hujiao

One of the major challenges encountered in hydrogen evolution reaction (HER) electrocatalysis is the development of highly-efficient catalysts suitable for use in alkaline media. Tungsten carbide-based materials have long been advocated as potential alternatives to platinum (Pt) for HER process due to their “Pt-like” electronic structures. However, they exhibit significant HER activity mostly in acid but not in alkali. Herein, we report a robust synthetic method for directly growing a unique eutectoid-structured WC/W₂C heterostructure (ES-WC/W₂C) that can serve as a highly active electrocatalyst for alkaline HER via calcination of a special two-dimensional organic-inorganic tungsten precursor. This novel ES-WC/W₂C catalyst exhibits high alkaline HER activity with an ultra-low onset-potential of 17 mV and a low overpotential of 75 mV at 10 mA/cm² (ɳ₁₀). It yields an ultra-high exchange current density of 0.58 mA/cm², an enhancement of nearly 14- and 12-fold in comparison with the phase-pure WC and W₂C, respectively. Even when normalized to the electrochemically active surface area (ECSA), the normalized current density (J_{0, normalized}) is still significantly higher than the J_{0, normalized} for phase-pure WC and W₂C, demonstrating the substantial improvement of intrinsic activity by constructing such heterostructures. Moreover, it also exhibits an exceptionally stability in alkaline solutions, showing no evidence of significant degradation over 480 h (>20 days) of H₂ production, far exceeding the stability of other tungsten carbide-based electrocatalysts. To the best of our knowledge, this is the first time such a eutectoid-structured material has been reported to efficiently catalyze the HER in alkaline solution.

Bismuth-based lead-free perovskite solar cells are promising alternatives to the lead-based organic-inorganic hybrid cells which suffer from the environmental toxicity of lead and poor ambient stability, but the devices based on single-component ternary bismuth halides exhibit inferior power conversion efficiency. Herein, for the first time we construct bulk heterojunction (BHJ) bismuth-based perovskite solar cells with the photoactive layer consisting of in-situ phase-separated Cs₃Bi₂I₉ and Ag₃Bi₂I₉ components, achieving a record efficiency of approximate 3.6% and an unprecedented open-circuit voltage reaching 0.89 V. Formation of BHJ structure leads to increased crystal grain size of Cs₃Bi₂I₉ and optimized grain orientation of Ag₃Bi₂I₉, and a type-II energy band alignment is achieved, benefiting exciton separation and charge carrier transport. Cs₃Bi₂I₉–Ag₃Bi₂I₉ BHJ devices exhibit superb thermal stability, retaining ~90% of the initial efficiency after 450 h heating under 85 °C in glove box. Moreover, the universality of BHJ concept in boosting device performance of perovskite solar cells based on other reported Ag_xBi_yI_x+3y light-absorbers is verified. Our proof-of-concept breakthrough paves the way toward high-efficiency lead-free perovskite solar cells.

Fullerene and its derivatives are commonly used as electron transport layers (ETLs) in inverted perovskite solar cells (PSCs), since they show suitable band alignment and good electron mobility. However, fullerene-based ETLs typically result in low open-circuit voltages due to the interfacial defects, and they also exhibit poor photochemical and thermal stability. Consequently, there is great interest in the development of novel ETLs for high-performance inverted PSCs. In this work, two n-type polymers PBTI and PDTzTI are utilized as ETL in inverted PSCs, which are based on bithiophene imide and thienylthiazole imide, respectively. Due to its high electron mobility, well matched energy level alignment together with the passivation of interfacial traps/defects, device with the PDTzTI ETL demonstrates a best power conversion efficiency of 20.86%, which outperform those with PBTI and PCBM ETLs. Owning to the highly hydrophobic properties as well as the mobile ion blocking capability of polymer, PDTzTI ETL based device also exhibits excellent long-term and operational device stability as compared with the PCBM one. Our results demonstrate that rational selection of ETLs has great impact on the device efficiency and stability in inverted planar PSCs and that novel n-type polymer might be ideal alternative ETL in inverted planar PSCs.

