Nano Research

, Volume 11, Issue 8, pp 4293–4301 | Cite as

Edge-functionalized graphene quantum dots as a thickness-insensitive cathode interlayer for polymer solar cells

  • Han Xu
  • Lu Zhang
  • Zicheng Ding
  • Junli HuEmail author
  • Jun LiuEmail author
  • Yichun LiuEmail author
Research Article


A thickness-insensitive cathode interlayer (CIL) is necessary for large-area polymer solar cells (PSCs), in which thickness variation is unavoidable. These CIL materials are typically based on n-type conjugated polymer/molecule backbones, which show strong light absorption in the visible/near-infrared (NIR) region. This interferes with the sunlight absorption by the active layer and deteriorates device efficiency. In this study, we developed graphene quantum dots functionalized with ammonium iodide (GQD-NI) at the edge as a thickness-insensitive CIL with high optical transparency. The peripheral ammonium iodide groups of GQD-NI formed the desired interfacial dipole with the cathode to decrease the work function. The graphene basal planes of GQD-NI with a lateral size of ca. 3 nm demonstrated a good conductivity of 3.56 × 10–6 S·cm–1 and high transparency in the visible/NIR region (λmaxabs = 228 nm). Moreover, GQD-NI was readily soluble in polar organic solvents, e.g., methanol, which enabled multilayer device fabrication with orthogonal solvent processing. As a result, the PSC device with GQD-NI as the CIL exhibited a power conversion efficiency (PCE) of 7.49%, which was much higher than that of the device without the CIL (PCE = 5.38%) or with calcium as the CIL (PCE = 6.72%). Moreover, the PSC device performance of GQD-NI was insensitive to the GQD-NI layer thickness in the range of 2–22 nm. These results indicate that GQD-NI is a very promising material for application as a CIL in large-area printed PSCs.


graphene quantum dots ammonium edge-functionalization cathode interlayer polymer solar cells 


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The authors are grateful for the financial supports by the National Basic Research Program of China (No. 2014CB643504), the National Natural Science Foundation of China (Nos. 21625403 and 51503198), the 111 project (No. B13013), Jilin Scientific and Technological Development Program (No. 20170519003JH), Northeast Normal University (No. 130028724), and State Key Laboratory of Luminescence and Applications (No. SKLA-2016-02).

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Edge-functionalized graphene quantum dots as a thickness-insensitive cathode interlayer for polymer solar cells


