Lixin Chen

Strategic improvement of the long-term stability of perovskite materials and perovskite solar cells

Perovskite solar cells (PSCs) have gained tremendous research interest in recent several years. To date the power conversion efficiency (PCE) of PSCs has been increased from 3.8% to over 22.1%, showing that they have a promising future as a renewable energy resource to compete with conventional silicon solar cells. However, a crucial challenge of PSCs currently is that perovskite materials and PSCs have limitations of easy degradation and inferior long-term stabilities, thus hampering their future commercial applications. In this review, the degradation mechanisms for instable perovskite materials and their corresponding solar cells are discussed. The stability study of perovskite materials and PSCs from the aspect of experimental tests and theoretical calculations is reviewed. The strategies for enhancing the stability of perovskite materials and PSCs are summarized from the viewpoints of perovskite material engineering, substituted organic and inorganic materials for hole transportation, alternative electrodes comprising mainly carbon and its relevant composites, interfacial modification, novel device structure construction and encapsulation, etc. Various approaches and outlooks on the future direction of perovskite materials and PSCs are highlighted. This review is expected to provide helpful insights for further enhancing the stability of perovskite materials and PSCs in this exciting field.

The Effect of Introducing B and N on Pyrolysis Process of High Ortho Novolac Resin

In this contribution, high ortho novolac resins modified with phenylboronic acid were synthesized. The thermal stability of novolac resins cured with hexamethylenetetramine (HMTA) and chemical states of B and N via a pyrolysis process were studied. For the cured o-novolac modified with phenylboronic acid, the temperature with maximum decomposition rate increased by 43.5 °C, and the char yield increased by 5.3% at 800 °C compared with cured o-novolac. Density functional theory (DFT) calculations show the existence of hydrogen bonding between N of HMTA and H of phenol in modified resin. Thus, N could still be found at high temperature and C=N structure could be formed via a pyrolysis process. B2O3 was obtained at 400 °C by the cleavage of B–O–C and B–C bonds and it reduces the oxygen loss which may take part in the formation of carbon oxides in the system. The melting B2O3 on the surface of the resin will prevent small molecules and carbon oxides from releasing. Moreover, introducing B into the system helps to decrease the interlayer distance and improve graphite structures via a pyrolysis process.

Enhanced thermal stabilities and char yields of carbon fibers reinforced boron containing novolac phenolic resins composites

Abstract4-hydroxymethyl phenylboronic acid (4-HMPBA), phenol and formaldehyde were for the first time to synthesize boron containing novolac phenolic resins (Novolac-4-HMPBA). Its corresponding carbon fibers (CF) composites were also fabricated via the lamination followed by hot-compression. Results revealed that Novolac-4-HMPBA was successfully synthesized. Compared to common novolac phenolic resin (NPR), the corresponding decomposition temperature of 5% weight loss (T5) and char yield at 800xa0°C (C800) of cured Novolac-4-HMPBA-30 were increased to 369.1xa0°C and 69.7%, increased by 41.3% and 26.3%, respectively. The CF/Novolac-4-HMPBA-20 composites presented relatively higher interlaminar shear strength (ILSS) of 35.9xa0MPa, increased by 50.2% compared to that of CF/NPR composites. After the treatment at 800xa0°C for one hour under Ar atmosphere, the corresponding ILSS value of CF/Novolac-4-HMPBA-20 composite was decreased to 7.8xa0MPa, but still higher than that of CF/NPR composites (3.0xa0MPa).

Solid-state synthesis of ZnO nanorods coupled with reduced graphene oxide for photocatalytic application

ZnO is an excellent semiconductor material for photocatalytic application. To overcome the photocorrosion of ZnO and improve its stability, nanorods (NRs) structured ZnO is prepared by an environment-friendly solid state synthesis method, and the composite of ZnO with different mass ratio of reduced graphene oxide (RGO) are obtained via a hydrothermal reaction. According to the photocatalytic results, 5% RGO composited with ZnO NRs degrades the methylene orange solution completely (98%) in 50xa0min under UV light irradiation, whereas bare ZnO NRs just degrade 40.9%. The transient photocurrent responses and electronical impedance spectroscopy tests are carried out to illustrate the mechanism of RGO in the nanocomposite for the enhancement of the photocatalytic performance. This composite of ZnO/RGO has demonstrated a great potential for high efficient and stable photocatalytic application.

