Contact Electrification Spectrum for Performance Enhancement Mechanism Investigation of Triboelectric Nanogenerators based on Silicone Elastomers with Different Surface Microstructures

Triboelectric nanogenerators(TENGs)based on conjunctive effects of contact electrification(CE)and electrostatic induction are emerging as a new mechanical energy harvesting and sensing technique for promising applications in smart wearables,Internet of Things(IoTs),etc.The surface microstructure of a flexible triboelectric material for the increase of surface area is a common strategy for performance enhancement of TENGs,but the real roles of surface microstructures on their output performance are still not explicit due to the lack of suitable analysis tool and rational experimental design.Taking advantages of the surface-sensitive characteristic of CE effect,this work exploited and developed the electric signal patterns generated by single impact of TENGs as a kind of CE spectrum to analyze and speculate the real roles of surface microstructures of flexible triboelectric materials on the output performance of TENGs.Firstly,four different kinds of surface microstructures,namely planar surface(PS)and three combinations of two basic surface microstructures,i.e.,micro lens arrays(MLAs),fabric textures(FTs),and hierarchical structures of MLAs on FTs(MLA/FTs),were elaborately designed and introduced for an identical triboelectric material(i.e.,silicone elastomer)by a(micro)molding synthesis route.Then they were used for assembly of TENGs based on vertical contact mode to conduct performance evaluation under the same triggering conditions.Through systematic analysis and comparison of their highly repeatable CE spectra by programmed machine,it was found that the surface microstructure for a flexible triboelectric material to maximally enhance the output performance of a TENG shall achieve a positive synergistic effect of increasing triboelectric charge density,effective contact area and contacting/separating velocity,rather than simple increase of its surface area.

Random Terpolymer Based on Simple Siloxane-functionalized Thiophene Unit Enabling High-performance Non-fullerene Organic Solar Cells

Incorporation of siloxane-functionalized units into polymers backbone has proven to be an efficient strategy to improve photovoltaic performance. In this work, a low-cost siloxane-containing unit was developed to construct a series of terpolymers, and the effects of siloxane on the polymer performance were systematically studied. Different contents of thiophene containing siloxane-functionalized side chain were introduced into PM6 to obtain a series of polymers(PM6, PM6-SiO-10, PM6-SiO-20 and PM6-SiO-30). The siloxane-functionalized side chains in polymers have only a slight effect on the absorption behavior and frontier molecular orbitals. However, when the siloxane content increased, the terpolymers' aggregation property decreased and the temperature-dependency increased, leading to improved donor-acceptor compatibility. The power conversion efficiency(PCE) based on PM6:Y6, PM6-SiO-20:Y6 and PM6-SiO-30:Y6 devices was 15.64%, 16.03% and 15.82%, respectively. In comparison, the active layer based on PM6-SiO-10:Y6 exhibits the most appropriate phase separation morphology, resulting in effective exciton dissociation, more balanced hole-electron transport and less recombination. Consequently, the highest PCE of 16.69% with an outstanding shortcircuit current density of 26.96 mA·cm^(-2) was obtained, which are one of the highest values for siloxane-functionalized polymer-based devices.This work demonstrates that finely controlling the content of siloxane-functionalized thiophene is beneficial for obtaining high-performance terpolymer donors and provides a novel and low-cost method to improve photovoltaic performance.

One-step preparation of branched PEG functionalized AIE-active luminescent polymeric nanoprobes

The synthesis of amphiphilic aggregation-induced emission （ALE） dyes based organic nanoparticles has recently attracted in- creasing attention in the biomedical fields. These AlE dyes based nanoparticles could effectively overcome the aggregation caused quenching effect of conventional organic dyes, making them promising candidates for fabrication of ultrabright organic luminescent nanomaterials. In this work, AIE-active luminescent polymeric nanoparticles （4-NH2-PEG-TPE-E LPNs） were facilely fabricated through Michael addition reaction between tetraphenylethene acrylate （TPE-E） and 4-arm-poly（ethylene glycol）-amine （4-NH2-PEG） in rather mild ambient. The 4-NH2-PEG can not only endow these AlE-active LPNs good water dispersibility, but also provide functional groups for further conjugation reaction. The size, morphology and luminescent prop- erties of 4-NH2-PEG-TPE-E LPNs were characterized by a series of techniques in detail. Results suggested that these AlE-active LPNs showed spherical morphology with diameter about 100-200 nm. The obtained 4-NH2-PEG-TPE-E LPNs display high water dispersibility and strong fluorescence intensity because of their self assembly and AlE properties of TPE-E. Biological evaluation results demonstrated that 4-NH2-PEG-TPE-E LPNs showed negative toxicity toward cancer cells and good fluorescent imaging performance. All of these features make 4-NHz-PEG-TPE-E LPNs promising candidates for biolog- ical imaging and therapeutic applications.

Alternating Terpolymers Based on Tunable Bi-donors with Manipulating Energy Levels and Molecular Geometry

Three novel regular acceptor-donorl-acceptor-donor2（A-D1-A-D2） terpolymers were prepared via em-bedding a second donor（D2） unit into the traditional D-A backbone to manipulate the energy levels and moleculargeometry with no complex synthesis or solubility loss. In these A-D1-A-D2 terpolymers, benzodithiophene（BDT, D1）and diketopyrrolopyrrole（DPP, A） were selected as the basic skeleton, and the dithienopyrrole（DTPy）, carbazole（CZ）and fluorine（FL） units with different electron donating ability were chosen as the second donor trait（D2）. The HOMOenergy levels can be effectively modulated by only varying D2 unit because of the push-pull interaction between do-nor and acceptor units. Versus the D-A bipolymer PDPP-BDT, incorporation of the D2 unit into the copolymers candistinctly lower the highest occupied molecular orbital（HOMO） levels to -5.47 eV for PDDPP-BDT-DTPy, -5.38 eVfor PDDPP-BDT-CZ and -5.23 eV for PDDPP-BDT-FL, which shows the strong dependence on electron-donatingability. Density functional theory（DFT） simulation and X-ray diffraction（XRD） measurements also reveal the effectof the D2 units on the molecular geometry of the terpolymers and their molecular packing. Notably, aPDDPP-BDT-DTPy combined with a thiophene ring and forked tail pendant away from the backbone had less back-bone torsion and more compact packing than the other two counterparts. These results demonstrate that embedding asecond donor（D2） unit into the backbone to construct an A-D1-A-D2 structure can be an effective and direct strategyto manipulate the energy levels and molecular geometry and develop organic semiconducting materials.