  1. [1]
    Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Polymer photovoltaic cells: Enhanced efficiencies via a network of internal donor-acceptor heterojunctions. Science 1995, 270, 1789–1791.CrossRefGoogle Scholar
  2. [2]
    Li, G.; Zhu, R.; Yang, Y. Polymer solar cells. Nat. Photonics 2012, 6, 153–161.CrossRefGoogle Scholar
  3. [3]
    Kang, H.; Kim, G.; Kim, J.; Kwon, S.; Kim, H.; Lee, K. Bulk-heterojunction organic solar cells: Five core technologiesfor their commercialization. Adv. Mater. 2016, 28, 7821–7861.CrossRefGoogle Scholar
  4. [4]
    Zhao, R. Y.; Dou, C. D.; Liu, J.; Wang, L. X. An alternating polymer of two building blocks based on B←N unit: Non-fullerene acceptor for organic photovoltaics. Chinese J. Polym. Sci. 2017, 35, 198–206.CrossRefGoogle Scholar
  5. [5]
    Dou, C. D.; Liu, J.; Wang, L. X. Conjugated polymers containing B←N unit as electron acceptors for all-polymer solar cells. Sci. China Chem. 2017, 60, 450–459.CrossRefGoogle Scholar
  6. [6]
    Chueh, C. C.; Li, C.-Z.; Jen, A. K.-Y. Recent progress and perspective in solution-processed interfacial materials for efficient and stable polymer and organometal perovskite solar cells. Energy Environ. Sci. 2015, 8, 1160–1189.Google Scholar
  7. [7]
    Xu, B. W.; Zheng, Z.; Zhao, K.; Hou, J. H. A bifunctional interlayer material for modifying both the anode and cathode in highly efficient polymer solar cells. Adv. Mater. 2016, 28, 434–439.CrossRefGoogle Scholar
  8. [8]
    Nian, L.; Zhang, W. Q.; Zhu, N.; Liu, L. L.; Xie, Z. Q.; Wu, H. B.; Würthner, F.; Ma, Y. G. Photoconductive cathode interlayer for highly efficient inverted polymer solar cells. J. Am. Chem. Soc. 2015, 137, 6995–6998.CrossRefGoogle Scholar
  9. [9]
    Sun, Y. M.; Takacs, C. J.; Cowan, S. R.; Seo, J. H.; Gong, X.; Roy, A.; Heeger, A. J. Efficient, air-stable bulk heterojunction polymer solar cells using MoOx as the anode interfacial layer. Adv. Mater. 2011, 23, 2226–2230.CrossRefGoogle Scholar
  10. [10]
    Tan, Z. A,; Zhang, W. Q.; Zhang, Z. G.; Qian, D. P.; Huang, Y.; Hou, J. H.; Li, Y. F. High-performance inverted polymer solar cells with solution-processed titanium chelate as electron-collecting layer on ITO electrode. Adv. Mater. 2012, 24, 1476–1481.CrossRefGoogle Scholar
  11. [11]
    Shrotriya, V.; Li, G.; Yao, Y.; Chu, C. W.; Yang, Y. Transition metal oxides as the buffer layer for polymer photovoltaic cells. Appl. Phys. Lett. 2006, 88, 073508.CrossRefGoogle Scholar
  12. [12]
    Duan, C. H.; Zhang, K.; Zhong, C. M.; Huang, F.; Cao, Y. Recent advances in water/alcohol-soluble π-conjugated materials: New materials and growing applications in solar cells. Chem. Soc. Rev. 2013, 42, 9071–9104.CrossRefGoogle Scholar
  13. [13]
    He, Z. C.; Zhong, C. M.; Su, S. J.; Xu, M.; Wu, H. B.; Cao, Y. Enhanced power-conversion efficiency in polymer solar cells using an inverted device structure. Nat. Photonics 2012, 6, 591–595.CrossRefGoogle Scholar
  14. [14]
    Wang, J.; Lin, K.; Zhang, K.; Jiang, X. F.; Mahmood, K.; Ying, L.; Huang, F.; Cao, Y. Crosslinkable amino-functionalized conjugated polymer as cathode interlayer for efficient inverted polymer solar cells. Adv. Energy Mater. 2016, 6, 1502563.CrossRefGoogle Scholar
  15. [15]
