Super-sensitive and ultra-selective detection of explosives plays a crucial role in anti-terrorism operations, homeland security, civilian safety and environment protection. Among the developed fluorescent probes, the polymers with aggregation-induced emission (AIE) characteristics have drawn much attention due to their bright emission in the aggregate and solid states. However, no review has summarized the development of AIE-active polymers for explosive detection. Herein, we reviewed the recent progress on using AIE-active polymers to detect explosives with super-amplification quenching effect. Moreover, the challenges and opportunities in this area were also briefly discussed.

Molecular bulks are favorable for the thermal and morphological stability in organic wide-bandgap semiconducting polymers with potential applications in both information and energy electronics. In this review, we present our progress in the design of fluorene-based bulky semiconductors with a fractal four-element pattern. Firstly, we established one-pot methods to spirofluorenes, especially spiro[fluorene-9, 9'-xanthene] (SFX) serving as the next-generation spiro-based semiconductors. Secondly, we observed the supramolecular forces at the bulky groups and discovered the supramolecular steric hindrance (SSH) effect on polymorphisms, nanocrystals as well as device performance. Thus, a synergistically molecular attractor-repulsor theory (SMART) was proposed for the control of nanocrystal morphology, thin film phase and morphology. Thirdly, the third possible type of defects has been identified to generate green band (g-band) emission in wide-bandgap semiconductors by the introduction of molecular strain design of cyclofluorene. Finally, the first bulky polydiarylfluorene with highly crystalline and β conformation was achieved by an attractor-repulsor design of tadpole-shape monomer, which offered an effective platform to fabricate stable wide-bandgap semiconducting devices. All the discoveries offer the solid basis to break through bottlenecks of organic/polymer wide-bandgap semiconductors by the improvements of overall performances.

Development of organic semiconductors is one of the most intriguing and productive topics in material science and engineering. Many efforts have been made on the synthesis of aromatic building blocks such as benzene, thiophene and pyrrole due to the facile preparation accompanied by the intrinsic environmental stability and relatively efficient properties of the resulting polymers. In the past, furan has been less explored in this field because of its high oxidation potential. Recently, furan has attracted obsession due to its weaker aromaticity, the greater solubilities of furan-containing π-conjugated polymers relative to other benzenoid systems and the accessibility of furan-based starting materials from renewable resources. This review elaborates the advancements of organic photovoltaic polymers containing furan building blocks. The uniqueness and advantages of furan-containing building blocks in semiconducting materials are also discussed.

Ternary organic solar cells have drawn great attention because the highest power conversion efficiencies have reached~12%, showing a promising prospect for the future applications. However, most reported ternary solar cells focus on the increase of light absorption and the optimization of energy alignment, but ignore the importance of morphology. Herein, we summarize the morphology optimization on the ternary blends with different structural aspects, such as controlling crystallinity, crystal orientation, domain size, and domain purity. Furthermore, the fundamental mechanism of ternary solar cells which is related to the morphology has been described. The efforts here will provide a guiding role for the morphology optimization on the ternary solar cells in the future.

B←N coordination bond can be used to develop polymer electron acceptors for efficient all-polymer solar cells (all-PSCs). Here, we report a new alternating conjugated polymer containing two building blocks based on B←N unit. The polymer exhibits strong light absorption in the visible range, low-lying LUMO/HOMO energy levels and moderate electron mobility. The resulting all-PSC devices exhibit power conversion efficiencies of 1.50%-2.47%.

