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Conjugated copolymers of triazoloquinoxaline-alt-fluorene with imine chain bridge for photovoltaic solar cells
Materials Letters 175 (2016) 223–226
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Conjugated copolymers of triazoloquinoxaline-alt-fluorene with imine chain bridge for photovoltaic solar cells Ling Li, Zhenhuan Lu, Jianwei Yang, Ming Li, Linzhi Zhang, Jiefeng Hai n, Yongping Liu n Guangxi Key Laboratory of Electrochemical and Magneto-chemical Functional Materials, College of Chemistry and Bioengineering, Guilin University of Technology, Guilin 541004, China
art ic l e i nf o
a b s t r a c t
Article history: Received 28 January 2016 Received in revised form 28 March 2016 Accepted 2 April 2016 Available online 4 April 2016
A series of copolymers based on triazoloquinoxaline and fluorene derivatives have been synthesized by Suzuki polycondensation, which have aryl imine chain bridge in fluorene unit. N-(aryl) 9H-fluoren-9imine was first synthesized and used to construct conjugated polymers, which were applied in organic photovoltaics. The thermal, electrochemical, and photovoltaic properties were characterized. These good solution-processable copolymers showed broad absorption from 350 nm to 800 nm region with the optical bandgap of 1.55 eV. Preliminary bulk heterojunction solar cells of P3:PC61BM (1:2 w/w) exhibited maximum power conversion efficiency of 1.56% with Jsc of 4.50 mA cm 2, Voc of 0.79 V, and FF of 0.44. & 2016 Elsevier B.V. All rights reserved.
Keywords: Solar energy materials Semiconductors organic polymer solar cells N-(aryl) 9H-fluoren-9-imine
1. Introduction Bulk heterojunction (BHJ) [1] polymer solar cells (PSCs) have drawn considerable interests in the field of renewable energy generation technologies, mainly due to their potential in massproduction of low cost, light-weight and large-scale flexible devices [2]. Significant progress has been achieved in pursuing highperformance BHJ devices, with a champion record of power conversion efficiency (PCE) over 11.8% [3]. Great efforts have been made in novel materials development (e.g. narrow bandgap polymers [4,5] and fullerene derivatives [6]), device engineering (e.g. tandem [7], inverted [8] and ternary [9] structure design, as well as annealing, solvent processing [10] and interfacial modifications [11]). However, the PCEs obtained from small-area devices are still far away from the commercialization. For the development of donor-acceptor (D-A) structural narrow bandgap polymer, the matching of D and A unit is a great concern in structure design. Previous we have synthesized series of conjugated polymers based on fluorene and triazoloquinoxaline [12] for PSCs [13,14]. To further fine-adjust donor unit electron affinity, two-dimensional (2D) fluorene called N-(aryl) 9H-fluoren-9imine was developed. By conjugated imine chain bridge on fluorene 9 position, an extended π-conjugation system was constructed to form a highly rigid coplanar backbone. The structures provided n
Corresponding authors: E-mail addresses: [email protected] (J. Hai), [email protected] (Y. Liu).
http://dx.doi.org/10.1016/j.matlet.2016.04.009 0167-577X/& 2016 Elsevier B.V. All rights reserved.
strong intermolecular π-overlapping and electron-donating/accepting properties to enhance charge separation, transport, and energy-level tunability. Polymer based on imine chain bridge donor unit showed unprecedented precision tuned HOMO/LUMO energy levels reported by other group [15]. However, copolymers based on different substituent aryl fluoren-9-imine have never been reported. Further correlation studies on the different structure of imine chain bridge alternating polymers with same acceptor unit and their physiochemical properties might offer some helpful insight in designing novel narrow bandgap polymers. In this work, novel electron donor units and narrow bandgap copolymers based on aryl fluoren-9-imine and triazoloquinoxaline unit were designed and prepared for the first time. The correlation studies of aryl fluoren-9-imine unit structure with the optical, electronic properties and photovoltaic performance of the resulted polymers (see Scheme 1) were presented. The best device delivered a maximum PCE of 1.56%, with an open circuit voltage (Voc) of 0.79 V, a short circuit current (Jsc) of 3.31 mA/cm2 and a fill factor (FF) of 44%.
