Solution-processable small molecules for organic solar cells have attracted intense attention for their advantages of definite molecular structures compared with their polymer counterparts. However, the device efficiencies based on small molecules are still lower than those of polymers, especially for inverted devices, the highest efficiency of which is <9%. Here we report three novel solution-processable small molecules, which contain π-bridges with gradient-decreased electron density and end acceptors substituted with various fluorine atoms (0F, 1F and 2F, respectively). Fluorination leads to an optimal active layer morphology, including an enhanced domain purity, the formation of hierarchical domain size and a directional vertical phase gradation. The optimal morphology balances charge separation and transfer, and facilitates charge collection. As a consequence, fluorinated molecules exhibit excellent inverted device performance, and an average power conversion efficiency of 11.08% is achieved for a two-fluorine atom substituted molecule.

The high efficiency all-small-molecule organic solar cells (OSCs) normally require optimized morphology in their bulk heterojunction active layers. Herein, a small-molecule donor is designed and synthesized, and single-crystal structural analyses reveal its explicit molecular planarity and compact intermolecular packing. A promising narrow bandgap small-molecule with absorption edge of more than 930 nm along with our home-designed small molecule is selected as electron acceptors. To the best of our knowledge, the binary all-small-molecule OSCs achieve the highest efficiency of 14.34% by optimizing their hierarchical morphologies, in which the donor or acceptor rich domains with size up to ca. 70 nm, and the donor crystals of tens of nanometers, together with the donor-acceptor blending, are proved coexisting in the hierarchical large domain. All-small-molecule photovoltaic system shows its promising for high performance OSCs, and our study is likely to lead to insights in relations between bulk heterojunction structure and photovoltaic performance.

A ternary blend system with two donors and one acceptor provides an effective route to improve the performance of organic solar cells. A synergistic effect of polymer and small molecules is observed in ternary solar cells, and the power conversion efficiency (PCE) of the ternary system (8.40%) is higher than those of binary systems based on small molecules (7.48%) or polymers (6.85%).

Two new star-shaped D-π-A molecules with triphenylamine (TPA) as core and donor unit, dicyanovinyl (DCN) as end group and acceptor unit, and 4,4 0 -dihexyl-2,2 0 -bithiophene (bT) or 4, 4 0 -dihexyl-2,2 0 -bithiophene vinylene (bTV) as π bridge, S(TPA-bT-DCN) and S(TPA-bTV-DCN), were synthesized for the application as donor materials in solution-processed bulk-heterojunction organic solar cells (OSCs). The two compounds are soluble in common organic solvents, because of the three-dimensional structure of the TPA unit and the two hexyl side chains on the bithiophene unit. S(TPA-bTV-DCN) film shows a broad absorption band from 360 to 750 nm. Absorption edge of S(TPA-bTV-DCN) film is red-shifted by ca. 78 nm than that of S(TPA-bT-DCN) film, benefitted from the vinylene bridges between TPA and bithiophene units in S(TPA-bTV-DCN). Power conversion efficiency (PCE) of the solution-processed bulk-heterojunction OSC based on a blend of S(TPA-bTV-DCN) and [6,6]-phenyl-C 71 -butyric acid methyl ester (1:2, w/w) reached 3.0% with a short circuit current density of 7.76 mA/cm 2 and an open circuit voltage of 0.88 V, under the illumination of AM.1.5, 100 mW/cm 2 . In comparison, PCE of the OSC based on S(TPA-bT-DCN) as donor is 1.4% under the same experimental conditions. The PCE of 3.0% for S(TPA-bTV-DCN) is among the top values for the solution-processed molecule-based OSCs reported so far.

to potentially obtain champion PCE with thermally stable morphology in ASM-OSCs.

