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 layerand 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 (λ_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.

中文翻译：

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边缘功能化石墨烯量子点作为厚度不敏感的聚合物太阳能电池阴极夹层

对于大面积聚合物太阳能电池（PSC），厚度不敏感的阴极夹层（CIL）是必不可少的，在这种情况下，厚度变化是不可避免的。这些CIL材料通常基于n型共轭聚合物/分子主链，在可见/近红外（NIR）区域显示出强大的光吸收能力。这会干扰有源层吸收的阳光并降低器件效率。在这项研究中，我们开发了在边缘用碘化铵（GQD-NI）功能化的石墨烯量子点，作为具有高光学透明性的厚度不敏感的CIL。GQD-NI的外围碘化铵基团与阴极形成了所需的界面偶极子，从而降低了功函。GQD-NI的石墨烯基面的横向尺寸为ca。3 nm表现出3.56×10的良好电导率^-6 S·厘米^-1和在可见光/近红外区域具有高透明度（λ_最大^绝对= 228纳米）。此外，GQD-NI易溶于极性有机溶剂（例如甲醇），从而可以通过正交溶剂加工制造多层器件。结果，以GQD-NI作为CIL的PSC装置的功率转换效率（PCE）为7.49％，远高于没有CIL的装置（PCE = 5.38％）或以钙为CIL的装置的功率转换效率。 （PCE = 6.72％）。此外，GQD-NI的PSC器件性能对2-22 nm范围内的GQD-NI层厚度不敏感。这些结果表明，GQD-NI是在大面积印刷的PSC中用作CIL的非常有前途的材料。