Highly stable Al-doped ZnO by ligand-free synthesis as general thickness-insensitive interlayers for organic solar cells

Highly conductive and dispersible Al-doped ZnO(AZO) nanoparticles(NPs) have been successfully prepared by ligand-free colloidal synthesis at low temperature and stabilization by surfactant-aid including ethanolamine(EA), ethylenediamine(EDA),diethylenetriamine(DETA) and triethylenetetramine(TETA). Due to the strong intermolecular hydrogen-bonding interactions between AZO NPs and the amino groups from surfactants, the inevitable aggregation was suppressed and the surface defect sites were passivated obviously. The existence of electron transfer from the nitrogen of the amino groups to the zinc of AZO,led to a dramatic increase in electrical conductivity. A homogeneous current intensity value up to ~2200 pA for AZO tread by DETA was characterized by conductive atomic force microscopy(C-AFM), which was more superior than that of the reported sol-gel synthesized AZO with the assistance of EA surfactant(refer to 170.7 pA). Furthermore, non-fullerenes solar cells based on PBDB-T:ITIC with AZO-DETA(80 nm) yielded a best device efficiency of 10.7% and kept up prominent PCE exceeding 10%even with more thicker interlayer(95 nm).

Diketopyrrolopyrrole-based Conjugated Polymers as Additives to Optimize Morphology for Polymer Solar Cells

Novel random copolymers for optimizing the morphology of the active layer for high performance organic photovoltaic devices have been demonstrated. Three ternary random copolymers PTBDTDPPSiCN（3/7）, PTBDTDPPSiCN（5/5）, PTBDTDPPSiCN（7/3） were prepared by polymerization of electron-donating thienyl-substituted benzodithiophene （TBDT） with 2,5-bis[8-（1,1,3,3,5,5,5-heptamethyltrisiloxane-3-yl）octly]-pyrrolo[3,4-c]pyrrole-1,4-dione （DPPSi） and 2,5-dio[5-（5-cyano-5,5-dimethyl-pentyl）]-3,6-dithiophen-2-yl-pyrrolo[3,4-c]pyrrole-1,4-dione （DPPCN） of different ratios. The DPPCN block can well-tune the light absorption and molecular packing, while the DPPSi block is in favor of enhancing the charge mobility. And the formation of organic Si--O--Si networks is beneficial to stabilize the morphology of the active layer. These new copolymers have narrow bandgaps and broaden visible light absorption from 500 nm to 1000 nm. Careful balance of the contents of the trimethoxysilyl group and the cyano group can well-tune the surface energy and morphology of the copolymers. Incorporation of these novel copolymers as additives into the blend of poly（3-hexylthiophene） （P3HT） and [6,6]-phenyl-C60-butyric acid methyl ester （PC61BM） is found to effectively broaden the light absorption, improve the compatibility and morphology of the active layer. As a result, some devices with certain ratios of these copolymers as additives achieve the enhanced efficiency compared with the device based on pristine P3HT：PC61BM.

Novel Donor-Acceptor Copolymers Based on Dithienosilole and Ketone Modified Thieno[3,4-b]thiophene for Photovoltaic Application

Two novel donor-acceptor （D-A） copolymers containing dithienosilole （DTS） donor unit and ketone modified thieno[3,4-b]thiophene （TT） acceptor unit, namely, poly{4,4＇-bis（2-ethylhexyl）dithieno[3,2-b：2＇,Y-d]silole-5,5＇-diyl- alt-l-（thieno[3,4-b]thiophen-2-yl）-2-ethylhexan-l-one} （PDTSTT） and poly{4,4＇-bis（2-ethylhexyl）dithieno[3,2- b：2＇,3＇-d]silole-5,5＇-diyl-alt- 1-（4,6-bis（4-ethylhexylthien-2-yl）thieno[3,4-b]thiophen-2-yl）-2-ethylhexan- 1-one} （PD- TSDTTT）, were synthesized for the application in polymer solar cells （PSCs）, and the effects of thiophene bridge on the structural geometry and photovoiltaie performance have been investigated. The polymer PDTSTT and PDTSDTTT have the electrochemical bandgaps of 1.54 and 2.02 eV, together with low-lying HOMO energy levels of-5.47 and -5.37 eV, respectively. Molecular geometry simulation result shows that compared with PDTSTT, the insertion of thiophene bridge in PDTSDTTT can well relieve the steric hindrance between the TT and DTS unit, as confirmed by the reduced dihedral angle between DTS and DTTT unit. Under the illumination of AM 1.5G, 100 mW/cm2, the PSC based on PDTSDTTT/PC61BM （1 ： 1, w ： w） demonstrates a power conversion efficiency of 1.0%, which is significantly improved in comparison with the device based on PDTSTT/PC61BM （1 ： 2, w ： w） under the same experimental condition. This is because the enhanced planarity and increased effective conjugation of the main chain in PDTSDTTT promote the more favorable morphology for charge transportation, although PDTSTT possesses the broader absorption band than PDTSDTTT.