) holds great potential for OER/ORR catalysis. But, the weak interaction between the oxygen intermediates and reaction sites leads to sluggish catalytic kinetics. Herein, to trigger the exceptional catalytic activity of CMO, we propose a thermal-induced MnO6 octahedral distortion strategy to advance the absorption capability of intermediate reactants. Refined structural analysis and theoretical calculation reveal that the strong Jahn-Teller distortion of MnO6 is capable of optimizing the surface electron redistribution and accelerating the electron transfer between the oxygen and Mn sites, which significantly boosts the intrinsic oxygen catalytic activities of the distorted CMO (D-CMO). Notably, the D-CMO functions as excellent bifunctional oxygen electrocatalysts and enables a high-performance solid-state Zn-air battery with satisfactory mechanical strength. Specifically, the as-assembled battery displays a remarkable open circuit voltage of 1.46 V and high peak power density of 149 mW cm−2, even outstripping noble-metal-based counterparts. Modulating the octahedral units to ignite the intrinsic oxygen catalytic activity provides enlightening clues to design perovskite-type air cathodes.

We report on compositional and morphological engineering of mixed methylammonium (MA) and formamidinium (FA) lead triiodide (MA1−xFAxPbI3) perovskite absorber layers to produce highly efficient planar and flexible perovskite solar cells (PVSCs) with reduced hysteresis. Incorporation of FA into the MAPbI3 extends the absorption edge of the perovskite to longer wavelengths, leading to enhanced photocurrent of the resultant PVSCs. Moreover, adding a small amount of lead thiocyanate (Pb(SCN)2) additive into mixed perovskite precursor solutions significantly enlarges the grain size and prolongs the carrier lifetime, leading to improved device performance. With optimal compositional and morphological engineering, the average power conversion efficiency (PCE) improves from 15.74±0.74% for pure MAPbI3 PVSCs to 19.40±0.32% for MA0.7FA0.3PbI3 PVSCs with 3% Pb(SCN)2 additive, exhibiting a high reproducibility and small hysteretic behavior. The best PVSC achieves a PCE of 20.10 (19.85)% measured under reverse (forward) voltage scan. Furthermore, the compositional and morphological engineering allowed the fabrication of efficient flexible PVSCs on indium-doped SnO2 (ITO)/polyethylene terephthalate (PET) substrates, with the best PCE of 17.96 (16.10)% with a VOC of 1.076 (1.020) V, a JSC of 22.23 (22.23) mA/cm2 and a FF of 75.10 (71.02)% when measured under reverse (forward) voltage scan. Our approach provides an effective pathway to fabricate highly efficient and reproducible planar PVSCs.

MnTe, which is comprised of earth-abundant and environmentally friendly elements, shows great potential for waste heat recovery in the moderate temperature range. However, its low carrier concentration limits its thermoelectric performance. Here, we achieved ultrahigh thermoelectric performance of MnTe by manipulating band structure and introducing SnTe nanocrystals. We found that incorporation of SnTe exerts a high band convergence in the electronic structure of MnTe, leading to remarkable enhancement of Seebeck coefficient. The Seebeck coefficient was greatly enhanced compared with previously reported doped MnTe. Furthermore, the carrier concentration can be optimized simultaneously by introducing SnTe. The large Seebeck coefficient combined with increased electrical conductivity give rise to high power factor ~1230 μWm−1 K−2. Meanwhile, SnTe nanocrystals help to achieve highly effective phonon scattering leading to markedly reduced lattice thermal conductivity. The proposed novel strategy decouples electron and phonon transport of MnTe, contributing to a record high ZT of ~1.4 at 873 K for the Mn1.06Te-2% SnTe material. Our finding promotes MnTe-based materials as a robust candidate for waste heat recovery at medium temperature.

