- Effects of including electron-withdrawing atoms on the physical and photovoltaic properties of indacenodithieno[3,2-b]thiophene-based donor-acceptor polymers: towards an acceptor design for efficient polymer solar cells
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Three new D-A polymers PIDTT-DTBO, PIDTT-DTBT and PIDTT-DTFBT, using indacenodithieno[3,2-b]thiophene (IDTT) as the electron-rich unit and benzoxadiazole (BO), benzodiathiazole (BT) or difluorobenzothiadiazole (FBT) as the electron-deficient unit, were synthesized via a Pd-catalyzed Stille polymerization. The included electron-withdrawing atoms of the acceptor portion were varied between O, S, and F for tailoring the optical and electrochemical properties and the geometry of structures. Their effects on the film topography, photovoltaic and hole-transporting properties of the polymers were thoroughly investigated via a range of techniques. As expected, the stronger electron-withdrawing BO unit affords red-shifted absorption, low-lying HOMO and LUMO levels for the polymer PIDTT-DTBO. However, it depicts lower hole mobility and a less efficient charge collection in the active layer compared to the polymer PIDTT-DTBT. In addition, degradation of the solubility is observed in the fluorinated polymer PIDTT-DTFBT. As a result, a BHJ PSC (ITO/PEDOT:PSS/polymer:PC71BM/interlayer/Al) fabricated with PIDTT-DTBT attains the best power conversion efficiency (PCE) of 4.91%. These results thus demonstrate the potential effects of electronegative atoms on IDTT-based polymers and the structure-function correlations of such electron-donor materials for efficient PSCs.
- Cai, Ping,Xu, Xiaofeng,Sun, Jiangman,Chen, Junwu,Cao, Yong
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- Synthesis, optical properties, and electronic structures of nucleobase-containing π-conjugated oligomers
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The molecular recognition properties of the nucleobases instruct the formation of complex three-dimensional architectures in natural and synthetic systems; relatively unexplored is their use as building blocks for π-conjugated materials where they might mutually tune electronic and supramolecular structures. Toward this goal, an introductory set (1a-d and 2a-d) of six purine-terminated and two pyrimidine-terminated π-conjugated oligomers has been synthesized and used to develop experimental electronic and photophysical structure-property trends. Unlike 2,2′:5′,2″-terthiophene (TTT) derivatives 2a-d, intramolecular charge transfer dominates oligomers 1a-d bearing a 4,7-bisthienylbenzothiadiazole (TBT) spacer due to the strong electron-accepting ability of its benzothiadiazole (BTD) ring. The resulting donor-acceptor-donor systems feature lower HOMO-LUMO gaps than the terthiophene-linked nucleobases (ΔEg ～ 1.8 eV vs 2.4 eV based on electrochemical measurements), and the lowest so far for π-conjugated molecules that include nucleobases within the π-framework. Experiments reveal a dependence of photophysical and electronic structure on the nature of the nucleobase and are in good agreement with theoretical calculations performed at the B3LYP/6-31+G?? level. Overall, the results show how nucleobase heterocycles can be installed within π-systems to tune optical and electronic properties. Future work will evaluate the consequences of these information-rich components on supramolecular π-conjugated structure.
- Bou Zerdan, Raghida,Cohn, Pamela,Puodziukynaite, Egle,Baker, Matthew B.,Voisin, Maud,Sarun, Céline,Castellano, Ronald K.
