烷基链支化位点对全稠环小分子受体聚集的影响（英文）_张永倩.pdf

Chem.J.Chinese Universities,2023,44(7),2023006820230068(1/11)CHEMICAL JOURNAL OF CHINESE UNIVERSITIES高 等 学 校 化 学 学 报研究论文烷基链支化位点对全稠环小分子受体聚集的影响张永倩1，2，朱小玉1，2，苗俊辉1，刘俊1，2，王利祥1，2（1.中国科学院长春应用化学研究所,高分子物理与化学国家重点实验室,长春130022；2.中国科学技术大学,合肥 230026）摘要 全稠环分子是一种具有优异稳定性的新型电子受体材料,可应用于有机太阳能电池.本文设计了2个具有不同吡咯单元上烷基链支化位点的全稠环小分子受体FM5与FM6,并研究了烷基链的支化位点对全稠环分子的光电性质和分子堆积性质的影响.与具有2号支化位点烷基链的FM5相比,具有3号支化位点烷基链的FM6展示出蓝移的吸收光谱和更高的结晶性.由于2号支化位点的烷基链具有更大的空间位阻,FM5在共混膜中表现出适宜的分子聚集行为,进而形成良好的共混膜形貌.将FM5作为受体制备有机太阳能电池器件,可以实现9.03%的能量转换效率,高于FM6(6.67%),这归因于合适的共混膜形貌.研究结果表明,侧链工程是调控全稠环分子聚集、结晶以及共混膜形貌的有效策略.关键词 全稠环分子；有机太阳能电池；电子受体；薄膜形貌；烷基链支化位点中图分类号 O626；TM914.4 文献标志码 A doi：10.7503/cjcu20230068Effect of Alkyl-chain Branching Position on Molecular Aggregation of All-fused-ring MoleculesZHANG Yongqian1，2，ZHU Xiaoyu1，2，MIAO Junhui1，LIU Jun1，2*，WANG Lixiang1，2（1.State Key Laboratory of Polymer Physics and Chemistry，Changchun Institute of，Applied Chemistry，Chinese Academy of Sciences，Changchun 130022，China；2.University of Science and Technology of China，Hefei 230026，China）Abstract All-fused-ring molecules are a novel type of electron acceptor materials with excellent intrinsic stability for organic solar cell（OSC）applications.In this work，we developed two all-fused-ring small molecular acceptors，FM5 and FM6，with different branching positions of alkyl chains on the pyrrole motif.The effects of branching points of the alkyl chains on optical and electronic properties，molecular stacking of the molecules were investigated.Compared with FM5 with 2nd-position branched alkyl chains，FM6 with 3rd-position branched alkyl chains exhibits the blue-shifted absorption and higher crystallinity.Due to the large steric hindrance caused by alkyl chains at 2nd branching sites，FM5 exhibits appropriate molecular aggregation and thus favorable film morphology in the blend film.Due to the suitable blend film morphology，the OSC device using FM5 as electron acceptor exhibits a power conversion efficiency（PCE）of 9.03%，which is higher than that of FM6（6.67%）.These results demonstrate that the side chain engineering is an effective strategy for tuning the molecular aggregation，crystalline and blend film morphology for all-fused-ring molecules.收稿日期：2023-02-15.网络首发日期：2023-03-24.联系人简介：刘 俊,男,博士,研究员,主要从事有机/高分子光电功能材料方面的研究.E-mail:基金项目：吉林省自然科学基金(批准号:20230101122JC)、国家自然科学基金(批准号:22135007,52073281),国家重点研发计划项目(批准号:2019YFA0705900)资助.Supported by the Natural Science Foundation of Jilin Province,China(No.20230101122JC),the National Natural Science Foundation of China(Nos.22135007,52073281)and the National Key Research and Development Program of China(No.2019YFA0705900).CHEMICAL JOURNAL OF CHINESE UNIVERSITIES高 等 学 校 化 学 学 报研究论文Chem.J.Chinese Universities,2023,44(7),2023006820230068(2/11)Keywords All-fused-ring molecule；Organic solar cell；Electron acceptor；Film morphology；Branching positions of alkyl chain1 IntroductionOrganic solar cells（OSCs）are recognized as one of the most potential technologies to replace conventional fuel energy with solar energy，due to their outstanding properties of light weight，low cost，mechanical flexibility and the possibility of semi-transparent/indoor photovoltaic application16.In recent years，OSCs have made impressive progress with power conversion efficiency（PCE）of over 19%in single-junction device，which mainly benefitted from the brilliant design strategy of active layer materials and ingenious device technologies710.Non-fullerene electron acceptors（NFAs）with A-D-A and A-DAD-A structures play an important role in the performance breakthrough of OSCs1114.However，for these highly efficient D-A-type acceptor molecules，the junction between the central core and the terminal units via the external vinyl double bonds is the most vulnerable