2. Materials and methods All the starting materials were utilized by purchasing commercially without further purification. The synthetic route of monomers and copolymers were shown in Scheme 1, and the detailed synthetic procedures were presented in the Supporting
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L. Li et al. / Materials Letters 175 (2016) 223–226
Scheme 1. Synthetic route for monomers and copolymers.
Table 1 Molecular weights, thermal property, bandgap and energy levels of the polymers. polymers
Mwa
M na
PDIa
Tdb (°C)
λmax (nm)c
λmax (nm)d
λonset (nm)d
Egopt (eV)
HOMO (eV)
LUMO (eV)
P1 P2 P3
32,790 22,816 23,852
12,100 9200 8900
2.71 2.48 2.68
387 400 393
657 629 606
700 660 629
0.80 0.79 0.98
1.50 1.56 1.55
5.20 5.19 5.38
3.70 3.63 3.83
a b c
Mw, Mn, and PDI of the polymers were determined by GPC using polystyrene standards in THF. The 5% weight-loss temperatures under N2 and heat from 50 to 800 °C at a rate of 20 °C/min. Solution. d Film.
material. Suzuki cross-coupling reaction was employed for the synthesis of P1-P3. These copolymers showed excellent solubility in organic solvents, including THF, CHCl3 and o-dichlorobenzene. The gel permeation chromatography (GPC) results indicated that three copolymers have the number-average molecular weight (Mn) of 8–12 kDa with a PDI of 2.4 2.7 (Table 1). P2 and P3 showed a low Mn, probably due to the strong electron affinity substituent of benzene unit resulted to polymerize inefficiency [15].
3. Results and discussion 3.1. Thermal properties, absorption properties and electrochemical properties All copolymers exhibited good thermal stability with decomposition temperature (Td) (5% weight loss) at 387, 400 and 392 °C for P1, P2 and P3, respectively (Fig. 1a). Fig. 1(b and c) showed the UV–vis absorption spectra of monomers and polymers in CHCl3 solution or film. The monomers displayed an absorption band in the range of 300–500 nm. Monomer 3a displayed most broad absorption band, which had suspended naphthalene. There was a contradictory conclusion that electron accepting group (such as – OCF3 and –F) had absorption band blue-shifted than electron donating group (naphthalene and –CH3). The results illustrated that differ substituents could tune aryl fluoren-9-imine backbone absorption band where donating group's conjugated effect was stronger than accepting group's induced effect through C¼ N bonding. These polymers films exhibited a broad absorption band in the range of 300–800 nm, which was 20–40 nm red-shifted in compassion to their absorption spectra in solution. The red-shifted absorption of polymers film indicated that strong intermolecular interaction and aggregation exist in the solid-state of these polymers. They all exhibited two evident absorption bands, the shorter wavelength absorption band was attributed to the π-π* transition
of the conjugated main chain and the longer wavelength was owed to the internal charge transfer interaction between the aryl fluoren-9-imine donating unit and BTzQx accepting unit. It was revealed that substituted aryl fluoren-9-imine stronger broaden spectrum absorption than alkyl fluoren-9-ylidene [13,16]. The optical bandgaps (Egopt) of copolymers were determined from the UV–vis absorption onsets in the solid state according to the empirical equation: Egopt ¼1240/λonset eV. The Egopt of P1, P2 and P3 were determined to be 1.56, 1.50 and 1.55 eV, respectively. the Egopt data of polymers could conclude that Egopt of polymers was mainly dependent upon their electron-withdrawing ability of polymer backbone, but a little effect of substituted aryl fluoren-9imine. The results also indicated that the incorporating of the different electron affinity unit into the backbone of polymer should be an effective method to finely control the optical bandgap and absorption band. The highest occupied molecular orbital (HOMO) energy levels of the conjugated polymers were determined by electrochemical cyclic voltammetry (CV) (seen Fig. s34). The HOMO level of the polymers were calculated from the onset oxidation potentials (Eox), while the LUMO levels were calculated using HOMO and optical Egopt according to the following equations [17]: HOMO ¼ e(Eox þ 4.4) (eV); LUMO ¼ HOMOþ Egopt (eV). The onset potential for oxidation (Eox) were observed to be 0.79, 0.80, and 0.98 eV for P1, P2 and P3, respectively. Accordingly, the corresponding HOMO energy level of P1, P2 and P3 were calculated to be 5.19, 5.20 and 5.38 eV, respectively. The deep HOMO levels of these polymers should be beneficial to their chemical stability and be desirable for higher Voc of the PSCs [18]. The LUMO level of P1, P2 and P3 were thus calculated to be 3.70, 3.63, 3.83 eV, respectively. The HOMOLUMO energy diagrams of the polymers and PC61BM were shown in Fig. 2a.
