Department of Chemistry, University of Washington, Seattle, Washington 98195, USA.
Acc Chem Res. 2010 May 18;43(5):612-20. doi: 10.1021/ar900231q.
The use of organic photovoltaics (OPVs) could reduce production costs for solar cells because these materials are solution processable and can be manufactured by roll-to-roll printing. The nanoscale texture, or film morphology, of the donor/acceptor blends used in most OPVs is a critical variable that can dominate both the performance of new materials being optimized in the lab and efforts to move from laboratory-scale to factory-scale production. Although efficiencies of organic solar cells have improved significantly in recent years, progress in morphology optimization still occurs largely by trial and error, in part because much of our basic understanding of how nanoscale morphology affects the optoelectronic properties of these heterogeneous organic semiconductor films has to be inferred indirectly from macroscopic measurements. In this Account, we review the importance of nanoscale morphology in organic semiconductors and the use of electrical scanning probe microscopy techniques to directly probe the local optoelectronic properties of OPV devices. We have observed local heterogeneity of electronic properties and performance in a wide range of systems, including model polymer-fullerene blends such as poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM), newer polyfluorene copolymer-PCBM blends, and even all polymer donor-acceptor blends. The observed heterogeneity in local photocurrent poses important questions, chiefly what information is contained and what is lost when using average values obtained from conventional measurements on macroscopic devices and bulk samples? We show that in many cases OPVs are best thought of as a collection of nanoscopic photodiodes connected in parallel, each with their own morphological and therefore electronic and optical properties. This local heterogeneity forces us to carefully consider the adequacy of describing OPVs solely by "average" properties such as the bulk carrier mobility. Characterizing this local heterogeneity in the morphology of an OPV and the consequent variations in local performance is vital to understanding OPV operation.
有机光伏（OPV）的使用可以降低太阳能电池的生产成本，因为这些材料可溶液处理，并可通过卷对卷印刷制造。在大多数 OPV 中使用的给体/受体共混物的纳米级纹理或薄膜形态是一个关键变量，它可以主导正在实验室中优化的新材料的性能以及从实验室规模向工厂规模生产过渡的努力。尽管近年来有机太阳能电池的效率有了显著提高，但形态优化的进展在很大程度上仍然是通过反复试验进行的，部分原因是我们对纳米形态如何影响这些异质有机半导体薄膜的光电性能的基本理解在很大程度上必须从宏观测量中推断出来。在本说明中，我们回顾了纳米形态在有机半导体中的重要性以及使用电子扫描探针显微镜技术直接探测 OPV 器件的局部光电特性。我们已经观察到了广泛的系统中电子性能和性能的局部异质性，包括模型聚合物-富勒烯共混物，如聚（3-己基噻吩）（P3HT）和[6,6]-苯基-C（61）-丁酸甲酯（PCBM），较新的聚芴共聚物-PCBM 共混物，甚至是全聚合物给体-受体共混物。局部光电流的观察到的异质性提出了重要的问题，主要是在使用从宏观器件和体样品的常规测量获得的平均值时包含了什么信息以及丢失了什么信息？我们表明，在许多情况下，最好将 OPV 视为彼此并联的纳米级光电二极管的集合，每个光电二极管都具有自己的形态，因此具有自己的电子和光学特性。这种局部异质性迫使我们仔细考虑仅通过“平均”特性（例如体载流子迁移率）来描述 OPV 是否充分。对 OPV 的形态的这种局部异质性进行表征以及由此导致的局部性能变化对于理解 OPV 的运行至关重要。