position in the conjugated backbone，which significantly reduces the stability of these molecules and hinders their practical application1520.To solve this issue，the all-fused-ring strategy was proposed to improve the stability of the electron acceptors2126.For example，Duan et al.22 introduced amino groups and triggered the intramolecular cyclization to replace external vinyl units and design all-fused-ring molecule（DFA4）.Zhu et al.23，26 extended the indaceno 1，2-b：5，6-b dithiophene（IDT）core and benzo2，1，3-thiadiazole（BT）fused-ring core（BTP）to develop all-fused-ring molecules（ITYM and F13）.Recently，based on all-fused-ring strategy，our group developed a series of all-fused-ring molecules，which were A-DAD-A molecular backbones.These all-fused-ring molecules exhibited excellent intrinsic stability and can be used as electron acceptors for high-stability OSC devices.In chemical structure，small molecule acceptors are generally composed of a photosensitive-conjugated skeleton attached to several inert alkyl side chains.The basic function of alkyl side chains is to increase the solubility of molecules and ensure the solution processability of materials2729.On the other hand，side chains affect the molecular stacking in solid films and regulate the phase separation morphology of the blend films3033.Side chain modulation，including the type，length and branching point of alkyl chains，is an important tool to develop high-performance acceptor materials3440.For instance，Huang et al.35 synthesized an acceptor DTY6 by introducing more long-branching alkyl chain 2-decyltetradecyl to replace 2-ethylhexyl on the pyrrole of Y6.Due to the steric hindrance effect of the long-branching alkyl chains，DTY6 showed better aggregation domain size in the blend film，thus achieving higher efficiency.He et al.37 developed A-DAD-A type NFAs by introducing different alkyl chains（1-dodecyl，2-ethylhexyl，2-butyloctyl，and 2-hexyldecyl）into core units.BTIC-BO-4Cl with 2-butyloctyl side chains exhibits the best performance due to its short stacking distance，good film morphology and charge transport property.Li et al.36 designed and synthesized two isomeric A-DAD-A type NFAs with thienyl outer side chains attaching a 2-ethylhexyl substituent at the-or-position.Compared to-substituted o-THE，-substituted m-TEH shows closer-stacking，stronger intermolecular interaction and higher electron mobility，resulting in higher efficiency in OSC device.Compared with skeleton modification，side chain modulation to regulate molecular properties and device performance is less costly in synthesis exploration4144.The subtle changes in the structure of the side chains may have an unexpected effect on the photoelectronic properties.The all-fused-ring molecules，which have no rotatable single bond on the skeleton，are structurally different from the classical non-fullerene acceptor systems.In order to develop high-performance all-fused-ring acceptor materials，it is necessary to understand the relationship of the molecular structure，film stacking and blend morphology.In this manuscript，we developed two new all-fused-ring small molecule acceptors，FM5 and FM6，with CHEMICAL JOURNAL OF CHINESE UNIVERSITIES高 等 学 校 化 学 学 报研究论文Chem.J.Chinese Universities,2023,44(7),2023006820230068(3/11)different branching points of the alkyl chains on the nitrogen atoms（Fig.1）.The effects of branching points of the alkyl chains on optical and electronic properties，molecular stacking of the molecules and morphology of blend films were studied.Compared with FM5 with 2nd-position branched alkyl chains，FM6 with 3rd-position branched alkyl chains exhibits a blue-shifted absorption and stronger molecular aggregation.FM5 with the shorter distance of the branching position shows appropriate