Journal
NANO RESEARCH
Volume 11, Issue 8, Pages 4293-4301Publisher
TSINGHUA UNIV PRESS
DOI: 10.1007/s12274-018-2015-y
Keywords
graphene quantum dots; ammonium; edge-functionalization; cathode interlayer; polymer solar cells
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Funding
- National Basic Research Program of China [2014CB643504]
- National Natural Science Foundation of China [21625403, 51503198]
- 111 project [B13013]
- Jilin Scientific and Technological Development Program [20170519003JH]
- Northeast Normal University [130028724]
- State Key Laboratory of Luminescence and Applications [SKLA-2016-02]
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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 x 10(-6) S.cm(-1) and high transparency in the visible/NIR region (lambda (max) (abs) = 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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