Formamidinium (FA)-rich lead iodide perovskite solar cells (PSCs) are gaining popularity because of their excellent photovoltaic performance. Nevertheless, the FA-rich perovskites processed by a two-step sequential deposition method usually possess...

HIGHLIGHTS • A novel N-doped strategy of C 2 N 3 − in situ trimerization between the 2D MXene interlayers was first proposed. • The ultra-fast pseudocapacitive behavior of Ti 3 C 2 T x /Na 3 TCM anode was managed and verified. • The as-fabricated sodium-ion capacitor delivers excellent electrochemical performance by anode/cathode mass matching. ABSTRACT 2D MXenes are attractive for energy storage applications because of their high electronic conductivity. However, it is still highly challenging for improving the sluggish sodium (Na)-ion transport kinetics within the MXenes interlayers. Herein, a novel nitrogen-doped Ti 3 C 2 T x MXene was synthesized by introducing the in situ polymeric sodium dicyanamide (Na-dca) to tune the complex terminations and then utilized as intercalation-type pseudocapacitive anode of Na-ion capacitors (NICs). The Na-dca can intercalate into the interlayers of Ti 3 C 2 T x nanosheets and simultaneously form sodium tricyanomelaminate (Na 3 TCM) by the catalyst-free trimerization. The as-prepared Ti 3 C 2 T x /Na 3 TCM exhibits a high N-doping of 5.6 at.% in the form of strong TiN bonding and stabilized triazine ring structure. Consequently, coupling Ti 3 C 2 T x /Na 3 TCM anode with different mass of activated carbon cathodes, the asymmetric MXene//carbon NICs are assembled. It is able to deliver high energy density (97.6 Wh kg −1), high power output (16.5 kW kg −1), and excellent cycling stability (≈ 82.6% capacitance retention after 8000 cycles).

A series of multiheteroatom porous carbon frameworks (MPCFs) is prepared successfully from the trimerization of cyano groups of our designed and synthesized 4,4'-(4-oxophthalazine-1,3(4H)-diyl)dibenzonitrile monomers and subsequent ionothermal synthesis. Benefiting from the molecular engineering strategy, the obtained MPCFs framework show a homogeneous distribution of nitrogen and oxygen heteroatoms at the atomic level, confirmed by the transmission electron microscopy mapping intuitively, thereby ensuring the stability of electrical properties. The supercapacitor with the obtained MPCFs@700 as the electrode exhibits a high energy density of 65 Wh kg at 0.1 A g, with excellent long cycle life and cycle stability (98% capacitance retention for 10 000 cycles in 1-butyl-3-methylimidazolium tetrafluoroborate). Another two electrolyte systems employed also demonstrate the delightful results, showing a 112% capacitance retention for 30 000 cycles in 1 M HSO and a 95% capacitance retention for 30 000 cycles in tetraethylammonium tetrafluoroborate in an acetonitrile solution. Moreover, the successful preparation of MPCFs provides new insights into the fabrication of electrode materials intrinsically containing nitrogen and oxygen in the frameworks for readily available components through a facile routine.

Lithium−sulfur (Li−S) batteries have attracted a great deal of attention for the next-generation energy storage devices due to their inherently high theoretical energy density, high natural abundance, and low cost. However, the dissolution of polysulfides in electrolytes and their undesirable shuttle behavior lead to poor cycling performance, which obstructs practical application. Herein, we report a dual-sulfur-fixing mechanism of epoxy/allyl compound/sulfur system to prepare poly(sulfur-random-4-vinyl-1,2-epoxycyclohexane) (SVE) copolymers as powerful cathode materials. Benefiting from the stable C−S bond and a uniform distribution of ultrafine Li 2 S/S 8 in the SVE-based polymer matrix, the SVE electrodes exerted an embedding effect to reduce polysulfides migration. The thiosulfate/polythionate protective layer derived from the terminal hydroxyl group of SVE also ensured the cycle stability of SVE electrodes during cycling. As a result, optimized SVE electrodes deliver a high reversible specific capacity of 1248 mA h g −1 at rates of 0.1 C, together with a stable cycling performance of no capacity decay per cycle over more than 400 cycles. This work provides an effective strategy for the practical application of organosulfur polymers Li−S batteries and inspires the exploration of the reaction mechanism of epoxy/allyl compound/sulfur system.

