Obtaining both high open-circuit voltage (Voc) and short-circuit current density (Jsc) has been a major challenge for efficient all-polymer solar cells (all-PSCs). Herein, we developed a polymer acceptor PF5-Y5 with...

We herein report a new class of photonic crystals with hierarchical structures, which are of color tunability over pH. The materials were fabricated through the deposition of polymethylacrylic acid (PMAA) onto a Morpho butterfly wing template by using a surface bonding and polymerization route. The amine groups of chitosan in Morpho butterfly wings provide reaction sites for the MAA monomer, resulting in hydrogen bonding between the template and MAA. Subsequent polymerization results in PMAA layers coating homogenously on the hierarchical photonic structures of the biotemplate. The pH-induced color change was detected by reflectance spectra as well as optical observation. A distinct U transition with pH was observed, demonstrating PMAA content-dependent properties. The appearance of the unique U transition results from electrostatic interaction between the -NH3(+) of chitosan and the -COO(-) groups of PMAA formed, leading to a special blue-shifted point at the pH value of the U transition, and the ionization of the two functional groups in the alkali and acid environment separately, resulting in a red shift. This work sets up a strategy for the design and fabrication of tunable photonic crystals with hierarchical structures, which provides a route for combining functional polymers with biotemplates for wide potential use in many fields.

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A simple synthesis method combining a sol‐gel route followed by a reduction step is developed for the fabrication of magnetophotonic crystal (MPC) materials from Morpho butterfly wings. The sol‐gel route leads to hematite with a photonic crystal structure (PC‐α‐Fe2O3) being faithfully replicated from a biotemplate, and the desired magnetophotonic crystal Fe3O4 (MPC‐Fe3O4) is obtained by the reduction of the PC‐α‐Fe2O3 under a H2/Ar atmosphere. The structural replication fidelity of the process is demonstrated on both the macro‐ and microscale, and even down to the nanoscale, as evidenced by scanning electron microscopy, X‐ray diffraction, reflectance measurements, and transmission electron microscopy. It is found that the chemical transformation of PC‐α‐Fe2O3 to MPC‐Fe3O4 changes only the dielectric constant and does not induce structural defects that could affect the photonic‐crystal properties of the composite. The photonic band gap of MPC‐Fe3O4 can be red‐shifted with an increase of the external magnetic field strength, which is further supported by theoretical calculations. The reported biomimetic technique provides an effective approach to produce magnetophotonic crystals from nature with 3D networks, which may open up an avenue for the creation of new magneto‐optical devices and theoretical research in this field.

A novel strategy is proposed to construct simple-structured SMAs using a weakly electron-deficient thiazolothiazole (TTz) core. The highest PCE of 8.77% is recorded for TTz1-based OSCs, which is the highest efficiency to date among non-fullerene OSCs with simple-structured SMAs.

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During the past five years, polymer solar cells (PSCs) based on narrow bandgap (NBG) fused-ring small molecule (SM) acceptors have made considerable progress, [1][2][3][4] among which the state-of-the-art PSCs have achieved power conversion efficiencies (PCEs) of 16-18%. [5][6][7][8][9][10][11][12][13][14][15][16][17] Regarding such SM acceptor-based PSCs, the all-polymer solar cells (all-PSCs) consisting of a polymer donor and a polymer acceptor show unique advantages in the flexible large-scale and wearable energy generators due to their excellent morphology stability and mechanical robustness. [18][19][20][21] However, most of the efficient all-PSCs have PCEs ranging in 8-10%, [22][23][24][25][26][27][28][29][30][31][32][33][34] although a few of them achieved PCEs over 11%, [35][36][37] which is still far behind that of the efficient PSCs based on SM acceptors due to the lack of high-performance polymer acceptors. To date, polymer acceptors have been mainly confined into a small number of structural building blocks, [24][25][26][38][39][40] and the most widely studied one is the polymer N2200 with a donor-acceptor (D-A) backbone of naphthalene diimide (NDI)-alt-bithiophene due to its NBG and suitable molecular energy levels. [39][40][41][42][43] However, N2200 neat film suffers from a low absorption coefficient of %0.3 Â 10 5 cm À1 and an excess strong crystallinity and stacking, which usually lead to the limited photocurrent and large phase separation in active layers. [39][40][41][42][43] The limited light absorption capacity for most polymer acceptors hinders the improvement of the power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs). Herein, by simultaneously increasing the conjugation of the acceptor unit and enhancing the electron-donating ability of the donor unit, a novel narrowbandgap polymer acceptor PF3-DTCO based on an A-D-A-structured acceptor unit ITIC16 and a carbon-oxygen (C-O)-bridged donor unit DTCO is developed. The extended conjugation of the acceptor units from IDIC16 to ITIC16 results in a red-shifted absorption spectrum and improved absorption coefficient without significant reduction of the lowest unoccupied molecular orbital energy level. Moreover, in addition to further broadening the absorption spectrum by the enhanced intramolecular charge transfer effect, the introduction of C-O bridges into the donor unit improves the absorption coefficient and electron mobility, as well as optimizes the morphology and molecular order of active layers. As a result, the PF3-DTCO achieves a higher PCE of 10.13% with a higher short-circuit current density ( J sc ) of 15.75 mA cm À2 in all-PSCs compared with its original polymer acceptor PF2-DTC (PCE ¼ 8.95% and J sc ¼ 13.82 mA cm À2 ). Herein, a promising method is provided to construct high-performance polymer acceptors with excellent optical absorption for efficient all-PSCs.