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The fabrication of perovskite solar cells in ambient air is of significant economic benefit. However, to date, there is no satisfactory solution to achieve this, and the reported results of solar cells fabricated in ambient air vary significantly. It has been observed through studies of the “turbid point”, a time point at which the appearance of the precursor film changes from transparent to turbid, that the crystallization of methylammonium lead iodide (MAPbI3) precursor films is strongly affected by humidity. A theoretical model based on the dependence of crystallization on evaporation was developed. We further designed a “humidity-insensitive antisolvent method” based on the turbid point and its tuning to control the fabrication of high-quality MAPbI3 films and solar cells irrespective of the ambient humidity levels. Note that a champion device prepared in ambient air at 90% RH exhibits the efficiency of 19.5%, which is highest among those of the devices prepared in ambient air with over 30% RH. Our study may also impact other perovskite devices and inspire other researchers to perform innovative experiments.

The research for highly selective catalytic transfer hydrogenation (CTH) of 5-hydroxymethylfurfural (5-HMF) into 2,5-bis(hydroxymethyl)furan (BHMF) is an extremely important pathway for biomass valorization. Herein, we use lignosulfonate, a waste by-product from the paper industry, as a building block to coordinate with different metal ions (Hf4+, Zr4+, Fe3+, Al3+, Zn2+) and thus a series of inorganic-biopolymer hybrids (M–LigS) were prepared by a hydrothermal self-assembly method. The resulting Hf–LigS hybrid with strong Lewis acid–base couple sites and moderate Bronsted acidic sites from the inherent sulfonic groups in LigS exhibited the best catalytic activity for CTH of 5-HMF with 2-propanol (2-PrOH) in high yields (90%) under mild reaction conditions (100 °C in 2 h). This robust bifunctional acid–base Hf–LigS is also demonstrated to be effective in one-step reductive etherification of 5-HMF to 5-[(1-methylethoxy)methyl]-2-furanmethanol (MEFA), a potential biomass-derived fuel additive, with 95% yield. Kinetic studies revealed that the activation energy for CTH of 5-HMF was 62.25 kJ mol−1, accounting for the high reaction rate. Isotopic labelling experiments demonstrated that intermolecular hydrogen transfer from the α-C of 2-PrOH to the α-C of 5-HMF was the dominant reaction pathway and the direct hydride transfer on acid–base sites was the rate-determining step. Due to the strong interactions between Hf4+ and phenolic hydroxyl groups, Hf–LigS was highly stable and could be reused without a significant decline in activity.

Exploring both high-performance catalytic materials from non-edible lignocellulosic biomass and selective hydrodeoxygenation of bioderived molecules will enable value-added utilization of renewable feedstocks to replace rapidly diminishing fossil resources. Herein, we developed a scale-up and sustainable method to fabricate gram-quantities of highly dispersed cobalt nanocatalysts sheathed in multilayered N-doped graphene (Co@NG) by using a biomacromolecule carboxymethyl cellulose (CMC) as a raw material. The ionic gelation of CMC, urea and Co2+ ions leads to uniform dispersion and chelation of different species, consequently resulting in the formation of highly distributed Co nanoparticles (NPs) (10.91 nm) with N-enriched graphene shells in the solid-state thermolysis process. The usage of urea as a non-corrosive activation agent can introduce a porous belt-like nanostructure and abundant doped nitrogen. Among all the prepared catalysts in this work, the optimized Co@NG-6 with the largest specific surface area (627 m2 g−1), the most and strongest basic sites, and the highest proportion of pyridinic-N (37.6%) and mesopores exhibited excellent catalytic activity (99% yield of 2-methoxy-p-cresol) for base-free transfer hydrodeoxygenation (THD) of vanillin using bioderived formic acid (FA) as a H source at 160 °C for 6 h. The poisoning tests and electron paramagnetic resonance (EPR) spectra verified that the strong interaction between N atoms and encapsulated Co NPs provided synergistic effects, which were essential for the outstanding catalytic performance of Co@NG-6. The deuterium kinetic isotope effect study clearly demonstrated that the formation of Co-H−via β-hydride elimination and protonation was the rate-determining step, and protic N–H+ and hydridic Co-H− were considered to be active intermediate species in the THD reaction. Furthermore, Co@NG-6 was highly stable for recycling owing to the graphene shells preventing Co NPs from corrosion and aggregation.