L. Li et al. / Materials Letters 175 (2016) 223–226
225
Fig. 1. TGA curve of polymers (a), absorption spectra in dilute CHCl3 solution of monomers (b), absorption spectra in dilute CHCl3 solution (c) and solid film of polymers (d).
4. Photovoltaic properties The preliminary photovoltaic properties of polymers were evaluated in BHJ solar cells by using polymer as electron donor and PC61BM as electron acceptor. To balance the absorbance and the charge transporting network of the photoactive layer, the weight ratios of copolymer and PC61BM were varied from 1:0.8 to 1:2. The polymer/PC61BM weight ratio of 1:2 showed the best device performance. The current density-voltage (J-V) curve was
shown in Fig. 2b. At a 1:2 weight ratio of P3/PC61BM, the device with P3/PC61BM as the active layer gave an open-circuit voltage (Voc) of 0.79 V, a short circuit current (Jsc) of 4.50 mA cm 2, a fill factor (FF) of 44%, and resulted in a power conversion efficiency (PCE) of 1.56%. (Fig. 2b and Table 2). Additionally, no further improvement was observed when using 1,8-diiodooctane (DIO) as an additive. We are going to improve the performance of solar cells by the optimization of film morphology and device fabrication conditions [19], such as methanol treatment or solvent annealing.
Fig. 2. The energy levels of copolymers (a) and J-V curves of PSCs with the weight ratios of copolymer and PC61BM 1:2 (b).
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L. Li et al. / Materials Letters 175 (2016) 223–226
Table 2 Photovoltaic properties of polymer solar cells based polymer:PC61BM (1:2) blended. Polymer/ PC61BM
Cathode
Voc [V]
Jsc [mA/cm2]
FF [%]
PCE [%]
P1 P2 P3
PFN/Ca/Al PFN/Ca/Al PFN/Ca/Al
0.72 0.75 0.79
2.48 2.84 4.50
62 32 44
1.08 0.68 1.56
5. Conclusion A new electron-donating unit, N-(aryl) 9H-fluoren-9-imine with different substituents, were developed and used for the design of D-A polymer for PSCs application for the first time. By conjugated aromatic ring with flourene unit, N-(aryl) 9H-fluoren-9-imine showed more planar conformation and electron donating ability. Based on N-(aryl) 9H-fluoren-9-imine with different substituents and BTzQx the narrow bandgap copolymers, exhibited an ideal bandgap of 1.55 eV. Primary device tests delivered a best PCE of 1.56% without any processing additives. This work has suggested that N-(aryl) 9H-fluoren-9-imine with different substituents unit could be a good choice of donor to construct fine-tuning physicochemical and photovoltaic properties of D-A polymers for PSCs.
Acknowledgments This work was financially supported by the National Natural Science Foundation of China (51202040, 21363006, 21563007 and 21201047), the Guangxi Natural Science Foundation (2015GXNSFBA139228).
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2016.04.009.
