Youfeng Yue

Efficient and stable large-area perovskite solar cells with inorganic charge extraction layers

Perovskites go large Solar cells made of planar organic-inorganic perovskites now have reported efficiencies exceeding 20%. However, these values have been determined from small illuminated areas. Chen et al. used highly doped inorganic charge extraction layers to make solar cells on the 1 cm2 scale (see the Perspective by Sessolo and Bolink). The layers helped to protect the active layer from degradation by air. The cells achieved governmentlab–certified efficiencies of >15%. Furthermore, 90% of the efficiency was maintained after 1000 hours of operation. Science, this issue p. 944; see also p. 917 Highly doped inorganic layers both improve charge extraction and help protect the active layer from humid air. [Also see Perspective by Sessolo and Bolink] The recent dramatic rise in power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) has triggered intense research worldwide. However, high PCE values have often been reached with poor stability at an illuminated area of typically less than 0.1 square centimeter. We used heavily doped inorganic charge extraction layers in planar PSCs to achieve very rapid carrier extraction, even with 10- to 20-nanometer-thick layers, avoiding pinholes and eliminating local structural defects over large areas. The robust inorganic nature of the layers allowed for the fabrication of PSCs with an aperture area >1 square centimeter that have a PCE >15%, as certified by an accredited photovoltaic calibration laboratory. Hysteresis in the current-voltage characteristics was eliminated; the PSCs were stable, with >90% of the initial PCE remaining after 1000 hours of light soaking.

Mechano-actuated ultrafast full-colour switching in layered photonic hydrogels

Photonic crystals with tunability in the visible region are of great interest for controlling light diffraction. Mechanochromic photonic materials are periodically structured soft materials designed with a photonic stop-band that can be tuned by mechanical forces to reflect specific colours. Soft photonic materials with broad colour tunability and fast colour switching are invaluable for application. Here we report a novel mechano-actuated, soft photonic hydrogel that has an ultrafast-response time, full-colour tunable range, high spatial resolution and can be actuated by a very small compressive stress. In addition, the material has excellent mechanical stability and the colour can be reversibly switched at high frequency more than 10,000 times without degradation. This material can be used in optical devices, such as full-colour display and sensors to visualize the time evolution of complicated stress/strain fields, for example, generated during the motion of biological cells.

High‐Quality Mixed‐Organic‐Cation Perovskites from a Phase‐Pure Non‐stoichiometric Intermediate (FAI)1−x‐PbI2 for Solar Cells

A high-quality mixed-organic-cation perovskite (MA)x (FA)1- x PbI3 is prepared from a phase-pure non-stoichiometric intermediate complex (FAI)1- x -PbI2 . The phase-pure (FAI)1- x -PbI2 probably facilitates homogenous nucleation and modulates the growth kinetics during the crystallization of (MA)x (FA)1- x PbI3 . This strategy can be expected to pave the way for the development of mixed-organic-cation perovskite solar cells.

Enhanced Stability of Perovskite Solar Cells through Corrosion‐Free Pyridine Derivatives in Hole‐Transporting Materials

The molecular structure of pyridine derivatives is critical to perovskite solar cell performance, especially stability. Most of the pyridine additives easily form complexes with perovskite. A new pyridine additive with a long alkyl chain substituted at its o-position does not corrode perovskite. The stability of devices containing this additive is the highest among the investigated cells.

Consecutive Morphology Controlling Operations for Highly Reproducible Mesostructured Perovskite Solar Cells.

Perovskite solar cells have shown high photovoltaic performance but suffer from low reproducibility, which is mainly caused by low uniformity of the active perovskite layer in the devices. The nonuniform perovskites further limit the fabrication of large size solar cells. In this work, we control the morphology of CH3NH3PbI3 on a mesoporous TiO2 substrate by employing consecutive antisolvent dripping and solvent-vapor fumigation during spin coating of the precursor solution. The solvent-vapor treatment is found to enhance the perovskite pore filling and increase the uniformity of CH3NH3PbI3 in the porous scaffold layer but slightly decrease the uniformity of the perovskite capping layer. An additional antisolvent dripping is employed to recover the uniform perovskite capping layer. Such consecutive morphology controlling operations lead to highly uniform perovskite in both porous and capping layers. By using the optimized perovskite deposition procedure, the reproducibility of mesostructured solar cells was greatly improved such that a total of 40 devices showed an average efficiency of 15.3% with a very small standard deviation of 0.32. Moreover, a high efficiency of 14.9% was achieved on a large-size cell with a working area of 1.02 cm(2).