    Min, C.; Shi, C. S.; Zhang, W. J.; Jiu, T. G.; Chen, J. S.; Ma, D. G.; Fang, J. F. A small-molecule zwitterionic electrolyte without a π-delocalized unit as a charge-injection layer for high-performance PLEDs. Angew. Chem., Int. Ed. 2013, 52, 3417–3420.CrossRefGoogle Scholar
  16. [16]
    Liao, S. H.; Li, Y. L.; Jen, T. H.; Cheng, Y. S.; Chen, S. A. Multiple functionalities of polyfluorene grafted with metal ion-intercalated crown ether as an electron transport layer for bulk-heterojunction polymer solar cells: Optical interference, hole blocking, interfacial dipole, and electron conduction. J. Am. Chem. Soc. 2012, 134, 14271–14274.CrossRefGoogle Scholar
  17. [17]
    Seo, J. H.; Gutacker, A.; Sun, Y. M.; Wu, H. B.; Huang, F.; Cao, Y.; Scherf, U.; Heeger, A. J.; Bazan, G. C. Improved high-efficiency organic solar cells via incorporation of a conjugated polyelectrolyte interlayer. J. Am. Chem. Soc. 2011, 133, 8416–8419.CrossRefGoogle Scholar
  18. [18]
    Kang, R.; Oh, S. H.; Kim, D. Y. Influence of the ionic functionalities of polyfluorene derivatives as a cathode interfacial layer on inverted polymer solar cells. ACS Appl. Mater. Interfaces 2014, 6, 6227–6236.CrossRefGoogle Scholar
  19. [19]
    Hoven, C. V.; Garcia, A.; Bazan, G. C.; Nguyen, T.-Q. Recent applications of conjugated polyelectrolytes in optoelectronic devices. Adv. Mater. 2008, 20, 3793–3810.CrossRefGoogle Scholar
  20. [20]
    Huang, F.; Wu, H. B.; Wang, D. L.; Yang, W.; Cao, Y. Novel electroluminescent conjugated polyelectrolytes based on polyfluorene. Chem. Mater. 2004, 16, 708–716.CrossRefGoogle Scholar
  21. [21]
    Zhou, Y. H.; Fuentes-Hernandez, C.; Shim, J.; Meyer, J.; Giordano, A. J.; Li, H.; Winget, P.; Papadopoulos, T.; Cheun, H.; Kim, J. et al. A universal method to produce low-work function electrodes for organic electronics. Science 2012, 336, 327–332.CrossRefGoogle Scholar
  22. [22]
    Yao, K.; Salvador, M.; Chueh, C.-C.; Xin, X.-K.; Xu, Y.-X.; de Quilettes, D. W.; Hu, T.; Chen, Y. W.; Ginger, D. S.; Jen, A. K.-Y. A general route to enhance polymer solar cell performance using plasmonic nanoprisms. Adv. Energy Mater. 2014, 4, 1400206.Google Scholar
  23. [23]
    Liu, S. J.; Zhang, K.; Lu, J. M.; Zhang, J.; Yip, H. L.; Huang, F.; Cao, Y. High-efficiency polymer solar cells via the incorporation of an amino-functionalized conjugated metallopolymer as a cathode interlayer. J. Am. Chem. Soc. 2013, 135, 15326–15329.CrossRefGoogle Scholar
  24. [24]
    Wu, Z. H.; Sun, C.; Dong, S.; Jiang, X. F.; Wu, S. P.; Wu, H. B.; Yip, H. L.; Huang, F.; Cao, Y. n-Type water/alcohol-soluble naphthalene diimide-based conjugated polymers for high-performance polymer solar cells. J. Am. Chem. Soc. 2016, 138, 2004–2013.CrossRefGoogle Scholar
  25. [25]
    Liu, Y.; Page, Z. A.; Russell, T. P.; Emrick, T. Finely tuned polymer interlayers enhance solar cell efficiency. Angew. Chem., Int. Ed. 2015, 54, 11485–11489.CrossRefGoogle Scholar
  26. [26]
    Page, Z. A.; Liu, Y.; Duzhko, V. V.; Russell, T. P.; Emrick, T. Fulleropyrrolidine interlayers: Tailoring electrodes to raise organic solar cell efficiency. Science 2014, 346, 441–444.CrossRefGoogle Scholar
  27. [27]
    Li, S. S.; Lei, M.; Lv, M. L.; Watkins, S. E.; Tan, Z. A.; Zhu, J.; Hou, J. H.; Chen, X. W.; Li, Y. F. [6,6]-phenyl-C61-butyric acid dimethylamino ester as a cathode buffer layer for high- performance polymer solar cells. Adv. Energy Mater. 2013, 3, 1569–1574.CrossRefGoogle Scholar