References [1] G. Yu, J. Gao, J.C. Hummelen, F. Wudl, A.J. Heeger, Science 270 (1995) 1789–1791. [2] Q. Gan, F.J. Bartoli, Z.H. Kafafi, Adv. Mater. 25 (2013) 2385–2396. [3] A.R.b.M. Yusoff, D. Kim, H.P. Kim, F.K. Shneider, W.J. da Silva, J. Jang, Energy Environ. Sci. 8 (2015) 303–316. [4] L. Dou, Y. Liu, Z. Hong, G. Li, Y. Yang, Chem. Rev. 115 (2015) 12633–12665. [5] I. Etxebarria, J. Ajuria, R. Pacios, Org. Electron. 19 (2015) 34–60. [6] G. Sauvé, R. Fernando, J. Phys. Chem. Lett. 6 (2015) 3770–3780. [7] C.C. Chen, W.H. Chang, K. Yoshimura, K. Ohya, J. You, J. Gao, Z. Hong, Y. Yang, Adv. Mater. 26 (2014) 5670–5677. [8] W. Yue, T.T. Larsen-Olsen, X. Hu, M. Shi, H. Chen, M. Hinge, et al., J. Mater. Chem. A 1 (2013) 1785–1793. [9] Y. Zhang, D. Deng, K. Lu, J. Zhang, B. Xia, Y. Zhao, et al., Adv. Mater. 27 (2015) 1071–1076. [10] B. Fu, C.-Y. Wang, B.D. Rose, Y. Jiang, M. Chang, P.-H. Chu, et al., Chem. Mater. 27 (2015) 2928–2937. [11] J. Zou, C.-Z. Li, C.-Y. Chang, H.-L. Yip, A.K.Y. Jen, Adv. Mater. 26 (2014) 3618–3623. [12] J. Hai, Y. Li, L. Yin, E. Zhu, L. Bian, W. Yu, et al., Polym. Chem. 5 (2014) 1163–1172. [13] J. Hai, B. Zhao, F. Zhang, C.-X. Sheng, L. Yin, Y. Li, et al., Polymer 54 (2013) 4930–4939. [14] J. Hai, B. Zhao, E. Zhu, L. Bian, H. Wu, W. Tang, Macromol. Chem. Phys. 214 (2013) 2473–2479. [15] J.D. Azoulay, Z.A. Koretz, B.M. Wong, G.C. Bazan, Macromolecules 46 (2013) 1337–1342. [16] C. Du, C. Li, W. Li, X. Chen, Z. Bo, C. Veit, et al., Macromolecules 44 (2011) 7617–7624. [17] W. Tang, L. Ke, L. Tan, T. Lin, T. Kietzke, Z.-K. Chen, Macromolecules 40 (2007) 6164–6171. [18] L. Bian, E. Zhu, J. Tang, W. Tang, F. Zhang, Prog. Polym. Sci. 37 (2012) 1292–1331. [19] Y. Huang, E.J. Kramer, A.J. Heeger, G.C. Bazan, Chem. Rev. 114 (2014) 7006–7043.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Conjugated copolymers of triazoloquinoxaline-alt-fluorene with imine chain bridge for photovoltaic solar cells Ling Li, Zhenhuan Lu, Jianwei Yang, Ming Li, Linzhi Zhang, Jiefeng Hai n, Yongping Liu n Guangxi Key Laboratory of Electrochemical and Magneto-chemical Functional Materials, College of Chemistry and Bioengineering, Guilin University of Technology, Guilin 541004, China
art ic l e i nf o
a b s t r a c t
Article history: Received 28 January 2016 Received in revised form 28 March 2016 Accepted 2 April 2016 Available online 4 April 2016
A series of copolymers based on triazoloquinoxaline and fluorene derivatives have been synthesized by Suzuki polycondensation, which have aryl imine chain bridge in fluorene unit. N-(aryl) 9H-fluoren-9imine was first synthesized and used to construct conjugated polymers, which were applied in organic photovoltaics. The thermal, electrochemical, and photovoltaic properties were characterized. These good solution-processable copolymers showed broad absorption from 350 nm to 800 nm region with the optical bandgap of 1.55 eV. Preliminary bulk heterojunction solar cells of P3:PC61BM (1:2 w/w) exhibited maximum power conversion efficiency of 1.56% with Jsc of 4.50 mA cm 2, Voc of 0.79 V, and FF of 0.44. & 2016 Elsevier B.V. All rights reserved.