Flexible semitransparent perovskite solar cells (PVSCs) hold promising applications on buildings and unmanned vehicles with irregular surfaces. Efficient wide-bandgap PVSCs are a determining factor for building perovskite-based tandem cells, in which energy level alignment plays significant roles in reducing nonradiative recombination loss at interfaces. Here, we report on the fabrication of efficient flexible semitransparent wide-bandgap PVSCs with gradient energy level alignments at both electron- and hole-selective contacts. We design a triple-electron-selective contact as electron transport layers with gradient Fermi level alignment with the conduction band of wide-bandgap perovskite, which consists of trans-1,2-Diaminocyclohexane-N,N,N′,N′-tetraacetic (CyDTA), tin dioxide (SnO2), and CyDTA-complexed SnO2. Moreover, an ultrathin gold layer embedded between 2,2′,7,7′-tetrakis(N,N-bis(p-methoxy-phenyl)amino)-9,9′-spirobifluorene (spiro-OMeTAD) hole transport layer and molybdenum oxide protection layer facilitates effective hole transport to the anode. We conduct comprehensive and solid simulation at both charge-selective contacts to reveal the working mechanisms. The champion flexible semitransparent 1.75 eV wide-bandgap PVSC achieves an efficiency of 15.02% with excellent light transparency of around 70% beyond the wavelength of 700 nm, enabling all-flexible perovskite/Cu(In,Ga)Se2 tandem devices with efficiencies beyond 21%.

The sodium-ion storage property in two-dimensional transition metal dichalcogenides (TMDs) is still seriously confined due to the lacking of efficient pathways for Na+ insertion, which enlightens the construction of multi-dimensional ion channels a necessary. Herein, we prepared interlayer defect, sulfur vacancy-contained ReS2 nanosheets on porous nitrogen-doped carbonized bacterial cellulose (dr-ReS2-x/NCBC). In such dual-defect configuration, the interlayer defects provide interconnected in-plane/interlamination channels for offering extra pathways of Na+ insertion/extraction and shortening ionic diffusion distance, while the sulfur vacancy could further enhance the electronic conductivity and induce more active sites for Na+ storage. Therefore, the dr-ReS2-x/NCBC anode displays an enhanced rate capacity (231.2 mAh g−1 at 5 A g−1) and a good cycling stability (187.3 mAh g−1 at 5 A g−1 after 500 cycles). Furtherly revealed by density functional theory calculations, the sodium-ion storage property is attributed to its negatively shifted binding energy for sodium ions (from −0.771 to −1.791/-1.244 eV), and alleviated structural change (from 5.8% to 3.4%/-1.6%) during sodiation/desodiation processes. The dr-ReS2-x/NCBC anode was also assembled coupling with Na3V2(PO4)3 cathode as a sodium-ion full cell for practical applications. This work is expected to offer an in-depth understanding between dual-defect engineering in TMDs-based anodes and as-enhanced sodium-storage performance.

Maximizing the surface area and the exposed active sites of Pt-based catalysts is one of the most effective strategies to improve their electrocatalytic performance. We here present an environmentally friendly construction of a two-dimensional Pt/SnO2/reduced-graphene-oxide (rGO) nanocomposite as a active and durable electrocatalyst. Initially, liquid-phase laser ablation generated highly reactive SnOx nanoparticles (NPs) were used as a precursor to transform the graphene oxide into rGO. Simultaneously, the initial amorphous-like SnOx can further crystallize into SnO2 NPs, which were uniformly anchored onto rGO sheets. Subsequently, the electrons photo-excited from semiconductor SnO2 were used as green reducing agents, which can in situ reduce the PtCl62+ ions to form ultrafine Pt NPs with an average size of about 1–2 nm that uniformly dispersed onto SnO2 NPs. Compared with Pt/rGO catalysts without SnO2 modification, the Pt/SnO2/rGO hybrid ternary catalysts not only show larger electrochemical active surface area and higher catalytic activity toward methanol oxidation, but also exhibit better long-term cycle stability and better tolerance toward CO-like species. Such significantly enhanced electrochemical performance could be attributed to the uniformly dispersed fine Pt NPs and the synergetic effect from the hybrid noble metal-semiconductor-carbon network components.

We present efficient metal oxide-free and annealing-free planar perovskite solar cells with the regular cell structure using vacuum-deposited fullerenes C 60 and C 70 as the electron-selective layers and vacuum-processed perovskites as the light absorbers. The devices with an ultrathin C 60 layer (5.5 nm) yielded an average power conversion efficiency of 14.3% and a maximum efficiency of 15.7%. The best-performing cell produced a steady-state efficiency of 14.6%. The high performance is attributed to the efficient blocking of holes and extraction of electrons by C 60 due to a favorable energy level alignment between the C 60 and the fluorine-doped tin oxide electrodes. With the realization of efficient cells, the annealing-free vacuum deposition of perovskite absorbers and C 60 or C 70 electron-selective layers and intermediate layers demonstrates its power for fabricating all-perovskite tandem solar cells.