  28. [28]
    Zhang, Z.-G.; Qi, B. Y.; Jin, Z. W.; Chi, D.; Qi, Z. F.; Li, Y. F.; Wang, J. Z. Perylene diimides: A thickness-insensitive cathode interlayer for high performance polymer solar cells. Energy Environ. Sci. 2014, 7, 1966–1973.CrossRefGoogle Scholar
  29. [29]
    Hu, L.; Wu, F. Y.; Li, C. Q.; Hu, A. F.; Hu, X. T.; Zhang, Y.; Chen, L.; Chen, Y. W. Alcohol-soluble n-type conjugated polyelectrolyte as electron transport layer for polymer solar cells. Macromolecules 2015, 48, 5578–5586.CrossRefGoogle Scholar
  30. [30]
    Liu, J.; Durstock, M.; Dai, L. M. Graphene oxide derivatives as hole- and electron-extraction layers for high-performance polymer solar cells. Energy Environ. Sci. 2014, 7, 1297–1306.CrossRefGoogle Scholar
  31. [31]
    Liu, J.; Xue, Y. H.; Gao, Y. X.; Yu, D. S.; Durstock, M.; Dai, L. M. Hole and electron extraction layers based on graphene oxide derivatives for high-performance bulk heterojunction solar cells. Adv. Mater. 2012, 24, 2228–2233.CrossRefGoogle Scholar
  32. [32]
    Liu, J.; Kim, G.-H.; Xue, Y. H.; Kim, J. Y.; Baek, J.-B.; Durstock, M.; Dai, L. M. Graphene oxide nanoribbon as hole extraction layer to enhance efficiency and stability of polymer solar cells. Adv. Mater. 2014, 26, 786–790.CrossRefGoogle Scholar
  33. [33]
    Li, S. S.; Tu, K. H.; Lin, C. C.; Chen, C. W.; Chhowalla, M. Solution-processable graphene oxide as an efficient hole transport layer in polymer solar cells. ACS Nano 2010, 4, 3169–3174.CrossRefGoogle Scholar
  34. [34]
    Yun, J. M.; Yeo, J. S.; Kim, J.; Jeong, H. G.; Kim, D. Y.; Noh, Y. J.; Kim, S. S.; Ku, B. C.; Na, S. I. Solution-processable reduced graphene oxide as a novel alternative to PEDOT:PSS hole transport layers for highly efficient and stable polymer solar cells. Adv. Mater. 2011, 23, 4923–4928.CrossRefGoogle Scholar
  35. [35]
    Yeo, J.-S.; Yun, J.-M.; Jung, Y.-S.; Kim, D.-Y.; Noh, Y.-J.; Kim, S.-S.; Na, S.-I. Sulfonic acid-functionalized, reduced graphene oxide as an advanced interfacial material leading to donor polymer-independent high-performance polymer solar cells. J. Mater. Chem. A 2014, 2, 292–298.CrossRefGoogle Scholar
  36. [36]
    Yang, D.; Zhou, L. Y.; Chen, L. C.; Zhao, B.; Zhang, J.; Li, C. Chemically modified graphene oxides as a hole transport layer in organic solar cells. Chem. Commun. 2012, 48, 8078–8080.CrossRefGoogle Scholar
  37. [37]
    Yang, D.; Zhou, L. Y.; Yu, W.; Zhang, J.; Li, C. Work-function- tunable chlorinated graphene oxide as an anode interface layer in high-efficiency polymer solar cells. Adv. Energy Mater. 2014, 4, 1400591.CrossRefGoogle Scholar
  38. [38]
    Konios, D.; Kakavelakis, G.; Petridis, C.; Savva, K.; Stratakisab, E.; Kymakis, E. Highly efficient organic photovoltaic devices utilizing work-function tuned graphene oxide derivatives as the anode and cathode charge extraction layers. J. Mater. Chem. A 2016, 4, 1612–1623.CrossRefGoogle Scholar
  39. [39]
    Kakavelakis, G.; Konios, D.; Stratakis, E.; Kymakis, E. Enhancement of the efficiency and stability of organic photovoltaic devices via the addition of a lithium-neutralized graphene oxide electron-transporting layer. Chem. Mater. 2014, 26, 5988–5993.CrossRefGoogle Scholar
  40. [40]
