Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
Nano Lett. 2012 Dec 12;12(12):6315-21. doi: 10.1021/nl303419n. Epub 2012 Dec 3.
Zinc oxide is a promising candidate as an interfacial layer (IFL) in inverted organic photovoltaic (OPV) cells due to the n-type semiconducting properties as well as chemical and environmental stability. Such ZnO layers collect electrons at the transparent electrode, typically indium tin oxide (ITO). However, the significant resistivity of ZnO IFLs and an energetic mismatch between the ZnO and the ITO layers hinder optimum charge collection. Here we report that inserting nanoscopic copper hexadecafluorophthalocyanine (F(16)CuPc) layers, as thin films or nanowires, between the ITO anode and the ZnO IFL increases OPV performance by enhancing interfacial electron transport. In inverted P3HT:PC(61)BM cells, insertion of F(16)CuPc nanowires increases the short circuit current density (J(sc)) versus cells with only ZnO layers, yielding an enhanced power conversion efficiency (PCE) of ∼3.6% vs ∼3.0% for a control without the nanowire layer. Similar effects are observed for inverted PTB7:PC(71)BM cells where the PCE is increased from 8.1% to 8.6%. X-ray scattering, optical, and electrical measurements indicate that the performance enhancement is ascribable to both favorable alignment of the nanowire π-π stacking axes parallel to the photocurrent flow and to the increased interfacial layer-active layer contact area. These findings identify a promising strategy to enhance inverted OPV performance by inserting anisotropic nanostructures with π-π stacking aligned in the photocurrent flow direction.
氧化锌作为一种有前途的界面层（IFL）材料，在倒置有机光伏（OPV）电池中得到了广泛的研究，这主要是因为其具有 n 型半导体特性以及化学和环境稳定性。这种氧化锌层在透明电极（通常是氧化铟锡（ITO））处收集电子。然而，氧化锌 IFL 的高电阻率和氧化锌与 ITO 层之间的能量不匹配阻碍了最佳电荷收集。在这里，我们报告称，在 ITO 阳极和 ZnO IFL 之间插入纳米尺度的铜六氟酞菁（F(16)CuPc）层（无论是薄膜还是纳米线），可以通过增强界面电子输运来提高 OPV 的性能。在倒置的 P3HT:PC(61)BM 电池中，插入 F(16)CuPc 纳米线会增加短路电流密度（J(sc)），与仅具有 ZnO 层的电池相比，其功率转换效率（PCE）从 3.0%提高到了 3.6%，而没有纳米线层的对照电池的 PCE 为 3.0%。在倒置的 PTB7:PC(71)BM 电池中也观察到了类似的效果，其中 PCE 从 8.1%提高到了 8.6%。X 射线散射、光学和电学测量表明，性能的提高归因于纳米线 π-π 堆叠轴与光电流流动方向平行的有利排列，以及界面层-活性层接触面积的增加。这些发现确定了一种通过插入具有与光电流流动方向平行的 π-π 堆叠排列的各向异性纳米结构来提高倒置 OPV 性能的有前途的策略。
