Wenjuan Yang

Wide-bandgap (WBG) perovskite has demonstrated great potential in perovskite-based tandem solar cells. The power conversion efficiency (PCE) of such devices has surpassed 34%, signifying a new era for renewable energy development. However, the ion migration reduces the stability and hinders the commercialization, which is yet to be resolved despite many attempts. A big step forward has now been achieved by the simulation method. The detailed thermodynamics and kinetics of the migration process have been revealed for the first time. The stability has been enhanced by more than 100% via the heterojunction layer on top of the WBG perovskite film, which provided extra bonding for kinetic protection. Hopefully, these discoveries will open a new gate for WBG perovskite research and accelerate the application of perovskite-based tandem solar cells.

This investigation is motivated by increasing interest in the development of magnetically ordered pseudocapacitors (MOPC), which exhibit interesting magnetocapacitive effects. Here, advanced pseudocapacitive properties of magnetic CuFe₂O₄ nanoparticles in negative potential range are reported, suggesting that CuFe₂O₄ is a promising MOPC and advanced negative electrode material for supercapacitors. A high capacitance of 2.76 F cm⁻² is achieved at a low electrode resistance in a relatively large potential window of 0.8 V. The cyclic voltammograms and galvanostatic charge–discharge data show nearly ideal pseudocapacitive behavior. Good electrochemical performance is achieved at a high active mass loading due to the use of chelating molecules of ammonium salt of purpuric acid (ASPA) as a co-dispersant for CuFe₂O₄ nanoparticles and conductive multiwalled carbon nanotube (MCNT) additives. The adsorption of ASPA on different materials is linked to structural features of ASPA, which allows for different interaction and adsorption mechanisms. The combination of advanced magnetic and pseudocapacitive properties in a negative potential range in a single MOPC material provides a platform for various effects related to the influence of pseudocapacitive/magnetic properties on magnetic/pseudocapacitive behavior.

The high theoretical capacitance of MnO₂ renders it a promising material for the cathodes of asymmetric supercapacitors. The good dispersion of MnO₂ and conductive additives in a nanocomposite electrode is a key factor for efficient electrode performance. This article describes, for the first time, the application of rhamnolipids (RL) as efficient natural biosurfactants for the fabrication of nanocomposite MnO₂-carbon nanotube electrodes for supercapacitors. RL act as co-dispersants for MnO₂ and carbon nanotubes and facilitate their efficient mixing, which allows for advanced capacitive properties at an active mass of 40 mg cm⁻² in Na₂SO₄ electrolytes. The highest capacitance obtained from the cyclic voltammetry data at a scan rate of 2 mV s⁻¹ is 8.10 F cm⁻² (202.6 F g⁻¹). The highest capacitance obtained from the galvanostatic charge–discharge data at a current density of 3 mA cm⁻² is 8.65 F cm⁻² (216.16 F g⁻¹). The obtained capacitances are higher than the capacitances of MnO₂-based electrodes of the same active mass reported in the literature. The approach developed in this investigation is simple compared to other techniques used for the fabrication of electrodes with high active mass. It offers advantages of using a biocompatible RL biosurfactant.

The purpose of this investigation was the development of a new colloidal route for the fabrication of Mn₃O₄ electrodes for supercapacitors with enhanced charge storage performance. Mn₃O₄-carbon nanotube electrodes were fabricated with record-high capacitances of 6.67 F cm⁻² obtained from cyclic voltammetry tests at a scan rate of 2 mV s⁻¹ and 7.55 F cm⁻² obtained from the galvanostatic charge–discharge tests at a current density of 3 mA cm⁻² in 0.5 M Na₂SO₄ electrolyte in a potential window of 0.9 V. The approach involves the use of murexide as a capping agent for the synthesis of Mn₃O₄ and a co-dispersant for Mn₃O₄ and carbon nanotubes. Good electrochemical performance of the electrode material was achieved at a high active mass loading of 40 mg cm⁻² and was linked to a reduced agglomeration of Mn₃O₄ nanoparticles and efficient co-dispersion of Mn₃O₄ with carbon nanotubes. The mechanisms of murexide adsorption on Mn₃O₄ and carbon nanotube are discussed. With the proposed method, the time-consuming electrode activation procedure for Mn₃O₄ electrodes can be avoided. The approach developed in this investigation paves the way for the fabrication of advanced cathodes for asymmetric supercapacitors and multifunctional devices, combining capacitive, magnetic, and other functional properties.

This investigation addresses the challenges in the development of efficient nanostructured Mn₃O₄ cathodes for supercapacitors. A high areal capacitance and the ability to avoid a time-consuming activation procedure for electrodes with high active mass loading of 40 mg cm⁻² are reported. This facilitates practical applications of Mn₃O₄ based electrodes. The highest capacitance of 6.11 F cm⁻² (153 F g⁻¹) is obtained from cyclic voltammetry at a scan rate of 2 mV s⁻¹ and 6.07 F cm⁻² (151.9 F g⁻¹) from the chronopotentiometry at a current density of 3 mA cm⁻² in a potential window of 0.9 V in a neutral Na₂SO₄ electrolyte. The new approach is based on the application of rhamnolipids (RL) as a capping agent for the synthesis of Mn₃O₄ particles and a co-dispersant for Mn₃O₄ and carbon nanotubes, which are used as conductive additives. The size and shape of the Mn₃O₄ particles are influenced by RL. The enhanced performance of the electrodes is linked to the chemical structure and properties of RL molecules, which exert influence on Mn₃O₄ particle size and shape during synthesis, reduce agglomeration, facilitate RL adsorption on Mn₃O₄ and carbon nanotubes, and influence their co-dispersion and mixing at the nanometric scale.

The commonly-employed methylammonium-based perovskites are environmentally unstable, which limits their commercialization. To resolve this problem, a stable hybrid perovskite, pyrrolidinium lead iodide (PyPbI₃), was synthesized successfully via a simple drop casting method. The formed PyPbI₃ exhibited a hexagonal structure. It presented not only excellent phase stability, but also low trap-state density, as confirmed via the X-ray diffraction and space-charge-limited currents measurements. This novel perovskite may be applicable to perovskite photovoltaics to improve their environmental stability.

The linear range of the non-enzymatic glucose sensor is usually much smaller than the glucose level of diabetic patients, calling for an effective solution. Despite many previous attempts, none have solved the problem. Such a challenge has now been conquered by raising the NaOH concentration in the electrolyte, where amperometry, X-ray diffraction, Fourier-transform infrared spectroscopy, and Nuclear magnetic resonance measurements have been conducted. The linear range has been successfully enhanced to 40 mM in 1000 mM NaOH solution, and it was also found that NaOH affected the degree of glucose oxidation, which influenced the current response during sensing. It was expected that the alkaline concentration must be 25 times higher than the glucose concentration to enhance the linear range, much contrary to prior understanding.

Extra peaks have constantly been observed in the X-ray diffraction measurement for the CH₃NH₃PbI₃ film. Such mysteries have now been uncovered in this paper, in which powder X-ray diffraction, in situ X-ray diffraction, and scanning electron microscopy measurements were conducted, and these peaks were attributed to the ethylammonium lead iodide (CH₃CH₂NH₃PbI₃/EAPbI₃). It was found that the formation of EAPbI₃ was triggered by the breakdown of N, N-dimethylformamide (DMF), which was adopted as the solvent in the preparation of the precursor solutions. EAPbI₃ was generated by the organic cation exchange reaction in the subsequent annealing process. A simple solution for this problem is proposed in this paper as well, which would hopefully help the community to eradicate this impurity.