crystalline small molecules as donor materials. [8][9][10][11][12] Compared with polymers, crystallinity is more critical for small molecules because of their much lower molecular weight leading to ineffi cient charge extraction and poorer morphology. [ 13 ] Other than traditional 3D amorphous triphenylamine (TPA) non-planar molecules, [ 3,5,14,15 ] crystalline small molecules exhibit much better hole mobilities and morphologies, and the highest PCE is enhanced from 4.76% to 8.12%. [ 11,16 ] Under the premise of proper miscibility with 6,6-phenyl-C 61 /C 71butyric acid methyl ester (PCBM), crystalline small molecules possess the planarity of conjugated backbones to strengthen π−π stacking and thus can self-assemble into ordered domains with close intermolecular stacking to obtain good device performance. [ 13,[17][18][19] To further optimize the design of crystalline small molecules, adjusting the alkyl chain length is an effective method for modulating molecular packing according to the extensive study of the polymers; [20][21][22][23] however, this approach has not been attracting adequate attention in small molecules.Several recent works on small molecules demonstrate the remarkable effects of different alkyl chain lengths on the morphology and performance of the resulting devices. [ 16,[24][25][26] For example, Nguyen et al. changed the alkyl chains linked to the middle diketopyrrolopyrrole (DPP) unit and found that subtle changes alter the tendency for crystallization of molecules and device performance. [ 26 ] Min et al. varied the chains linked to the acceptor of star-shaped molecules with dodecyl, hexyl, ethyl, and methyl groups; the results of the authors implied that small changes exert signifi cant effects on morphology, and the PCE of the resulting device increased from 2.87% to 4.86% as the alkyl chain lengths decreased. [ 16 ] Therefore, accurate design and shortening of alkyl chains based on a planar-conjugated backbone could effi ciently advance morphologies in the solid state and ultimately improve device performance.In the current study, we designed and synthesized two solution-processable small molecules DOO3OTTBDT ( M 1 ) and DOP3HTTBDT ( M 2 ) ( Scheme 1 ) based on a conjugated backbone with ethylhexyl-thiophene substituted benzodithiophene (TBDT) as core and trithiophene as π-bridge and end-capped with a novel acceptor unit (oxo-alkylated nitrile), with octyl and hexyl chains that were attached to the π-bridge, and octyl and pentyl

Most state-of-the-art scene text detection algorithms are deep learning based methods that depend on bounding box regression and perform at least two kinds of predictions: text/non-text classification and location regression. Regression plays a key role in the acquisition of bounding boxes in these methods, but it is not indispensable because text/non-text prediction can also be considered as a kind of semantic segmentation that contains full location information in itself. However, text instances in scene images often lie very close to each other, making them very difficult to separate via semantic segmentation. Therefore, instance segmentation is needed to address this problem. In this paper, PixelLink, a novel scene text detection algorithm based on instance segmentation, is proposed. Text instances are first segmented out by linking pixels within the same instance together. Text bounding boxes are then extracted directly from the segmentation result without location regression. Experiments show that, compared with regression-based methods, PixelLink can achieve better or comparable performance on several benchmarks, while requiring many fewer training iterations and less training data.

A novel “N‐ π ‐N” type oligomeric acceptor of 2BTP‐2F‐T, constructed by two small non‐fullerene acceptor (NFA) units linked with a thiophene π bridge is reported. The 2BTP‐2F‐T not only combines the advantages of small NFA and polymeric acceptors (PYF‐T‐ o ) with similar units but also exhibits superior characteristics of high absorption coefficient and high electron moblity( µ e) ) with less dependence on molecular packing. Using PM6 as the donor, a remarkable efficiency of 18.19% is obtained with an open circuit ( V oc ) of 0.911 V, short current circuit ( J sc ) of 25.50 mA cm −2 , and fill factor (FF) of 78.3%, which is much better than that of the corresponding monomer (16.54%) and PYF‐T‐ o (15.8%) based devices. The much‐improved efficiency results from two aspects: 1) an enhanced FF due to the largely improved µ e and well‐controlled morphology ; 2) a higher value of ( J sc × V oc ) due to its higher absorption coefficient and efficient charge generation at a similar low energy loss. Furthermore, the PM6/2BTP‐2F‐T device possesses the longest T 80 lifetime to light‐soaking and comparable high thermal stability with PM6/PYF‐T‐ o . The results indicate that the “N‐ π ‐N” type oligomeric acceptor has a great application prospect due to its superior high efficiency and improved stability in organic solar cells.