National Physical Laboratory, Teddington, Middlesex, UK TW11 0LW.
Department of Physics, Imperial College London, London, UK SW7 2AZ.
Nanoscale. 2017 Feb 23;9(8):2723-2731. doi: 10.1039/c6nr09057e.
Novel optoelectronic devices rely on complex nanomaterial systems where the nanoscale morphology and local chemical composition are critical to performance. However, the lack of analytical techniques that can directly probe these structure-property relationships at the nanoscale presents a major obstacle to device development. In this work, we present a novel method for non-destructive, simultaneous mapping of the morphology, chemical composition and photoelectrical properties with <20 nm spatial resolution by combining plasmonic optical signal enhancement with electrical-mode scanning probe microscopy. We demonstrate that this combined approach offers subsurface sensitivity that can be exploited to provide molecular information with a nanoscale resolution in all three spatial dimensions. By applying the technique to an organic solar cell device, we show that the inferred surface and subsurface composition distribution correlates strongly with the local photocurrent generation and explains macroscopic device performance. For instance, the direct measurement of fullerene phase purity can distinguish between high purity aggregates that lead to poor performance and lower purity aggregates (fullerene intercalated with polymer) that result in strong photocurrent generation and collection. We show that the reliable determination of the structure-property relationship at the nanoscale can remove ambiguity from macroscopic device data and support the identification of the best routes for device optimisation. The multi-parameter measurement approach demonstrated herein is expected to play a significant role in guiding the rational design of nanomaterial-based optoelectronic devices, by opening a new realm of possibilities for advanced investigation via the combination of nanoscale optical spectroscopy with a whole range of scanning probe microscopy modes.
新型光电设备依赖于复杂的纳米材料系统，其中纳米级形态和局部化学成分对性能至关重要。然而，缺乏能够直接在纳米尺度上探测这些结构-性能关系的分析技术，这是器件开发的主要障碍。在这项工作中，我们提出了一种新的方法，通过将等离子体光学信号增强与电模式扫描探针显微镜相结合，实现了对形貌、化学成分和光电性能的非破坏性、同时映射，空间分辨率小于 20nm。我们证明，这种组合方法具有亚表面灵敏度，可以利用它在所有三个空间维度上以纳米级分辨率提供分子信息。通过将该技术应用于有机太阳能电池器件，我们表明推断的表面和亚表面组成分布与局部光电流产生强烈相关，并解释了宏观器件性能。例如，富勒烯相纯度的直接测量可以区分导致性能不佳的高纯度聚集体和导致强光电流产生和收集的低纯度聚集体（聚合物插层富勒烯）。我们表明，在纳米尺度上可靠地确定结构-性能关系可以消除宏观器件数据中的歧义，并支持确定器件优化的最佳途径。本文演示的多参数测量方法有望通过将纳米级光学光谱与各种扫描探针显微镜模式相结合，为先进的研究开辟新的可能性，从而在指导基于纳米材料的光电设备的合理设计方面发挥重要作用。
