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Nano Research 2018, 11(8): 4293-4301 https://doi.org/10.1007/s12274-018-2015-y
Research Article | Issue | Published: 10 March 2018

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

Show Author's Information Han Xu1,2,§,  Lu Zhang2,§,  Zicheng Ding2,  Junli Hu1( ),  Jun Liu2( ),  Yichun Liu1( )
Key Laboratory of UV-Emitting Materials and Technology (Northeast Normal University)Ministry of EducationChangchun130024China
State Key Laboratory of Polymer Physics and ChemistryChangchun Institute of Applied ChemistryChinese Academy of SciencesChangchun130022China

§ Han Xu and Lu Zhang contributed equally to this work.

Keywords:
graphene quantum dots, ammonium, edge-functionalization, cathode interlayer, polymer solar cells
Cite this article:
Xu H, Zhang L, Ding Z, et al. Edge-functionalized graphene quantum dots as a thickness-insensitive cathode interlayer for polymer solar cells. Nano Research, 2018, 11(8): 4293-4301. https://doi.org/10.1007/s12274-018-2015-y
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Abstract Full text Electronic supplementary material About this 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.


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Electronic supplementary material
About this article

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

Show Author's information Han Xu1,2,§, Lu Zhang2,§, Zicheng Ding2, Junli Hu1( ), Jun Liu2( ), Yichun Liu1( )
Key Laboratory of UV-Emitting Materials and Technology (Northeast Normal University)Ministry of EducationChangchun130024China
State Key Laboratory of Polymer Physics and ChemistryChangchun Institute of Applied ChemistryChinese Academy of SciencesChangchun130022China

§ Han Xu and Lu Zhang contributed equally to this work.

Abstract

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.

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

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Publication history
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Acknowledgements

Publication history

Received: 22 October 2017
Revised: 01 February 2018
Accepted: 03 February 2018
Published: 10 March 2018
Issue date: August 2018

Copyright

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

Acknowledgements

Acknowledgements

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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