Surface functionalization of high free-volume polymers as a route to efficient hydrogen separation membranes

There is a sparcity of polymeric membranes with sufficient selectivity for efficient hydrogen separation from syn-gas products, primarily carbon dioxide. Despite hydrogens significantly smaller kinetic diameter, low selectivity arises as other gases are generally more condensable within typical polymeric membranes. Here we report an in situ-controllable, surface polymerization of polydopamine (PDA) and polyaniline (PANI) on high free-volume glassy polymer films, specifically the well studied polymer of intrinsic microporosity (PIM-1) and poly(1-trimethylsilyl-1-propyne) (PTMSP). The resulting nanolayer composite membranes demonstrate a remarkable hydrogen selectivity against N2, CH4 and CO2 (H2/CO2 ∼ 50). The PDA or PANI layers principally serve to increase the diffusive selectivity towards hydrogen whilst the high free volume supports of PIM-1 or PTMSP provide a highly permeable interface for defect-free growth of the selective layer. Whilst both PANI and PDA are effective, these selective layers were found to grow by heterogeneous or homogeneous modes respectively.

Selective Deposition of Insulating Metal Oxide in Perovskite Solar Cells with Enhanced Device Performance

We report a simple methodology for the selective deposition of an insulating layer on the nanoparticulate TiO2 (np-TiO2) mesoporous layer of perovskite solar cells. The deposited MgO insulating layer mainly covered the bottom part of the np-TiO2 layer with less coverage at the top. The so-called quasi-top-open structure is introduced to act as an efficient hole-blocking layer to prevent charge recombination at the physical contact of the transparent conducting oxide with the perovskite. This leads to an open-circuit voltage higher than that of the reference cell with a compact TiO2 hole-blocking layer. Moreover, such a quasi-top-open structure can facilitate the electron injection from perovskite into the np-TiO2 mesoporous layer and improve the spectral response at longer wavelength because of the less covered insulating layer at the top. This work provides an alternative way to fabricate perovskite solar cells without the need to use a conventional compact TiO2 layer.

Synthesis of a Novel Ligand Containing Phenyl Pyridine

In this article, we provide a new, efficient route to synthesize 2-[3-(3,4-bis(2-ethylhexyloxy)phenyl]phenyl pyridine ligand from readily available starting materials. The target compound was obtained by a condensation reaction and Suzuki coupling reaction. Structures of compounds were demonstrated by 1H NMR, 13C NMR, and high-resolution mass spectrometry. The advantages of this synthetic route are simple operation, mild reaction conditions, and good yields.

Self-Assembled Liquid-Crystalline Membranes Form Supramolecular Hydrogels via Hydrogen Bonding

Developing simple methods to organize nanoscale building blocks into ordered superstructures is a crucial step toward the practical development of nanotechnology. Bottom-up nanotechnology using self-assembly bridges the molecular and macroscopic, and can provide unique material properties, different from the isotropic characteristics of common substances. In this study, a new class of supramolecular hydrogels comprising 40 nm thick linear polymer layers sandwiched between nanolayers of self-assembled amphiphilic molecules are prepared and studied by nuclear magnetic resonance spectroscopy, scanning electronic microscopy, small angle X-ray diffraction, and rheometry. The amphiphilic molecules spontaneously self-assemble into bilayer membranes when they are in liquid-crystal state. The hydrogen bonds at the interface of the nanolayers and linear polymers serve as junctions to stabilize the network. These hydrogels with layered structure are facile to prepare, mechanically stable, and with unique temperature-dependent optical transparency, which makes it interesting in applications, such as soft biological membranes, drug release, and optical filters.

Synthesis, characterisation and photophysical properties of α,β-diaryl-acrylonitrile derivatives

α,β-Diarylacrylonitrile derivatives can be prepared by two different routes: (1) the intermolecular condensation of the same arylacetonitriles (2) the condensation of arylaldehydes and arylacetonitriles with a catalytic amount of NaOCH3 at room temperature. Several α,β-diarylacrylonitrile derivatives have been synthesised in this paper and characterised. The UV-vis absorption and photoluminescent (PL) spectra of the products were investigated.