Donor-acceptor (D-A) type fully conjugated block copolymer systems have been rarely reported due to the challenges in synthetic approaches to prepare well-defined low-polydispersity products. In this work, fully conjugated block copolymers are synthesized in a one-pot reaction through Stille coupling polycondensation, by utilizing the end-functional polymer copolymerization method. End-functional P3HT are copolymerized with AA (2, 7-dibromo-9-(heptadecan-9-yl)-9H-carbazole) and BB (4, 7-bis (5-(trimethylstannyl) thiophen-2-yl) benzo[c] [1, 2, 5]thiadiazole, TBT) type monomers, respectively. The orthogonal solubility between the very soluble P3HT donor and the insoluble PCDTBT acceptor block improves the purity of block copolymers as well as distinct nano-scale phase-separation compared with other reports on miscibility of donor and acceptor polymer block. Further purification via preparative GPC is carried out to remove the excess of unreacted P3HT and free PCDTBT as well as to achieve low polydispersity of block copolymers. The chemical structure of the P3HT-b-PCDTBT block copolymers are verified via ¹H-NMR, and further confirmed by FTIR spectra. The block copolymer shows broad absorption and moderate optical band gap of 1.8 eV. Furthermore, the fully conjugated block copolymer films exhibit significant fine structures, much smoother film morphology compared to P3HT/PCDTBT polymer blends. By adding a small amount of block copolymer P3HT-b-PCDTBT as a compatibilizer into the bulk-heterojunction of P3HT:PC₆₁BM blends, polymer solar cells with an 8% increase of short circuit current (J_sc) and 10% increase of power conversion efficiency (PCE) are achieved owing to the improvement of the active-layer film morphology. To the best of our knowledge, this is the first report on donor-acceptor type fully conjugated block copolymer as an effective ternary additive in polymer:fullerene bulk heterojunction solar cells.

A series of conjugated polymers based on PFS derivatives with π-conjugated 5-(9H-fluoren-2-yl)-2, 2'-bithiophene (fluorene-alt-bithiophene) backbones, namely PFS-3C, PFS-4C and PFS-6C, were synthesized for their use as the anode interfacial layers (AILs) in the efficient fullerene-free polymer solar cells (PSCs). Alkyl sulfonate pendants with different lengths of alkyl side chains were introduced in the three polymers in order to investigate the effect of the alkyl chain length on the anode modification. The obtained three polymers exhibited similar absorption bands and energy levels, indicating that changing the length of the alkyl side chains did not affect the optoelectronic properties of the conjugated polymers. Based on the PBDB-T:ITIC active layer, we fabricated the fullerene-free PSCs using the three polymers as the AILs. The superior performance of the fullerene-free PSC device was achieved when PFS-4C was used as the AIL, showing a power conversion efficiency (PCE) of 10.54%. The high performance of the PFS-4C-modified device could be ascribed to the high transmittance, suitable work-function (WF) and smooth surface of PFS-4C. To the best of our knowledge, the PCE obtained in the PFS-4C-modified device is among the highest PCE values in the fullerene-free PSCs at present. These results demonstrate that the PFS derivatives are promising candidates in serving as the AIL materials for high-performance fullerene-free PSCs.

Two polymers containing (E)-2, 3-bis (thiophen-2-yl) acrylonitrile (CNTVT) as a donor unit, perylene diimide (PDI) or naphthalene diimide (NDI) as an acceptor unit, are synthesized by the Stille coupling copolymerization, and used as the electron acceptors in the solution-processed organic solar cells (OSCs). Both polymers exhibit broad absorption in the region of 300-850 nm. The LUMO energy levels of the resulted polymers are ca. -3.93 eV and the HOMO energy levels are -5.97 and -5.83 eV. In the binary blend OSCs with PTB7-Th as a donor, PDI polymer yields the power conversion efficiency (PCE) of up to 1.74%, while NDI polymer yields PCE of up to 3.80%.

Perylene bisimide (PBI) unit has been widely used to design conjugated materials, which can be used as electron acceptor in organic solar cells due to its strong electron-deficient ability. In this work, a conjugated polymer based on PBI dimer as monomer was designed, synthesized, and compared to the conjugated polymer containing single PBI as repeating units. The two conjugated polymers were found to have similar molecular weight, absorption spectra and energy levels. Density functional theory calculation revealed that the PBI dimer-based polymer exhibited highly twisted conjugated backbone due to the large dihedral angle between the two PBI units. The PBI-based polymers as electron acceptor were applied into polymer-polymer solar cells, in which PBI dimer-based polymer solar cells were found to show a high short circuit current density (J_sc=11.2 mA·cm^-2) and a high power conversion efficiency (PCE) of 4.5%. In comparison, the solar cells based on PBI-based polymer acceptor only provided a J_sc of 7.2 mA·cm^-2 and PCE of 2.5%. The significantly enhanced PCE in PBI dimer-based solar cells was attributed to the mixed phase in blended thin films, as revealed by atom force microscopy. This study demonstrates that PBI dimer can be used to design polymer acceptors for high performance polymer-polymer solar cells.