N, S-co-doped hierarchical porous carbon with stable sodium storage were prepared by designing the precursors and changing the reaction temperature.

Sodium‐ion batteries (SIBs) hold great potential in the application of large‐scale energy storage. With the coming commercialization of SIBs, developing advanced anode of particularly hard carbon is becoming increasingly urgent yet challenging. Hard carbon still suffers from unclear sodium storage mechanism, unsatisfactory performance, and low initial Coulombic efficiency (ICE). Herein, the current state‐of‐the‐art advances in designing hard carbon anodes for high‐performance SIBs is summarized. First, the formation process of hard carbon and typical sodium storage models of “insertion–adsorption,” “adsorption–insertion,” “adsorption–pore filling,” and “adsorption–insertion–pore filling” are introduced systematically. Then, the key strategies including morphological engineering, heteroatom doping, and graphitic structure regulation are presented to enhance the capacity of hard carbon based on the in‐depth understanding of sodium storage behaviors. Subsequently, to promote the practical application of hard carbon, more attention is paid to the methods of ICE improvement, including electrolyte optimization, defect and surface engineering, and presodiation. Whereafter, hard‐carbon‐based SIBs and their intriguing applications are briefly sketched. Finally, future directions and challenging perspectives of hard‐carbon anodes for SIBs are proposed from the viewpoints of storage mechanisms, electrode structures, and presodiation techniques.

Sequential deposition has been widely employed to modulate the crystallization of perovskite solar cells because it can avoid the formation of nucleation centers and even initial crystallization in the precursor solution. However, challenges remain in overcoming the incomplete and random transformation of PbI2 films with organic ammonium salts. Herein, a unique intermediate phase engineering strategy has been developed by simultaneously introducing 2,2‐azodi(2‐methylbutyronitrile) (AMBN) to both PbI2 and ammonium salt solutions to regulate perovskite crystallization. AMBN not only coordinates with PbI2 to form a favorably mesoporous PbI2 film due to the coordination between Pb2+ and the cyano group (C≡N), but also suppresses the vigorous activity of FA+ ions by interacting with FAI, leading to the full PbI2 transformation with the preferred orientation. Therefore, perovskites with favorable facet orientations are obtained, and the defects are largely suppressed owing to the passivation of uncoordinated Pb2+ and FA+. As a result, a champion power conversion efficiency over 25% with a stabilized efficiency of 24.8% is achieved. Moreover, the device exhibits an improved operational stability, retaining 96% of initial power conversion efficiency under 1000 h continuous white‐light illumination with an intensity of 100 mW cm−2 at ≈55 °C in N2 atmosphere.

Wide bandgap (WBG) perovskites through tuning iodine/bromine ratios are capable of merging with narrow bandgap organic bulk heterojunctions to construct tandem solar cells to overcome the Shockley–Queisser limitation. However, WBG perovskites readily suffer from light‐induced halide ion migration, leading to detrimental phase segregation and hence severe open‐circuit voltage (VOC) loss. Here, to solve this issue, lead thiocyanate (Pb(SCN)2) and 2‐thiopheneethylammonium chloride (TEACl) are synergistically employed to passivate and stabilize WBG perovskites with 1.79 eV bandgap. It is demonstrated that the synergetic employment of Pb(SCN)2 and TEACl suppresses light‐induced phase segregation, passivates WBG perovskite defects, and reduces non‐radiative recombination, hence alleviating VOC loss. As a result, optimized WBG perovskite solar cells (PSCs) are obtained with an impressive VOC of 1.26 V and power conversion efficiency (PCE) over 17.0%. Furthermore, the interconnection layer is optimized to minimize the VOC loss and construct two‐terminal perovskite/organic tandem solar cells with a narrow bandgap organic blend bulk heterojunction of PM6:Y6 and achieve a champion PCE of 22.29% with a high VOC of 2.072 V. In addition, these tandem solar cells maintain 81% of their initial efficiency after 1000 h continuous tracking at the maximum power point (MPP) under 100 mW cm−2 white light illumination.