Synthesis and structure evolution of phenolic resin/silicone hybrid composites with improved thermal stability

Phenolic resin/silicone hybrid composites (MPR) were prepared by a facile and low-cost method. FTIR results show that polycondensation of siloxane occurs in the presence of catalyst and water in the system, and siloxane oligomer was formed. During the curing process, the transesterification reaction between siloxane oligomer and phenolic resin (PR) makes silicon incorporated into PR. The TGA results indicate that introducing Si–O structure into PR can effectively improve the thermal stability of the resin. Compared with cured neat PR, temperatures at 5 and 10% mass loss of cured MPR can be improved by 43 and 36xa0°C. Its char yield at 800xa0°C was increased by about 9.1%. Cured MPR has been characterized by FTIR, XPS, XRD and Raman spectra to discuss the chemical state changes of silicon during pyrolysis process, as well as the effect of silicon on the char yield. On the one hand, the formation of Si–O–C structure can reduce the number of phenyl hydroxyl groups, which contributes to the reduced weight loss. On the other hand, the results indicate that Si–Ox structure was formed from the oxidation of Si–CH3 and hydrolysis of Si–O–C structures. According to Raman analyses, introducing silicone into the system cannot help to promote the formation of a more ordered structure. Additionally, the mechanical properties of cured MPR have also been improved.

Effects of the core of liquid-like SiO2 nanoparticle organic hybrid materials on CO2 capture

A series of specific liquid-like silicon dioxide (SiO2) nanoparticle organic hybrid materials (NOHMs) were successfully prepared by employing different contents of SiO2 as the core, 3-glycidoxypropyl trime thoxysilane (KH-560) or 3-(trihydroxysilyl)-1-propane sulfonic acid (SIT) as the corona and polyetheramine M-1000 (M-1000) as the canopy. These materials showed a solvent-free and liquid-like state at room temperature. The effect of the SiO2 content in the NOHMs with different bonding types on the CO2 capture capacity was investigated at 298xa0K and CO2 pressures ranging from 1.0 to 2.5xa0MPa. It was demonstrated that the capacity of the sorbents improved with the decreasing of SiO2 content. This result was due to the larger number of reactive groups and lower viscosity of the NOHMs. The reactive groups, such as secondary amine and ether groups, react with CO2 molecules, while the lower viscosity creates larger molecular gap and weaker intermolecular forces, which facilitates the penetration of CO2 molecules into the potential space between organic chains. In addition, the NOHMs synthesized via covalent bonds had a much better CO2 capture capacity than the NOHMs with ionic bonds and the same content of SiO2, owing to the protonation of the amine groups in the ionic bond-typed NOHMs, which renders them inactive for CO2 uptake.

Environmental effects on the ionic conductivity of poly(methyl methacrylate) (PMMA)-based quasi-solid-state electrolyte

AbstractQuasi-solid-state dye-sensitized solar cells (QS-DSSCs) using polymer electrolytes display excellent long-term stability with comparable light to electricity conversion efficiency (PCE). In this paper, poly(methyl methacrylate) (PMMA) is chosen as the template polymer, and polymer viscosity and its weight percentage of PMMA in the I3−/I− electrolyte system are optimized considering the competitive factors of the ionic conductivity (σ) and gel dimension stability. A systematic study is carried out to study the environmental factors on the ionic conductivity of quasi-solid electrolytes in terms of storage time, thermal stress, and light soaking. In the different temperature range, the polymer presents different aggregation states and molecular motion forms, which results in different conductive mechanism of the gel electrolyte. It could be described by the Arrhenius equation in the sol state and the Vogel–Tammann–Fulcher (VFT) equation on the gel state, respectively. Both the cyclic voltammetry curve and the Tafel polarization curve indicate that the quasi-solid electrolyte exhibits a lower ion diffusion and transport capacity (1.83u2009×u200910−6xa0cm2/s) than that of thexa0liquid electrolyte (9.15u2009×u200910−6xa0cm2/s). This work provides new insights about the degradation mechanism of polymer electrolytes for QS-DSSC application.n Graphical abstract

OCTAHEDRON SHAPED LEAD SULFIDE NANOCRYSTALS AS COUNTER ELECTRODES FOR QUANTUM DOT SENSITIZED SOLAR CELLS

PbS nanocrystals with octahedron shape are synthesized by a low temperature approach with presence of cation/anion surfactants in aqueous solution. CdS quantum dot sensitized solar cells (QDSSCs) b...