The environmental instability of perovskite solar cells caused by the ultraviolet photocatalytic effect of metal oxide layers is a critical issue that must be solved. In this paper, we report improved environmental stability of ZnO film-based planar heterojunction perovskite solar cells, by suppressing photocatalytic activities induced by the ZnO electron transfer layer. The photovoltaic performance and stability in an ambient environment under continuous illumination are effectively improved by applying an aluminum oxide interlayer on the ZnO film to suppress the photocatalytic degradation of perovskites. The highest efficiency of solar cells has increased from 14.62% to 17.17%, and after 250 h of continuous exposure under full spectrum simulated sunlight in air, the efficiency remains as high as 15.03%. The results suggest that effective suppression of photocatalytic degradation of perovskites with a modified electron transfer layer is a new solution to improve the long-term environmental stability of perovskite solar cells.

Oxygen vacancies in non-stoichiometric TiO2 electron transport layers can capture injected electrons and act as recombination centers. In this study, the compact TiO2 electron transport layers of perovskite solar cells (PSCs) are doped with different molar ratios of Fe3+ in order to passivate such defects and improve their electron transport properties. The electrical conductivity, absorption, crystal structure, and the performance of the PSCs are systematically studied. It shows that Fe3+-doping improves the conductivity of TiO2 compact layers compared with the pristine TiO2, boosting the photovoltaic performance of PSCs. The reduced trap-filled limit voltage (VTFL) of the Fe3+-doped TiO2 compact layers suggests that trap density in the Fe3+-TiO2 films is much lower than that of a pristine TiO2 film. With the optimized doping concentration (1 mol%) of Fe3+, the best power conversion efficiency of PSCs is improved from 16.02% to 18.60%.

While most work carried out to date has focused on the solvent annealing of perovskite, in the present work, we focused on the solvent annealing of lead iodide. Based on the two-step spin-coating method, we designed a screening method to search for an effective solvent annealing process for PbI2. PbI2 films were annealed in diverse solvent atmospheres, including DMF, DMSO, acetone, and isopropanol (IPA). We found that the solvent annealing of PbI2 in the DMF, acetone, and IPA atmospheres resulted in dense PbI2 films, which impeded the complete conversion of PbI2 to CH3NH3PbI3. Surprisingly, employing the DMSO solvent annealing process for PbI2 led to porous PbI2, which facilitated the complete conversion of PbI2 to perovskite with larger grain sizes. Solar cells fabricated using the DMSO solvent annealing process exhibited the best efficiency of 18.5%, with a fill factor of 76.5%. This unique solvent annealing method presents a new way of controlling the perovskite film quality for highly efficient solar cells.

Correction for ‘Steering the crystallization of perovskites for high-performance solar cells in ambient air’ by Feng Wang et al., J. Mater. Chem. A, 2019, 7, 12166–12175, DOI: 10.1039/C9TA02566A.

Electronics on flexible and transparent substrates have received muchinterest duetotheirnew functionalitiesand high-speedroll-toroll manufacturing processes. The properties of substrates are crucial, including flexibility, surface roughness, optical transmittance, mechanical strength, maximum processing temperature, etc. Although plastic substrates have been used widely in flexible macroelectronics, there is still a need for next-generation sustainable, high-performance substrates which are thermally stable with tunable optical properties and a higher handling temperature. In this communication, we focus on cellulose-based transparent, biodegradablesubstrates incorporatingeither nanopaperora regenerated cellulose film (RCF). We found that both their optical and mechanical properties are dramatically different due to the difference of their buildingblocks. Highly flexibleorganic-light-emitting diodes (OLEDs) are also demonstrated on the biodegradable substrates, paving the way for next-generation green and flexible electronics.