Keywords: Solar energy materials Semiconductors organic polymer solar cells N-(aryl) 9H-fluoren-9-imine
1. Introduction Bulk heterojunction (BHJ) [1] polymer solar cells (PSCs) have drawn considerable interests in the field of renewable energy generation technologies, mainly due to their potential in massproduction of low cost, light-weight and large-scale flexible devices [2]. Significant progress has been achieved in pursuing highperformance BHJ devices, with a champion record of power conversion efficiency (PCE) over 11.8% [3]. Great efforts have been made in novel materials development (e.g. narrow bandgap polymers [4,5] and fullerene derivatives [6]), device engineering (e.g. tandem [7], inverted [8] and ternary [9] structure design, as well as annealing, solvent processing [10] and interfacial modifications [11]). However, the PCEs obtained from small-area devices are still far away from the commercialization. For the development of donor-acceptor (D-A) structural narrow bandgap polymer, the matching of D and A unit is a great concern in structure design. Previous we have synthesized series of conjugated polymers based on fluorene and triazoloquinoxaline [12] for PSCs [13,14]. To further fine-adjust donor unit electron affinity, two-dimensional (2D) fluorene called N-(aryl) 9H-fluoren-9imine was developed. By conjugated imine chain bridge on fluorene 9 position, an extended π-conjugation system was constructed to form a highly rigid coplanar backbone. The structures provided n
Corresponding authors: E-mail addresses: [email protected] (J. Hai), [email protected] (Y. Liu).
http://dx.doi.org/10.1016/j.matlet.2016.04.009 0167-577X/& 2016 Elsevier B.V. All rights reserved.
strong intermolecular π-overlapping and electron-donating/accepting properties to enhance charge separation, transport, and energy-level tunability. Polymer based on imine chain bridge donor unit showed unprecedented precision tuned HOMO/LUMO energy levels reported by other group [15]. However, copolymers based on different substituent aryl fluoren-9-imine have never been reported. Further correlation studies on the different structure of imine chain bridge alternating polymers with same acceptor unit and their physiochemical properties might offer some helpful insight in designing novel narrow bandgap polymers. In this work, novel electron donor units and narrow bandgap copolymers based on aryl fluoren-9-imine and triazoloquinoxaline unit were designed and prepared for the first time. The correlation studies of aryl fluoren-9-imine unit structure with the optical, electronic properties and photovoltaic performance of the resulted polymers (see Scheme 1) were presented. The best device delivered a maximum PCE of 1.56%, with an open circuit voltage (Voc) of 0.79 V, a short circuit current (Jsc) of 3.31 mA/cm2 and a fill factor (FF) of 44%.
2. Materials and methods All the starting materials were utilized by purchasing commercially without further purification. The synthetic route of monomers and copolymers were shown in Scheme 1, and the detailed synthetic procedures were presented in the Supporting
224
L. Li et al. / Materials Letters 175 (2016) 223–226
Scheme 1. Synthetic route for monomers and copolymers.
Table 1 Molecular weights, thermal property, bandgap and energy levels of the polymers. polymers
Mwa
M na
PDIa
Tdb (°C)
λmax (nm)c
λmax (nm)d
λonset (nm)d
Egopt (eV)
HOMO (eV)
LUMO (eV)
P1 P2 P3
32,790 22,816 23,852
12,100 9200 8900
2.71 2.48 2.68
387 400 393
657 629 606
700 660 629
0.80 0.79 0.98
1.50 1.56 1.55
5.20 5.19 5.38
3.70 3.63 3.83
a b c
Mw, Mn, and PDI of the polymers were determined by GPC using polystyrene standards in THF. The 5% weight-loss temperatures under N2 and heat from 50 to 800 °C at a rate of 20 °C/min. Solution. d Film.
material. Suzuki cross-coupling reaction was employed for the synthesis of P1-P3. These copolymers showed excellent solubility in organic solvents, including THF, CHCl3 and o-dichlorobenzene. The gel permeation chromatography (GPC) results indicated that three copolymers have the number-average molecular weight (Mn) of 8–12 kDa with a PDI of 2.4 2.7 (Table 1). P2 and P3 showed a low Mn, probably due to the strong electron affinity substituent of benzene unit resulted to polymerize inefficiency [15].
