(709d) Designing Core/Shell Metal Organic Framework/Polymer Films As Scalable Barrier Layers for Enhanced Protection on Photovoltaics

Preventing module deterioration due to environmental stressors including moisture, mechanical stress, temperature and solar irradiation is critical in wide-ranging packaging applications, especially for the coatings used to ensure the life span and reliability of Photovoltaics cells. A simple, scalable, and cheap hybrid barrier layer system has been built based on Metal Organic Framework (MOF)/Cyclic Olefin Copolymer (COC) films which simultaneously achieved high light transmittance and mechanical stability, all while maintaining limited permeability of the reactive species into the device.

We previously developed highly transparent hybrid films based on a water-scavenging MOF and a commercial hydrophobic polymer COC fabricated by doctor blading, a commonly used industry method. Incorporating the hygroscopic MOF desiccants (a hydrophilic MOF capped with oleic acid for retaining an organic solubility) into the COC leads to a 10-fold decrease in WVTR, while maintaining an outstanding transparency over most of the solar spectrum.¹

In order to further optimize this successful system using MOF/COC films as barrier layers, we adapted a simple chemical functionalization method and achieved hygroscopic core/shell MOF nanoparticles providing a uniquely robust high-performance system at low cost. Besides using oleic acid for surface functionalization of MOF in the COC/MOF film, we adapted a layer-by-layer method to coat the MOF with ZIF-8 (hydrophobic MOF with smaller pore size). This ZIF acts as hydrophobic barrier, while also enhancing the compatibility with any hydrophobic polymers. This approach allows the MOF core to maintain its water-scavenging property and gain more stability by the shell protection. Controlling shell thickness and coverage area allows us to optimize design of the barrier layers and better understand the diffusion process. SEM, FTIR, TGA and XRD has been used for understanding the core/shell structures and compatibility between polymers and MOFs in the films. Small angle X-ray scattering (SAXS) has been used to investigate the nanocomposite morphology-moisture barrier relationship, which will further allow determination of the nanoparticle-nanoparticle spacing, nanoparticle size and copolymer lamella spacing and extent of multilayer order. These morphology studies will show how water is absorbed into the nanocomposite, and this understanding will allow design of more optimal copolymer-nanoparticle composites.

1. Youn Jue Bae, Eun Seon Cho, Fen Qiu, Daniel T. Sun, Teresa E. Williams, Jeffrey J. Urban, Wendy L. Queen “Transparent Metal-Organic Framework/Polymer Films as Water Vapor Barriers” ACS Appl. Mater. Interfaces 2016, 8, 10098-10103