Tuning the Molecular Weight of the Electron Accepting Polymer in All‐Polymer Solar Cells: Impact on Morphology and Charge Generation

Molecular weight is an important factor determining the morphology and performance of all‐polymer solar cells. Through the application of direct arylation polycondention, a series of batches of a fluorinated naphthalene diimide‐based acceptor polymer are prepared with molecular weight varying from M_n = 20 to 167 kDa. Used in conjunction with a common low bandgap donor polymer, the effect of acceptor molecular weight on solar cell performance, morphology, charge generation, and transport is explored. Increasing the molecular weight of the acceptor from M_n = 20 to 87 kDa is found to increase cell efficiency from 2.3% to 5.4% due to improved charge separation and transport. Further increasing the molecular weight to M_n = 167 kDa however is found to produce a drop in performance to 3% due to liquid–liquid phase separation which produces coarse domains, poor charge generation, and collection. In addition to device studies, a systematic investigation of the microstructure and photophysics of this system is presented using a combination of transmission electron microscopy, grazing‐incidence wide‐angle X‐ray scattering, near‐edge X‐ray absorption fine‐structure spectroscopy, photoluminescence quenching, and transient absorption spectroscopy to provide a comprehensive understanding of the interplay between morphology, photophysics, and photovoltaic performance.     

Acidochromicity of a low‐molecular‐weight pyrimidine‐based copolymer

A new type of low‐molecular‐weight polypyrimidine in a π‐conjugated main chain was prepared by a Grignard reaction between 2‐amino‐4,6‐dichloropyrimidine and 1,4‐dibromo‐2,5‐didodecyloxybenzene in the presence of [1,2‐Bis(diphenylphosphino) ethane]dichloronickel(II). The structure of the copolymer was fully elucidated by Fourier transform infrared spectroscopy, ¹H‐NMR, and elemental analysis. The copolymer had good solubility in common organic solvents. The copolymer displayed a bathochromic shift when protonated with an organic or inorganic acid in chloroform or tetrahydrofuran. The copolymer depicted facile p‐doping and good electron‐transporting electrochemical properties in a 1M H₂SO₄ aqueous solution. The copolymer showed a narrow polydispersity of 1.04. Thermogravimetric analysis showed that the copolymer had a certain thermal stability with no decomposition at a temperature of 250°C under N₂. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41174.     

Synthesis and properties of polymer from bis‐3,4‐ethylenedioxythiophene substituted acenaphthenequinoxaline

A new electrochoromic polymer poly(8,11‐bis(3,4‐ethylenedioxy thiophen‐2‐yl)acenaphtho[1,2‐b]‐quinoxaline) (PBEAQ) was synthesized by electrochemical polymerization of the corresponding monomer (BEAQ) in a 0.1 M tetraethylammonium tetrafluoroborate (TEABF₄) dichloromethane–acetonitrile (2 : 1, v : v) solution. The monomer and polymer were characterized by elemental analysis, ¹H‐NMR, IR, and UV‐vis spectroscopy. The electrochemical and optical properties of polymer were investigated by cyclic voltammetry and UV‐vis spectroscopy. Cyclic voltammetry and spectroelectrochemistry studies demonstrated that the polymer can be reversibly reduced and oxidized (both n‐ and p‐doped) between ?2 V and +1.5 V vs. Ag/Ag⁺. The polymer had a transmissive light blue color in the oxidized state and reddish color in the reduced state. Undoped polymer shows UV‐vis absorption peaks at 615 nm in solution, 650 nm in solid state, and has an optical band gap of 1.5 eV. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

聚丙烯粉料固相光接枝丙烯酸的研究

为了提高聚丙烯(PP)的亲水性和染色性,以二苯甲酮(BP)为光引发剂、使用固相光接枝反应装置,采用固相紫外光接枝法在PP粒料表面接枝丙烯酸(AA)单体,并研究了单体含量、引发剂用量、辐照时间和溶胀时间对接枝率的影响规律,以及PP接枝前后力学性能的变化。结果表明,AA用量为1mL、引发剂用量为0.15g、辐照时间为30min、溶胀时间为12h时的接枝率最高。接枝率为5.2%左右,上染率为43.4%时,接枝PP的拉伸强度降了1.37MPa,但断裂伸长率从358.3%增加到396.3%,说明丙烯酸适度接枝对力学性能影响不大。     

Unconventional Molecular Weight Dependence of Charge Transport in the High Mobility n‐type Semiconducting Polymer P(NDI2OD‐T2)

The charge transport and microstructural properties of five different molecular weight (MW) batches of the naphthalenediimide‐thiophene copolymer P(NDI2OD‐T2) are investigated. In particular, the field‐effect transistor (FET) performance and thin‐film microstructure of samples with MW varying from M_n = 10 to 41 kDa are studied. Unlike conventional semiconducting polymers such as poly(3‐hexylthiophene) where FET mobility dramatically drops with decreasing molecular weight, the FET mobility of P(NDI2OD‐T2)‐based transistors processed from 1,2‐dichlorobenzene is found to increase with decreasing MW. Using a combination of grazing‐incidence wide‐angle X‐ray scattering, near‐edge X‐ray absorption fine‐structure spectroscopy, atomic force microscopy, and resonant soft X‐ray scattering, the increase in FET mobility with decreasing MW is attributed to the pronounced increase in the orientational correlation length (OCL) with decreasing MW. In particular, the OCL is observed to systematically increase from <100 nm for the highest MW samples to ≈1 µm for the lowest MW samples. The improvement in OCL and hence mobility for low MW samples is attributed to the lack of aggregation of low MW chains in solution promoting backbone ordering, with the pre‐aggregation of chains in 1,2‐dichlorobenzene found to suppress longer‐range liquid crystalline order.     

含二噻基哒嗪的聚芳炔类衍生物的合成与性能研究

以四(三苯基磷)钯(Pd(PPh3)4)和CuI作为催化剂,在二异丙胺和四氢呋喃溶液中,采用宽能带的1,4-二乙炔基-2,5-二(十二烷氧基)苯(PE)和窄能带的3,6-双(5′-溴-2′-噻吩)-哒嗪(TPD)以不同配料比合成了一系列新型聚芳炔。长链烷氧基的存在使得此类聚合物在常用的有机溶剂中具有较好的溶解性和成膜性。通过对上述聚合物的紫外-可见吸收、荧光发射及循环伏安等基本性能进行探讨可知,共聚物在THF溶液中的荧光量子效率为51%～61%;随着共聚物中TPD含量的增加,共聚物薄膜的吸收起始波长及荧光发射波长均有红移。聚合物薄膜的最大发射峰位于540～551nm。