3. Results and discussion 3.1. Thermal properties, absorption properties and electrochemical properties All copolymers exhibited good thermal stability with decomposition temperature (Td) (5% weight loss) at 387, 400 and 392 °C for P1, P2 and P3, respectively (Fig. 1a). Fig. 1(b and c) showed the UV–vis absorption spectra of monomers and polymers in CHCl3 solution or film. The monomers displayed an absorption band in the range of 300–500 nm. Monomer 3a displayed most broad absorption band, which had suspended naphthalene. There was a contradictory conclusion that electron accepting group (such as – OCF3 and –F) had absorption band blue-shifted than electron donating group (naphthalene and –CH3). The results illustrated that differ substituents could tune aryl fluoren-9-imine backbone absorption band where donating group's conjugated effect was stronger than accepting group's induced effect through C¼ N bonding. These polymers films exhibited a broad absorption band in the range of 300–800 nm, which was 20–40 nm red-shifted in compassion to their absorption spectra in solution. The red-shifted absorption of polymers film indicated that strong intermolecular interaction and aggregation exist in the solid-state of these polymers. They all exhibited two evident absorption bands, the shorter wavelength absorption band was attributed to the π-π* transition
of the conjugated main chain and the longer wavelength was owed to the internal charge transfer interaction between the aryl fluoren-9-imine donating unit and BTzQx accepting unit. It was revealed that substituted aryl fluoren-9-imine stronger broaden spectrum absorption than alkyl fluoren-9-ylidene [13,16]. The optical bandgaps (Egopt) of copolymers were determined from the UV–vis absorption onsets in the solid state according to the empirical equation: Egopt ¼1240/λonset eV. The Egopt of P1, P2 and P3 were determined to be 1.56, 1.50 and 1.55 eV, respectively. the Egopt data of polymers could conclude that Egopt of polymers was mainly dependent upon their electron-withdrawing ability of polymer backbone, but a little effect of substituted aryl fluoren-9imine. The results also indicated that the incorporating of the different electron affinity unit into the backbone of polymer should be an effective method to finely control the optical bandgap and absorption band. The highest occupied molecular orbital (HOMO) energy levels of the conjugated polymers were determined by electrochemical cyclic voltammetry (CV) (seen Fig. s34). The HOMO level of the polymers were calculated from the onset oxidation potentials (Eox), while the LUMO levels were calculated using HOMO and optical Egopt according to the following equations [17]: HOMO ¼ e(Eox þ 4.4) (eV); LUMO ¼ HOMOþ Egopt (eV). The onset potential for oxidation (Eox) were observed to be 0.79, 0.80, and 0.98 eV for P1, P2 and P3, respectively. Accordingly, the corresponding HOMO energy level of P1, P2 and P3 were calculated to be 5.19, 5.20 and 5.38 eV, respectively. The deep HOMO levels of these polymers should be beneficial to their chemical stability and be desirable for higher Voc of the PSCs [18]. The LUMO level of P1, P2 and P3 were thus calculated to be 3.70, 3.63, 3.83 eV, respectively. The HOMOLUMO energy diagrams of the polymers and PC61BM were shown in Fig. 2a.
L. Li et al. / Materials Letters 175 (2016) 223–226
225
Fig. 1. TGA curve of polymers (a), absorption spectra in dilute CHCl3 solution of monomers (b), absorption spectra in dilute CHCl3 solution (c) and solid film of polymers (d).
4. Photovoltaic properties The preliminary photovoltaic properties of polymers were evaluated in BHJ solar cells by using polymer as electron donor and PC61BM as electron acceptor. To balance the absorbance and the charge transporting network of the photoactive layer, the weight ratios of copolymer and PC61BM were varied from 1:0.8 to 1:2. The polymer/PC61BM weight ratio of 1:2 showed the best device performance. The current density-voltage (J-V) curve was
shown in Fig. 2b. At a 1:2 weight ratio of P3/PC61BM, the device with P3/PC61BM as the active layer gave an open-circuit voltage (Voc) of 0.79 V, a short circuit current (Jsc) of 4.50 mA cm 2, a fill factor (FF) of 44%, and resulted in a power conversion efficiency (PCE) of 1.56%. (Fig. 2b and Table 2). Additionally, no further improvement was observed when using 1,8-diiodooctane (DIO) as an additive. We are going to improve the performance of solar cells by the optimization of film morphology and device fabrication conditions [19], such as methanol treatment or solvent annealing.
Fig. 2. The energy levels of copolymers (a) and J-V curves of PSCs with the weight ratios of copolymer and PC61BM 1:2 (b).