Hot carriers and their extraction have been demonstrated in organic-inorganic perovskites under transient condition. Unfortunately, there was no real device to harvest hot carriers under steady-state illumination yet due to the indistinguishable hot and cooled carriers in conventional sandwiched structure. Here we report a new designed architecture based on internally photoemitted hot carrier (IPHC) solar cell, whose active CH₃NH₃PbI₃ layer is outside of the two collection electrodes with configuration of CH₃NH₃PbI₃/Au/TiO₂/FTO. Herein, the photoexcited hot electrons transfer ballistically from CH₃NH₃PbI₃ layer to TiO₂ via thin gold layer for electron collection. For the first time, the device we fabricated using this novel structure produces short circuit current of 5422 μA cm⁻² under one sun (100 mW cm⁻²) illumination which demonstrates the efficient harvesting of hot electrons under steady-state sunlight illumination. The considerable efficient photocurrent showed by this new design opens an alternative approach for light-to-electricity conversion.

Lead-acid batteries contain significant amount of lead that is an important material for emerging perovskite solar cells. Here, we successfully recovered lead from lead-acid battery. Anode and cathode lead mud reacted with acetic acid (CH₃COOH), and the produced high purity lead acetate (Pb(Ac)₂) was tested with FTIR and XRD. The simple synthetic path is efficient and causes no secondary pollution. Furthermore, the recovered lead acetate was used to fabricate normal planar heterojunction perovskite solar cells (PerSCs) with a power conversation efficiency reaching 17.83%. In addition to lead acetate, CH₃COOH was also found in the product of cathode mud. CH₃COOH is beneficial for a compact and crystalline perovskite film and improves the device performance. Fabrication of perovskite solar cells with lead from spent batteries reduces the environmental impact of battery waste and promotes the development of new energy technology.

Unstable nature against moisture is one of the major issues of metallic halide perovskite solar cell application. Thin-film encapsulation is known as a powerful approach to notably enhance the operational stability of perovskite solar cells in humid environment. However, encapsulation layers with ideal gas barrier performance always require harsh fabrication conditions with high temperature and harmful precursors. For this reason, here we provide a mild encapsulation strategy to maintain the original performance of solar cell devices by utilization of ethylene glycol-induced immediate layer to minimize the damage of plasma-enhanced atomic layer deposition to perovskite solar cells. The organic-inorganic alternating encapsulation structure has exhibited a water vapor transmittance rate of 1.3 × 10⁻⁵ g m⁻²·day⁻¹, which is the lowest value among the reported thin film encapsulation layers of perovskite solar cells. Our perovskite solar cells have survived at 80% relative humidity and 30 °C for over 2000 h while preserving 96% of its initial performance.

Perovskite solar cells (PSCs) have demonstrated high power conversion efficiencies (PCEs) but poor stability against ultraviolet (UV) irradiation. Here, we report a one-pot synthesized luminescent europium-doped titania (Eu-TiO₂) via chemical-bath deposition at low-temperature (70 °C) for planar PSCs, which enables simultaneous efficiency and UV-stability enhancement. We show that the Eu-TiO₂ could effectively convert damaging UV photons into useful visible luminescence for additional light harvesting. A more optimal energy band alignment at the Eu-TiO₂/perovskite interface leads to facilitated charge extraction and suppressed non-radiative recombination. The use of Eu-TiO₂ in PSCs results in increased photocurrent and open-circuit voltage, yielding an enhanced PCE of 21.40% with relative to pristine TiO₂ device (19.22%). More importantly, the Eu-TiO₂ devices exhibit remarkably improved UV stability, retaining 75% of the initial PCE after exposing to UV illumination for 500 h, while the devices with pristine TiO₂ lost the majority of their original PCEs in 150 h. As a proof-of-concept, we further demonstrate the scalability of our method by fabricating a large-area Eu-TiO₂ film of 64 cm² showing excellent uniformity.