molecular packing and thus favorable nanoscale morphology of the blend films.Because of the appropriate blend film morphology，the OSC device based on FM5 exhibits a power conversion efficiency of 9.03%，which is higher than that of FM6.These results indicate that fine-tuning the branching positions of alkyl chains is an effective strategy to regulate molecular stacking and blend film morphology for OSCs.2 Experimental2.1Materials and InstrumentsAnhydrous sodium sulfate（Na2SO4），chloroform（CF），N，N-dimethylformamide，methanol，ethanol，isopropyl alcohol and acetone，A.R.，Beijing Chemical Industry Group Co.，Ltd.；anhydrous potassium carbonate（K2CO3，99%），anhydrous sodium chloride（NaCl，99.9%），potassium iodide（KI，99%），triethyl phosphite（98%），malononitrile（98%），titanium tetrachloride（TiCl4，99%），pivalic acid（99%），trans-bis（acetato）bis o-（di-o-tolylphosphino）benzyl dipalladium（II）（Herrmann s catalyst，98%），tris（2-methoxyphenyl）phosphineP（o-MeOPh）3，97%，cesium carbonate（Cs2CO3，99.9%），tetrabutylammonium hexafluorophosphate（98%），Energy Chemical（Shanghai）Pharmaceutical Chemistry Co.，Ltd.；chlorobenzene（CB），A.R.，Sinopharm Chemical Reagent Co.，Ltd.；1，2-dichlorobenzene（98%），2-bromo-4，5-difluorobenzoyl chloride（96%），Shanghai Aladdin Biochemical Technology Co.，Ltd.；petroleum ether，A.R.，dichloromethane（CH2Cl2），A.R.，Tianjin Fuyu Fine Chemical Co.，Ltd.；aluminum chloride（AlCl3），99%，Shanghai Macklin Biochemical Co.，Ltd.；1，8-diiodooctane（DIO，99.9%），zinc acetate dehydrate（99.9%），ethanolamine（99.9%）and 2-methoxyethanol（99.8%），Sigma-Aldrich（Shanghai）Trading Co.，Ltd.AV-500 MHz nuclear magnetic resonance（NMR）spectrometer，Switzerland Bruker Corporation；Daltonics Flex matrix-assisted laser desorption ionization time of flight mass spectrometer（MALDI-TOF-MS），Switzerland Bruker Corporation；Perkin Elmer TGA 7 Thermogravimetric Analyzer，America Perkin Elmer Inc.；Q2000 differential scanning calorimeter(DSC)instrument,America TA instruments；SPI3800NSPA300HVVEatomic force microscopy(AFM),Japan Seiko Instruments Inc.；Two-dimensional grazing incidence wide-angle X-ray scatterer，Australian Synchrotron ANSTO；UV-3600 spectrometer，Japan Shimadzu Corporation.2.2OSC Devices Fabrication and MeasurementThe OSC devices were fabricated with the inverted structure of ITO/ZnO/active layer/MoO3/Al.The prepatterned ITO-coated glass substrates were cleaned in an ultrasonic bath with deionized water for 10 min，isopropyl alcohol for 30 min，deionized water for 10 min，acetone for 10 min and isopropyl alcohol for 10 min Fig.1Chemical structures of FM5 and FM6CHEMICAL JOURNAL OF CHINESE UNIVERSITIES高 等 学 校 化 学 学 报研究论文Chem.J.Chinese Universities,2023,44(7),2023006820230068(4/11)in sequence，and then dried at 120 for over 60 min.After treated with ultraviolet-ozone for 30 min，ZnO layers（ca.30 nm）were spin-coated at 5000 r/min for 40 s onto the cleaned ITO glasses from ZnO precursor solution，and then thermal annealed at 200 for 60 min in air.The ZnO precursor was synthesized by dissolving zinc acetate dehydrate（1 g）and ethanolamine（280 mg）in 10 mL of 2-methoxyethanol under vigorous stirring for 10 h in air.The mass ratio of donor to acceptor was kept at 1.0 1.4 and the mixture was dissolved in CF at a concentration of 10 mg/mL.After stirred at 55 for 2 h and 80 for 2 h，the solution was added with 0.5%（volume fraction）DIO and then stirred for 30 min.Subsequently，the active layers （ca.90 nm）with different acceptors were generated by spin-coating from the CF solutions in a nitrogen-filled glove box.After dried for 40 min，the active layers were thermal annealed at 110 for 10 min.Then，the device fabrication was completed by thermally evaporating MoO3（ca.15 nm）and aluminum（ca.100 nm）under vacuum at a pressure of 2104 Pa.The active area of the devices，defined by a shadow mask，was 2 mm2.The current density-voltage（JV）curves of the OSC devices were measured using a computer-controlled Keithley 2400 Source Measure Unit under 100 mW/cm2 AM 1.5G simulated solar light illumination.An XES-40S2-CE class solar simulator （Japan，SAN-EI Electric Co.