A series of copolymers, based on benzo[1, 2-b:4, 5-b']dithiophene (BDT) as the electron donor and 2, 1, 3-benzothiadiazole (BT)/diketopyrrolo[3, 4-c]pyrrole (DPP) as the electron acceptors, were synthesized for highly efficient polymer solar cells. By changing the BT/DPP ratio in the conjugated backbone, the absorption, energy levels, molecular aggregation and carrier mobility could be finely tuned. With increased DPP content, the absorption range was extended to the longer wavelength region with narrower bandgaps. The highest occupied molecular orbital (HOMO) levels were also raised up and the molecular aggregation was enhanced. The balance of these factors would afford a remarkable device performance enhancement. Polymer P3 with BT:DPP=0.7:0.3 (molar ratio) exhibited the highest power conversion efficiency (PCE) of 9.01%, with open circuit voltage (V_oc)=0.73 V, short current density (J_sc)=18.45 mA·cm^-2, and fill factor (FF)=66.9%. The PCE value was improved by 48.7% compared to P1 and by 117.6% compared to P7, respectively, indicating a great potential in photovoltaic application.

Conventional organic solar cell's (OSC) architectures, including rigid transparent substrate (Glass), conductive electrode (Indium tin oxide, ITO) and small working areas, are widely utilized in organic photovoltaic fields. However, such a structure as well as conventional spin-coating method obviously restrict their industrial application. In this article, we report the deposition of silver nanowires (AgNWs) on the flexible substrate by slot-die printing. The obtained AgNWs films exhibited a high transmittance and a low resistance, and were further used as the transparent conductive electrode of OSCs. A typical conjugated polymer, poly[(2, 5-bis (2-hexyldecyloxy) phenylene)-alt-(5, 6-difluoro-4, 7-di (thiophen-2-yl) benzo[c] [1, 2, 5]thiadiazole)] (PPDT2FBT), was used as the active material to fabricate large-area (7 cm²) solar cells by a slot-die coating process. The power conversion efficiency (PCE) could reach 1.87% initially and further increased to 3.04% by thermal annealing. Compared to the performance of reference cell on ITO substrate, the result indicated that the AgNWs could be developed as an alternative substitute of conductive electrode to fabricate the large-area flexible OSCs by roll-to-roll printing.

We present a microwave-assisted one-pot polymerization with three-components of alkynes, aldehydes and amines for the synthesis of new amino-functionalized optoelectronic polymers. The polymerization of diynes (1a-1c), dialdehydes (2a and 2b) and dibenzylamine catalyzed by InCl₃ was carried out smoothly within 1 h under microwave radiation, yielding four soluble polymers with high molecular weights. The resulting polymers P1 and P2 could be easily dissolved in alcohol and thus utilized as the cathode interlayer for polymer solar cells (PSCs). Compared with the control device, the PSCs with P1 and P2 as the cathode interlayer and PTB7-Th:PC₇₁BM as the photoactive layer exhibited significantly higher power conversion efficiencies (PCEs) of 9.49% and 9.16%, respectively. These results suggest that this polycoupling reaction is an efficient approach to construct three-component polymers for the practical applications.