Environmental instability of Spiro-OMeTAD-based hole transport layer (HTL) caused due to rapid aggregation and hydration of its additive, Lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI), gives rise to an accelerated degradation of the resulting perovskite solar cells (PSCs). Herein, we show that replacing the Li-TFSI with the more hydrophobic alkaline-earth bis(trifluoromethanesulfonyl)imide additives, namely Mg-TFSI₂ and Ca-TFSI₂, can effectively stabilize the coordination complexes between the TFSI-salts and 4-tert-Butylpyridine, which in turn results in retarded additive aggregation and hydration, enabling enhanced moisture-resistance of the subsequent HTLs. Moreover, by manipulating this substitution method, we achieved high-quality HTLs with increased hole mobility, better-formed interface with the adjacent perovskite, allowing improved hole extraction process. Incorporating these HTLs into photovoltaic devices, we obtained a substantial performance improvement, with the champion PSC yielded a power conversion efficiency of over 20%. In addition, un-encapsulated devices stabilized by the alkaline-earth bis(trifluoromethanesulfonyl)imide additive maintained 83% its initial efficiency for 193 days after aging in ambient air (RH% = 55–70%).

Inorganic cesium lead tri-bromine (CsPbBr₃) perovskite is a star material in modern optoelectronic and electronic nanodevices due to its fascinating optical and electronic properties and excellent stability in atmosphere. However, the unique dielectric behavior still remains to be exploited. Herein, inorganic CsPbBr₃ perovskite is introduced into triboelectric nanogenerators for the first time in view of its tremendous dielectric and electrical properties. Electron binding energy, dielectric properties and surface potentials are systematically optimized through doping Ba²⁺ into CsPbBr₃ lattice to form CsPb_1-xBa_xBr₃ (x = 0.01–0.13) perovskites. The output performances are significantly improved on account of enhanced space charge polarization and increased work function. An open-circuit voltage of 220 V, short-circuit current density of 22.8 mA m⁻² and maximized power density of 3.07 W m⁻² are registered by the champion CsPb_0.91Ba_0.09Br₃ based TENG with lighting up over 80 LED lights. Finally, impacts of temperature and relative humidity on the output performance of perovskite TENG are investigated, high durability and stability of the perovskite TENGs are presented indicating the remarkable reversibility and adaptability of all-inorganic CsPbBr₃ perovskites in TENG for mechanical energy harvesting.

The performance of perovskite solar cells is under direct control of the perovskite film quality and controlling the crystalinity and orientation of solution-processed perovskite film is a fundamental challenge. In this study, we present a scalable fabrication process for heteroepitaxial growth of mixed-cation hybrid perovskites (FA_1-x-yMA_xCs_y)Pb(I_1-xBr_x)₃ in ambient atmospheric condition by using a Crystal Engineering (CE) approach. Smooth and mesoporous thin film of pure crystalline intermediate phase of PbX₂.2DMSO is formed by deposition of supersaturated lead/cesium halides solution. Kinetically fast perovskite nucleation is achieved by rapid intercalation of formamidinium iodide (FAI) and methylammonium bromide (MABr) into the intermediate layer trough solvent assisted S_N1 ligand exchange. Finally, heteroepitaxially perovskite growth is accomplished via Volmer−Weber crystal growth mechanism. All the layers are deposited under atmospheric condition (relative humidity (RH) 50–75%) with high reproducibility for various device and module dimensions. In particular, perovskite solar modules (Pmax ~550 mW) are successfully fabricated by blade coating under atmospheric condition. The CE approach remarkably improves the device performance by reaching a power conversion efficiency of 18.4% for small area (0.1 cm²), 16.5% on larger area (1 cm²) devices, and 12.7% and 11.6% for blade-coated modules with an active area of 17 and 50 cm², respectively. Non-encapsulated triple cation solar cells and modules show promising stability under atmospheric shelf life and light soaking conditions.