，Ltd）was used to provide the AM 1.5G simulated solar light illumination.A solar cell spectral response measurement system QE-R3011（Enli Technology Co.，Ltd.）was used to characterize the EQE spectrum under the short-circuit condition.The chopping frequency was 165 Hz.3 Results and Discussion3.1Synthesis and Characterization of FM5 and FM6Fig.1 shows the chemical structures of FM5 and FM6.The two molecules possess the same all-fused-ring molecular skeleton but different branching position of the alkyl chains on the nitrogen atoms.Compared with that of FM5，the branching site of alkyl chains on FM6 is further away from the molecular skeleton.The synthesis routes of the two molecules are shown in Scheme 1.The chemical structures of FM5 and FM6 were fully characterized using 1H NMR，13C NMR，matrix-assisted laser desorption ionization time of flight（MALDI-TOF）mass spectroscopy（MS）and elemental analysis.Both FM5 and FM6 are soluble well in common organic solvents，especially in chloroform with a solubility of 30 mg/mL for FM5 and 25 mg/mL for FM6 at room temperature.According to thermogravimetric analysis（TGA）shown in Fig.S1（see the supporting Scheme 1Synthetic routes of FM5 and FM6CHEMICAL JOURNAL OF CHINESE UNIVERSITIES高 等 学 校 化 学 学 报研究论文Chem.J.Chinese Universities,2023,44(7),2023006820230068(5/11)information of this paper），the thermal decomposition temperatures at 5%mass loss of FM5 and FM6 are 355 and 345，respectively，indicating that they have good thermal stability.According to differential scanning calorimetry（DSC）measurement，the two molecules exhibited distinct melting/crystallization peaks with the enthalpy change of 6.95/6.14 J/g for FM5 and 32.65/24.08 J/g for FM6，indicating higher crystallinity of FM6，as exhibited in Fig.S2 and Table S1（see the supporting information of this paper）.3.2Photophysical and Electrochemical Properties of FM5 and FM6The UV-Vis absorption spectra of FM5 and FM6 were measured in solution and in films.The results are shown in Fig.2 and Table 1.In solution，the two molecules exhibit similar absorption spectra with the maximum absorption wavelength at 763 nm.The maximum extinction coefficients are 8.7104 Lmol1cm1 for FM5 and 8.0104 Lmol1cm1 for FM6.From in solution to in thin film，the absorptions of both molecules display red-shifts.Notably，FM5 with 2nd-position branched alkyl chains exhibits a red-shift by 81 nm while FM6 with 3rd-position branched alkyl chains shows a red-shift of only 46 nm.FM5 displays a greater red-shift than FM6 from the solution to the film.This may be due to the difference in molecular packing caused by the different branching sites of alkyl chains on the nitrogen atoms.For FM5，the branching point of alkyl chains is close to the core，which may inhibit core-to-core interaction and facilitate the formation of J-aggregates（end-to-end arrangement of molecules）.In contrast，the alkyl-chains branching point of FM6 is far from the core，which may increase the formation of H-aggregations4547（core-to-core arrangement of molecules）.According to the onset wavelength of the absorption spectrum in films，the optical bandgaps（Egopt）of FM5 and FM6 are estimated to be 1.35 eV and 1.40 eV，respectively.Cyclic voltammetry was employed to determine the highest occupied molecular orbital（HOMO）and lowest unoccupied molecular orbital（LUMO）energy levels of the two molecules.From the onset oxidation and reduction potentials，the LUMO/HOMO energy levels of FM5 and FM6 are estimated to be 3.96 eV/5.65 e