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- Effect of fluorination pattern and extent on the properties of PCDTBT derivatives
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Herein, we report the synthesis of a series of fluorinated dithienyl carbazole-alt-benzothiadiazoles (PCDTBT analogues) and the characterisation of their optical, electrochemical, thermal and molecular organisation in the solid state. The polymers were decorated with fluorine on either the benzothiadiazole unit, carbazole unit or both to yield PCDTffBT, PCffDTBT and PCffDTffBT, respectively. The copolymers displayed decomposition temperatures in excess of 350°C. PCDTffBT, PCffDTBT and PCffDTffBT displayed optical band gaps of 1.86, 1.82 and 1.88 eV, respectively. It was speculated this was a consequence of the higher molecular weight of PCffDTBT relative to the other polymers. PCffDTBT and PCffDTffBT displayed shallower HOMO levels relative to PCDTffBT; a consequence of fluorinating the carbazole-donor moiety. XRD studies confirmed that fluorinating the benzothiadiazole-acceptor moiety improves molecular ordering by promoting π-π stacking of polymer backbones in solid state. Interestingly, fluorinating the carbazole-donor unit does not improve π-π stacking of polymer backbones.
- Cartwright, Luke,Yi, Hunan,Iraqi, Ahmed
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- n-Type core effect on perylene diimide based acceptors for panchromatic fullerene-free organic solar cells
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Perylene diimide (PDI) based high bandgap acceptors, DTBTP, DTF2BTP, and DTF2TZP, are synthesized for use in fullerene-free organic solar cells. The two PDI rings are connected to the end of the n-type core, forming a PDI-n-type core-PDI structure. Several n-type core materials, 4,7-dithieno-2,1,3-benzothiadiazole (DTBT), 5,6-difluoro-4,7-dithieno-2,1,3-benzothiadiazole (DTF2BT), and 4,6-difluoro-2H-benzo[d][1,2,3]triazole (DTF2TZ), are incorporated in the PDI acceptors and the n-type core effect on photovoltaic properties is studies. The introduction of alkyl side chains onto the core structure weakened the intermolecular interaction, whereas fluorination of the core structure improved the backbone planarity and intermolecular ordering. DTF2BTP having a planar core structure without bulky alkyl chains yielded the best power conversion efficiency, 4.41%, when mixed with PTB7-Th donor. The n-type core structure was beneficial in terms of increasing the electron accepting properties and the absorption in the high bandgap region of non-fullerene acceptors.
- Eom, Seung Hun,Kim, Hee Su,Do, Hee Jin,Lee, Un-Hak,Wibowo, Febrian Tri Adhi,Hwang, Do-Hoon,Yoon, Sung Cheol,Jung, In Hwan
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- Modification of a donor-acceptor photovoltaic polymer by integration of optoelectronic moieties into its side chains
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In this study, a strategy to modify photovoltaic properties of a known material by integrating certain optoelectronic moieties in its side chains has been described. Thus, a plenty of single and dendritic carbazole units were introduced into the side chains of poly(2,7-(9,9-dialkyl-fluorene)-alt-5,5′-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)) (PFDTBT), a famous donor-acceptor alternative conjugated polymer, to see what and how they can change the latter optoelectronic properties. It was found that such modifications not only increase the polymer light-harvesting capabilities in the UV region, but also enhance hole mobility in the pure film state. Furthermore, complicated photophysical and photochemical processes, including energy transfer, electron transfer and site-isolation effect, were observed to take place between carbazole units and the PFDTBT conjugated backbone. These factors work comprehensively and finally improve the polymer photovoltaic properties when modified with single carbazole units, but deteriorate when modified with dendritic carbazole units.
- Yu, Lin-Feng,Ge, Cong-Wu,Wang, Jin-Tu,Xiang, Xuan,Li, Wei-Shi
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- Donor-acceptor-structured naphtodithiophene-based copolymers for organic thin-film transistors
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New donor-acceptor (D-A) polymers, poly(4,5-bis(2-octyldodecyloxy)naphto[2,1-b:3,4-b']dithiophenebenzo[c][1,2,5]thiadiazole) (PNDT-B) and poly(4,5-bis(2-octyldodecyloxy)naphto [2,1-b:3,4-b′]dithiophene-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole) (PNDT-TBT), with the extended π-electron delocalization of naphtho[2,1-b:3,4-b']dithiophene, were successfully synthesized by Suzuki and Stille coupling reactions. The structure and physical properties of polymers were characterized by DFT calculation, UV-vis absorption, cyclovoltammetry, TGA and DSC analyses. X-ray diffraction studies indicated a relatively highly ordered intermolecular structure in PNDT-TBT after annealing. This high degree of molecular order resulted from the crystallinity and increasing planarity, provided by the thiophene linker groups and the interdigitation of the long alkoxy side chains. The new D-A polymer, PNDT-TBT, exhibited a p-type carrier mobility of 0.028 cm2/Vs and an on/off ratio of 5.9 × 103.