Cesium lead halide perovskites (CsPbX₃) have become superior candidates for perspective optoelectronic applications. However, room temperature synthesized CsPbX₃ nanocrystals (NCs) suffer from serious lattice/surface traps, mostly induced by nonequilibrium reactions and polar solvent systems. Thus, direct assembly of such poor crystals cannot be available toward high efficiency light emitting diodes (LEDs). To address this issue, differing from the general post-treatment works, here we propose a double-terminal diamine bromide salt to in situ passivate the surface traps of room temperature synthesized CsPbBr₃ NCs. High-quality NC solutions with photoluminescence quantum yield (PLQY) beyond 90% are obtained owing to the renovated surface bromide vacancies. Meanwhile, instead of longer oleylamine (OLA) ligand, the abridged diamine bromine ligand could significantly enhance charge transport throughout the NC film. In addition, the NC based LED performance is found related to chain length of the ligand, where the optimal luminance of 14021 Cd m⁻² and current efficiency of 25.5 Cd A⁻¹ are achieved by 1, 4-butanediamine bromide passivated NC devices. This work provides a direct efficient approach to meet the device application of room temperature synthesized perovskite NCs, underlines the significance of selective ligands to address the challenges of NC emitters in future displays and solid-state lighting.

Single-mode microlasers are of crucial importance for high-performance integrated photonic devices. However, it still remains a significant challenge to achieve single-mode microlasers conveniently. In this work, we propose a strategy to realize high-quality, single-mode vertical-cavity surface-emitting lasers (VCSELs) based on hybrid perovskite monocrystalline films. Under two-photon pump, the VCSEL exhibits excellent performances with a remarkable low threshold of ~421 μJ/cm², a high quality factor (Q factor) of ~1286 and a small divergence angle of ~0.5°. Importantly, single-mode lasing with a good spatial coherence can be conveniently achieved with the VCSEL configuration, which significantly reduces the complexity for fabricating high-quality single-mode microlasers. In addition, switchable VCSEL can be realized by taking advantage of the anisotropic two-photon absorption of the hybrid perovskites. The single-mode vertical-cavity emission, excellent lasing performances, frequency up-conversion ability and switchable property will provide a versatile platform for high-performance nanosources and multifunctional integrated optoelectronic devices.

The defects in perovskite crystals and the penetration of moisture/oxygen into the perovskite layer are major problems for perovskite solar cells (PSCs) to achieve long-term stability and high power conversion efficiency (PCE). However, there is still a lack of multifunctional passivation materials to solve these problems. Herein, for the first time, we report oleyl amine-coated PbSO₄(PbO)₄ quantum-dots (QDs), as a passivation material with dual functions to simultaneously passivate the surface defects and block the penetration of moisture/oxygen into the perovskite layer for stable and efficient PSCs. The PbSO₄(PbO)₄ QDs significantly reduce the defect density of the as-prepared CH₃NH₃PbI₃ films by passivating under-coordinated Pb ions and I anions and effectively enhance charge extraction efficiency at the TiO₂/CH₃NH₃PbI₃ and CH₃NH₃PbI₃/spiro-OMeTAD interfaces. Moreover, the hydrogen bond between H atoms of the OA and I atoms of the perovskite and the interface electric field at CH₃NH₃PbI₃/OA interface also contribute to the improvement of efficiency and stability of PSCs. Finally, higher PCE (20.02%) is achieved by the PSCs with OA-coated PbSO₄(PbO)₄ QDs compared to that (16.86%) of the PSCs without OA-coated PbSO₄(PbO)₄, corresponding to a 18.7% enhancement. Moreover, the PSCs with OA-coated PbSO₄(PbO)₄ QDs maintain 90% of initial efficiency after operation for 280 h, indicating better stability than the PSCs without PbSO₄(PbO)₄ QDs.