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L. Li et al. / Materials Letters 175 (2016) 223–226
Table 2 Photovoltaic properties of polymer solar cells based polymer:PC61BM (1:2) blended. Polymer/ PC61BM
Cathode
Voc [V]
Jsc [mA/cm2]
FF [%]
PCE [%]
P1 P2 P3
PFN/Ca/Al PFN/Ca/Al PFN/Ca/Al
0.72 0.75 0.79
2.48 2.84 4.50
62 32 44
1.08 0.68 1.56
5. Conclusion A new electron-donating unit, N-(aryl) 9H-fluoren-9-imine with different substituents, were developed and used for the design of D-A polymer for PSCs application for the first time. By conjugated aromatic ring with flourene unit, N-(aryl) 9H-fluoren-9-imine showed more planar conformation and electron donating ability. Based on N-(aryl) 9H-fluoren-9-imine with different substituents and BTzQx the narrow bandgap copolymers, exhibited an ideal bandgap of 1.55 eV. Primary device tests delivered a best PCE of 1.56% without any processing additives. This work has suggested that N-(aryl) 9H-fluoren-9-imine with different substituents unit could be a good choice of donor to construct fine-tuning physicochemical and photovoltaic properties of D-A polymers for PSCs.
Acknowledgments This work was financially supported by the National Natural Science Foundation of China (51202040, 21363006, 21563007 and 21201047), the Guangxi Natural Science Foundation (2015GXNSFBA139228).
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2016.04.009.
References [1] G. Yu, J. Gao, J.C. Hummelen, F. Wudl, A.J. Heeger, Science 270 (1995) 1789–1791. [2] Q. Gan, F.J. Bartoli, Z.H. Kafafi, Adv. Mater. 25 (2013) 2385–2396. [3] A.R.b.M. Yusoff, D. Kim, H.P. Kim, F.K. Shneider, W.J. da Silva, J. Jang, Energy Environ. Sci. 8 (2015) 303–316. [4] L. Dou, Y. Liu, Z. Hong, G. Li, Y. Yang, Chem. Rev. 115 (2015) 12633–12665. [5] I. Etxebarria, J. Ajuria, R. Pacios, Org. Electron. 19 (2015) 34–60. [6] G. Sauvé, R. Fernando, J. Phys. Chem. Lett. 6 (2015) 3770–3780. [7] C.C. Chen, W.H. Chang, K. Yoshimura, K. Ohya, J. You, J. Gao, Z. Hong, Y. Yang, Adv. Mater. 26 (2014) 5670–5677. [8] W. Yue, T.T. Larsen-Olsen, X. Hu, M. Shi, H. Chen, M. Hinge, et al., J. Mater. Chem. A 1 (2013) 1785–1793. [9] Y. Zhang, D. Deng, K. Lu, J. Zhang, B. Xia, Y. Zhao, et al., Adv. Mater. 27 (2015) 1071–1076. [10] B. Fu, C.-Y. Wang, B.D. Rose, Y. Jiang, M. Chang, P.-H. Chu, et al., Chem. Mater. 27 (2015) 2928–2937. [11] J. Zou, C.-Z. Li, C.-Y. Chang, H.-L. Yip, A.K.Y. Jen, Adv. Mater. 26 (2014) 3618–3623. [12] J. Hai, Y. Li, L. Yin, E. Zhu, L. Bian, W. Yu, et al., Polym. Chem. 5 (2014) 1163–1172. [13] J. Hai, B. Zhao, F. Zhang, C.-X. Sheng, L. Yin, Y. Li, et al., Polymer 54 (2013) 4930–4939. [14] J. Hai, B. Zhao, E. Zhu, L. Bian, H. Wu, W. Tang, Macromol. Chem. Phys. 214 (2013) 2473–2479. [15] J.D. Azoulay, Z.A. Koretz, B.M. Wong, G.C. Bazan, Macromolecules 46 (2013) 1337–1342. [16] C. Du, C. Li, W. Li, X. Chen, Z. Bo, C. Veit, et al., Macromolecules 44 (2011) 7617–7624. [17] W. Tang, L. Ke, L. Tan, T. Lin, T. Kietzke, Z.-K. Chen, Macromolecules 40 (2007) 6164–6171. [18] L. Bian, E. Zhu, J. Tang, W. Tang, F. Zhang, Prog. Polym. Sci. 37 (2012) 1292–1331. [19] Y. Huang, E.J. Kramer, A.J. Heeger, G.C. Bazan, Chem. Rev. 114 (2014) 7006–7043.