    Hu, A. F.; Wang, Q. X.; Chen, L.; Hu, X. T.; Zhang, Y.; Wu, Y. F.; Chen, Y. C. In situ formation of ZnO in graphene: A facile way to produce a smooth and highly conductive electron transport layer for polymer solar cells. ACS Appl. Mater. Interfaces 2015, 7, 16078–16085.CrossRefGoogle Scholar
  41. [41]
    Kim, J.; Lee, H.; Lee, S. J.; da Silva, W. J.; bin Mohd Yusoffa, A. R.; Jang, J. Graphene oxide grafted polyethylenimine electron transport materials for highly efficient organic devices. J. Mater. Chem. A 2015, 3, 22035–22042.CrossRefGoogle Scholar
  42. [42]
    Chao, Y.-H.; Wu, J.-S.; Wu, C.-E.; Jheng, J.-F.; Wang, C.-L.; Hsu, C.-S. Solution-processed (graphene oxide)–(d0 transition metal oxide) composite anodic buffer layers toward high-performance and durable inverted polymer solar cells. Adv. Energy Mater. 2013, 3, 1279–1285.CrossRefGoogle Scholar
  43. [43]
    Li, M. M.; Ni, W.; Kan, B.; Wan, X. J.; Zhang, L.; Zhang, Q.; Long, G. K.; Zuo, Y.; Chen, Y. S. Graphene quantum dots as the hole transport layer material for high-performance organic solar cells. Phys. Chem. Chem. Phys. 2013, 15, 18973–18978.CrossRefGoogle Scholar
  44. [44]
    Ding, Z. C.; Hao, Z.; Meng, B.; Xie, Z. Y.; Liu, J.; Dai, L. M. Few-layered graphene quantum dots as efficient hole-extraction layer for high-performance polymer solar cells. Nano Energy 2015, 15, 186–192.CrossRefGoogle Scholar
  45. [45]
    Ding, Z. C.; Miao, Z. S.; Xie, Z. Y.; Liu, J. Functionalized graphene quantum dots as a novel cathode interlayer of polymer solar cells. J. Mater. Chem. A 2016, 4, 2413–2418.CrossRefGoogle Scholar
  46. [46]
    Yang, H. B.; Dong, Y. Q.; Wang, X. Z.; Khoo, S. Y.; Liu, B. Cesium carbonate functionalized graphene quantum dots as stable electron-selective layer for improvement of inverted polymer solar cells. ACS Appl. Mater. Interfaces 2014, 6, 1092–1099.CrossRefGoogle Scholar
  47. [47]
    Choi, H.-J.; Jung, S.-M.; Seo, J.-M.; Chang, D. W.; Dai, L. M.; Baek, J.-B. Graphene for energy conversion and storage in fuel cells and supercapacitors. Nano Energy 2012, 1, 534–551.CrossRefGoogle Scholar
  48. [48]
    Shivananju, B. N.; Yu, W. Z.; Liu, Y.; Zhang, Y. P.; Lin, B.; Li, S. J.; Bao, Q. L. The roadmap of graphene-based optical biochemical sensors. Adv. Funct. Mater. 2017, 27, 1603918.CrossRefGoogle Scholar
  49. [49]
    Tetsuka, H.; Nagoya, A.; Fukusumi, T.; Matsui, T. Molecularly designed, nitrogen-functionalized graphene quantum dots for optoelectronic devices. Adv. Mater. 2016, 28, 4632–4638.CrossRefGoogle Scholar
  50. [50]
    Meng, B.; Fu, Y. Y.; Xie, Z. Y.; Liu, J.; Wang, L. X. Phosphonate-functionalized donor polymer as an underlying interlayer to improve active layer morphology in polymer solar cells. Macromolecules 2014, 47, 6246–6251.CrossRefGoogle Scholar
  51. [51]
    Li, C. Z.; Chueh, C. C.; Ding, F. Z.; Yip, H.-L.; Liang, P.-W.; Li, X. S.; Jen, A. K.-Y. Doping of fullerenes via anion-induced electron transfer and its implication for surfactant facilitated high performance polymer solar cells. Adv. Mater. 2013, 25, 4425–4430.CrossRefGoogle Scholar

Copyright information

© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Key Laboratory of UV-Emitting Materials and Technology (Northeast Normal University)Ministry of EducationChangchunChina
  2. 2.State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied ChemistryChinese Academy of SciencesChangchunChina

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