Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology , Guangzhou 510640, PR China.
J Am Chem Soc. 2016 Feb 17;138(6):2004-13. doi: 10.1021/jacs.5b12664. Epub 2016 Feb 4.
With the demonstration of small-area, single-junction polymer solar cells (PSCs) with power conversion efficiencies (PCEs) over the 10% performance milestone, the manufacturing of high-performance large-area PSC modules is becoming the most critical issue for commercial applications. However, materials and processes that are optimized for fabricating small-area devices may not be applicable for the production of high-performance large-area PSC modules. One of the challenges is to develop new conductive interfacial materials that can be easily processed with a wide range of thicknesses without significantly affecting the performance of the PSCs. Toward this goal, we report two novel naphthalene diimide-based, self-doped, n-type water/alcohol-soluble conjugated polymers (WSCPs) that can be processed with a broad thickness range of 5 to 100 nm as efficient electron transporting layers (ETLs) for high-performance PSCs. Space charge limited current and electron spin resonance spectroscopy studies confirm that the presence of amine or ammonium bromide groups on the side chains of the WSCP can n-dope PC71BM at the bulk heterojunction (BHJ)/ETL interface, which improves the electron extraction properties at the cathode. In addition, both amino functional groups can induce self-doping to the WSCPs, although by different doping mechanisms, which leads to highly conductive ETLs with reduced ohmic loss for electron transport and extraction. Ultimately, PSCs based on the self-doped WSCP ETLs exhibit significantly improved device performance, yielding PCEs as high as 9.7% and 10.11% for PTB7-Th/PC71BM and PffBT4T-2OD/PC71BM systems, respectively. More importantly, with PffBT4T-2OD/PC71BM BHJ as an active layer, a prominent PCE of over 8% was achieved even when a thick ETL of 100 nm was used. To the best of our knowledge, this is the highest efficiency demonstrated for PSCs with a thick interlayer and light-harvesting layer, which are important criteria for eventually making organic photovoltaic modules based on roll-to-roll coating processes.
随着小面积、单结聚合物太阳能电池（PSCs）的演示，其功率转换效率（PCE）超过 10%的性能里程碑，制造高性能大面积 PSC 模块成为商业应用的最关键问题。然而，为制造小面积器件而优化的材料和工艺可能不适用于高性能大面积 PSC 模块的生产。其中一个挑战是开发新的导电界面材料，这些材料可以在很宽的厚度范围内进行处理，而不会显著影响 PSCs 的性能。为实现这一目标，我们报告了两种新型基于萘二酰亚胺的、自掺杂的、n 型水/醇溶性共轭聚合物（WSCP），它们可以在 5 至 100nm 的宽厚度范围内进行处理，作为高效电子传输层（ETL）用于高性能 PSCs。空间电荷限制电流和电子自旋共振光谱研究证实，WSCP 侧链上的胺或溴化铵基团的存在可以在本体异质结（BHJ）/ETL 界面处对 PC71BM 进行 n 掺杂，从而改善了对阴极的电子提取性能。此外，两个氨基官能团都可以诱导 WSCP 自掺杂，尽管掺杂机制不同，这导致了具有高导电性的 ETL，从而降低了电子传输和提取的欧姆损耗。最终，基于自掺杂 WSCP ETL 的 PSCs 表现出显著改善的器件性能，PTB7-Th/PC71BM 和 PffBT4T-2OD/PC71BM 系统的 PCE 分别高达 9.7%和 10.11%。更重要的是，当使用 100nm 厚的 ETL 时，以 PffBT4T-2OD/PC71BM BHJ 为活性层，仍实现了超过 8%的突出 PCE。据我们所知，这是使用厚层和光收集层的 PSCs 中展示的最高效率，这是最终基于卷对卷涂层工艺制造有机光伏模块的重要标准。
