Chemical Analysis of the Interface in Bulk-Heterojunction Solar Cells by X-ray Photoelectron Spectroscopy Depth Profiling

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• 作者：Yan BusbyEmil J. W. List-Kratochvil ; Jean-Jacques Pireaux
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2017
• 出版时间：February 1, 2017
• 年：2017
• 卷：9
• 期：4
• 页码：3842-3848
• 全文大小：498K
• ISSN：1944-8252

文摘

Despite the wide use of blends combining an organic p-type polymer and molecular fullerene-based electron acceptor, the proper characterization of such bulk heterojunction materials is still challenging. To highlight structure-to-function relations and improve the device performance, advanced tools and strategies need to be developed to characterize composition and interfaces with sufficient accuracy. In this work, high-resolution X-ray photoelectron spectroscopy (XPS) is combined with very low energy argon ion beam sputtering to perform a nondestructive depth profile chemical analysis on full Al/P3HT:PCBM/PEDOT:PSS/ITO (P3HT, poly(3-hexylthiophene); PCBM, [6,6]-phenyl-C₆₁-butyric acid methyl ester; PEDOT, poly(3,4-ethylenedioxythiophene; PSS, polystyrenesulfonate; ITO, indium tin oxide) bulk-heterojunction solar cell device stacks. Key information, such as P3HT and PCBM composition profiles and Al-PCBM chemical bonding, are deduced in this basic device structure. The interface chemical analysis allows us to evidence, with unprecedented accuracy, the inhomogeneous distribution of PCBM, characterized by a strong segregation toward the top metal electrode. The chemical analysis high-resolution spectra allows us to reconstruct P3HT/PCBM ratio through the active layer depth and correlate with the device deposition protocol and performance. Results evidence an inhomogeneous P3HT/PCBM ratio and poorly controllable PCBM migration, which possibly explains the limited light-to-power conversion efficiency in this basic device structure. The work illustrates the high potential of XPS depth profile analysis for studying such organic/inorganic device stacks.