The development of solar energy can potentially meet the growing requirements for a global energy system beyond fossil fuels, but necessitates new scalable technologies for solar energy storage.

A non-conjugated polymer acceptor PF1-TS4 was firstly synthesized by embedding a thioalkyl segment in the mainchain, which shows excellent photophysical properties on par with a fully conjugated polymer, with a low optical band gap of 1.58 eV and a high absorption coefficient > 10 5 cm À1 , a high LUMO level of À3.89 eV, and suitable crystallinity. Matched with the polymer donor PM6, the PF1-TS4-based all-PSC achieved a power conversion efficiency (PCE) of 8.63 %, which is % 45 % higher than that of a device based on the small molecule acceptor counterpart IDIC16. Moreover, the PF1-TS4-based all-PSC has good thermal stability with % 70 % of its initial PCE retained after being stored at 85 8C for 180 h, while the IDIC16-based device only retained % 50 % of its initial PCE when stored at 85 8C for only 18 h. Our work provides a new strategy to develop efficient polymer acceptor materials by linkage of conjugated units with non-conjugated thioalkyl segments.

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.

Surfactants are used widely to control the synthesis of shaped noble-metal nanoparticles. In this work, a mixture of hexadecyltrimethylammonium bromide (CTAB), a cationic surfactant; sodium oleate (NaOL), an anionic surfactant; palladium chloride; and a reducing agent were used in the seed-mediated synthesis of palladium nanoparticles. By controlling the surfactant mixture ratio, we initially discovered that palladium nanodendrites with narrow size distribution were formed instead of the traditional nanocubes, synthesized with only CTAB. In order to investigate the optimal ratio to produce Pd nanodendrites with a high yield and narrow size distribution, samples synthesized with multiple molar ratios of the two surfactants were prepared and studied by transmission electron microscopy, dynamic light scattering, conductance, and ultraviolet−visible spectroscopy. We propose that the addition of NaOL alters the arrangement of surfactants on the Pd seed surface, leading to a new pattern of growth and aggregation. By studying the nanodendrite growth over time, we identified the reduction period of Pd 2+ ions and the formation period of the nanodendrites. Our further experiments, including the replacement of CTAB with hexadecyltrimethylammonium chloride (CTAC) and the replacement of NaOL with sodium stearate, showed that CTA + ions in CTAB and OL − ions in NaOL play the main roles in the formation of nanodendrites. The formation of palladium nanodendrites was robust and achieved with a range of temperatures, pH and mixing speeds.

A non-conjugated polymer acceptor PF1-TS4 was firstly synthesized by embedding a thioalkyl segment in the mainchain, which shows excellent photophysical properties on par with a fully conjugated polymer, with a low optical band gap of 1.58 eV and a high absorption coefficient > 10 5 cm À1 , a high LUMO level of À3.89 eV, and suitable crystallinity. Matched with the polymer donor PM6, the PF1-TS4-based all-PSC achieved a power conversion efficiency (PCE) of 8.63 %, which is % 45 % higher than that of a device based on the small molecule acceptor counterpart IDIC16. Moreover, the PF1-TS4-based all-PSC has good thermal stability with % 70 % of its initial PCE retained after being stored at 85 8C for 180 h, while the IDIC16-based device only retained % 50 % of its initial PCE when stored at 85 8C for only 18 h. Our work provides a new strategy to develop efficient polymer acceptor materials by linkage of conjugated units with non-conjugated thioalkyl segments.