- Kim, Myeong-Jong,Seul Lee, Ye,Chul Shin, Sung,Kim, Yun-Hi
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- Linking design and properties of purine-based donor-acceptor chromophores as optoelectronic materials
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Creating new building blocks for donor-acceptor conjugated systems is an important task for continued development of materials for organic electronics. Purines were introduced into small-molecule π-conjugated systems via Stille cross-coupling using stannylated derivatives of benzodithiophene, thiophene, or dithienylbenzothiadiazole to generate a series of "purine-π-purine" chromophores having high thermal stability, long excited-state lifetimes, and high quantum yields. Photophysical and electrochemical property characterization indicate that depending on the choice of a conjugated bridging unit, purines behave as either an electron-donating or an electron-accepting unit in these small-molecule donor-acceptor chromophores. Specifically, while purine chromophores do not exhibit charge transfer character when linked to a thiophene unit, purinyl units act as a weak acceptor when coupled with benzodithiophene and as a weak donor when coupled with dithienylbenzothiadiazole. In addition to fundamental insights into the molecular design of purine-based chromophores and their charge-transfer character, the results and synthetic tailorability of purines suggest that they may be compelling building blocks in conjugated materials for optical and electronic devices and sensors.
- Collier, Graham S.,Brown, Lauren A.,Boone, Evan S.,Kaushal, Meesha,Ericson, M. Nance,Walter, Michael G.,Long, Brian K.,Kilbey, S. Michael
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p. 6891 - 6898
(2017/07/22)
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- High charge carrier mobility, low band gap donor-acceptor benzothiadiazole-oligothiophene based polymeric semiconductors
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A series of benzothiadiazole oligothiophene and oligo(thienylene vinylene) donor-acceptor (D-A) copolymers were synthesized and characterized. These low optical band gap materials (～1.5 eV) are capable of absorbing photons in the range of 400-800 nm and exhibit good thermal stability. Their hole mobilities, determined using an organic field-effect transistor (OFET) architecture, vary over a range of 3 orders of magnitude and strongly correlate with the molecular ordering and morphology of the respective thin films. Spin-coated films of the poly(benzothiadiazole-sexithiophene) PBT6, which exhibits a highly crystalline lamellar π-π stacked edge-on orientation on the OFET substrate, possesses a hole mobility of ca. 0.2 cm2/V·s. Vinylene-containing analogs PBT6V2 and PBT6V2′ are amorphous and exhibit very low mobilities. The molecular weight of PBT6 has a strong influence on the electronic properties: a sample with a lower molecular weight exhibits a mobility approximately 1 order of magnitude lower than the high molecular weight homologue, and the absorption maximum is appreciably blue-shifted. The hole mobility of PBT6 is further enhanced by a factor of ca. 3 through fabrication of the OFET by drop casting. OFETs fabricated by this process exhibit mobilities of up to 0.75 cm2/V·s and ION/OFF ratios in the range of 106-107. These results demonstrate the potential of incorporating benzothiadiazole units into polythiophene derivatives to develop high-mobility semiconducting polymers.
- Fu, Boyi,Baltazar, Jose,Hu, Zhaokang,Chien, An-Ting,Kumar, Satish,Henderson, Clifford L.,Collard, David M.,Reichmanis, Elsa
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p. 4123 - 4133
(2013/01/15)
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