Adhesion and debonding kinetics in inverted polymer solar cells
- Organic photovoltaic (OPV) devices using materials compatible with flexible plastic substrates, have reached over 10 % power conversion efficiency, one of the critical milestones for market penetration. However, organic materials are often mechanically fragile compared to their inorganic counterparts, and devices containing these materials have a higher tendency for adhesive and cohesive failure. Using a thin-film adhesion technique that enables us to precisely measure the energy required to separate adjacent layers, weak interfaces in OPV devices were identified. For example, the interface of the P3HT:PCBM and PEDOT:PSS in a polymer solar cell with the inverted device architecture has an adhesive value of only ~1.5 to 2 J/m2. Such poor adhesion between adjacent thin-films can contribute to low processing yield and poor long-term reliability. Several strategies to improve the adhesion are proposed and quantified in this work, including chemical and thermal treatments. Pre and post electrode deposition thermal annealing can be used to tune interfacial and film parameters, such as interface chemistry, bonding and morphology to improve the adhesion. Post annealing effectively improved the adhesion at the P3HT:PCBM/PEDOT:PSS interface. Using near edge X-ray absorption fine structure (NEXAFS), we precisely quantified the interfacial composition and P3HT orientation at the delaminated surfaces and correlated the increase in adhesion to changes in the interfacial structure. The structural and chemical reorganizations are correlated with the glass transition and crystallization temperatures of the materials used in the structure and thus the conclusion can be generalized to other materials systems. Understanding the interlayer adhesion and developing strategies to improve the adhesion of OPV materials is essential to improve the overall mechanical integrity and yield general guidelines for the design and processing of reliable OPV devices. We also demonstrate how moisture and temperature accelerate debond propagation at mechanical stresses well below those required for critical failure. Understanding such debonding kinetics is critical for device reliability and lifetime. When environmental species are introduced, the bulk layers and other interfaces in the OPV structure become more susceptible to debonding. The cohesion of the PEDOT:PSS layer is significantly influenced by moisture along with temperature and mechanical loads. Elucidating the kinetic mechanisms using atomistic bond rupture models supports that decohesion is facilitated by a chemical reaction between water molecules from the environment and strained hydrogen bonds. This extensive series of quantitative analysis provides the impact of the different environmental species and most importantly their synergies, leading us to an in-depth understanding of the debonding mechanisms.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Dupont, Stéphanie Renee Christel
|Stanford University, Department of Materials Science and Engineering.
|Dauskardt, R. H. (Reinhold H.)
|Dauskardt, R. H. (Reinhold H.)
|Statement of responsibility
|Stéphanie Renee Christel Dupont.
|Submitted to the Department of Materials Science and Engineering.
|Thesis (Ph.D.)--Stanford University, 2014.
- © 2014 by Stephanie R. C. Dupont
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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