A polymer (poly (9, 10-anthracenevinylene-alt-4, 4'-(9, 9-bis (4-(4'-(1, 2, 2'-triphenylvinyl) phenoxy) butyl)-9H-fluorene-2, 7-diyl) dibenzaldehyde), P1) was successfully synthesized through the Wittig-Horner reaction by employing fluorene and 9, 10-distyrylanthracene moieties as building blocks for backbone and tetraphenylethenes as pendant groups. Photophysical and thermal properties of the resulting polymeric emitter were fully characterized by ultraviolet-visible (UV-Vis) absorption and photoluminescence (PL) spectra, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). While P1 emits an orange-light centered at 567 nm in dilute tetrahydrofuran (THF) solution, the solid powder of the polymer exhibits strong yellow emission peaked at 541 nm. It is also found that the as-synthesized polymer shows unique property of aggregation-enhanced emission (AEE). In addition, P1 possesses high thermal stability with a decomposition temperature (T_{d, 5%}) of 430℃ and high morphological stability with a glass transition temperature (T_g) of 171℃. Under the stimulus of mechanical force, the emission of P1 can be changed from yellow to red (Δλ_max=61 nm), showing a remarkable mechanochromism. The results from XRD analysis suggest that such mechanochromic phenomenonof P1 is probably caused by the destruction of crystalline structure, which leads to the conformational planarization of the distyrylanthracene moieties forming by the polymerization and the increase of molecular conjugation of the backbone.

Four polymers based on perylenediimide co-polymerized with thiophene, bithiophene, selenophone and thieno[3, 2-b]thiophene were investigated as the acceptor materials in all-polymer solar cells. Two different donor polymers, poly[4, 8-bis (5-(2-ethylhexyl) thiophen-2-yl) benzo[1, 2-b; 4, 5-b']dithiophene-2, 6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3, 4-b]thiophene)-2-carboxylate-2, 6-diyl] (PTB7-Th) and poly[(5, 6-difluoro-2, 1, 3-benzothiadiazol-4, 7-diyl)-alt-(3, 3"'-di (2-dodecyltetradecyl)-2, 2';5', 2";5", 2"'-quaterthiophen-5, 5"'-diyl)] (PffBT4T-2DT), with suitably complementary absorption spectra and energy levels were applied and examined. Among all different donor-acceptor pairs studied here, the combination of PTB7-Th:poly[N,N'-bis (1-hexylheptyl)-3, 4, 9, 10-perylenediimide-1, 6/1, 7-diyl-alt-2, 5-thiophene] (PDI-Th) exhibited the best power conversion efficiency (PCE) of 5.13%, with open-circuit voltage (V_oc)=0.79 V, short-circuit current density (J_sc)=12.35 mA·cm^-2 and fill-factor (FF)=0.52. The polymer of PDI-Th acceptor used here had a regio-irregular backbone, conveniently prepared from a mixture of 1, 6-and 1, 7-dibromo-PDI. It is also noteworthy that neither additive nor post-treatment is required for obtaining such a cell performance.

The efficiency of the poly (3-hexylthiophene) (P3HT) and[6, 6]-phenyl C₆₁-butyric acid methyl ester (PC₆₁BM) based organic solar cells was enhanced by using 1, 2, 4-trichlorobenzene (TCB) as a processing additive to control the blend morphology. The addition of TCB improved the arrangement of P3HT which resulted in good phase separated blend films. Correspondingly, the optimized solar cells showed a power conversion efficiency (PCE) of 4.17% with a fill factor (FF) of 0.69, which were higher than those of common thermal annealing devices (PCE 3.84%, FF 0.67). The efficiency was further improved to 4.74% by thermal annealing at 150¦ for 10 min with a higher FF of 0.74.

The strategy of sequentially spin-coating a perovskite film from the perovskite precursor and an electron transporting layer of[6, 6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) is developed to simplify the fabrication procedure of perovskite solar cells. X-ray diffraction and scanning electron microscopy indicate that PC₇₁BM film on perovskite layer can retard the evaporation of dimethyl sulfoxide (DMSO) efficiently, thus prolonging the transformation of intermediate phase to perovskite crystals, leading to a high quality perovskite thin film. The solar cells with the structure of indium tin oxides (ITO)/poly (3, 4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS)/CH₃NH₃PbI₃/PC₇₁BM/bathocuproine (BCP)/Ag made from this simplified method exhibit a higher efficiency (12.68%) than those from the conventional one-step method (9.49%).