聚氨酯/石墨烯複合封裝材料之分散性，原位聚合特性與阻氣性質研究

Abstract

石墨烯納米片（GNS）具有不透水性、疏水性和高長寬比，因此添加石墨烯納米片（GNS）強化高分子材料有助於實現極低的水氣滲透率，進而成為具有潛力的電子元件封裝材料。然而，GNS於大部分高分子基材中無法均勻分散，故相關發展仍受到限制。本研究透過系統性篩查多元醇前驅物(包括乙氧基雙酚A (BAE)，丙氧基雙酚A (BAP)，聚乙二醇(PEG) 和聚丙二醇 (PPG))，作為石墨烯奈米片的分散介質，並研發出一種無溶劑原位合成法，以此獲得具有高濕氣屏障且均勻分散的GNS強化聚氨酯（PU）封裝材料。分散性測試結果顯示，GNS在所有測試條件下，於 BAP以及BAE展現出最佳的分散性，這可歸因於BAP和BAE的苯基結構與GNS的高親和性，使高濃度的GNS能均勻分散在其中。在添加多芳香官能基之異氰酸酯硬化劑（MR-200）後，可於低溫下固化成封裝膜，並同時保持GNS的分散性。於BAE/MR-200 PU的基材中加入0.75 wt%的GNS，測得最低之水氣滲透率(WVTR)為0.418 g/m2 day。使用0.75wt% GNS/BAE/MR-200奈米複合材料作為太陽能電池封裝膠，並將封裝後的元件置於65 ºC/65% RH的濕熱測試條件下，發現相比於商用封裝膠，元件壽命提升82.9%。此外，GNS填料不僅降低了WVTR，還改善了納米複合材料的機械性能並提高了其玻璃轉變溫度（Tg），增加封裝應用的可能性。

Graphene nanosheets (GNS)-reinforced polymers are promising encapsulant materials for electronic devices owing to the impermeability, hydrophobicity and high aspect ratio of GNS, which can help achieve exceptionally low moisture permeability in encapsulants, but their development has been hindered by GNS low tendency to disperse in most polymer matrices. This study develops a solvent-less in-situ polymerization approach to obtain uniformly dispersed GNS-reinforced polyurethane (PU) encapsulants with high moisture-barrier performance through systematic screening of several polyol precursors for PU as dispersion media for GNS, including bisphenol A ethoxylate (BAE), bisphenol A propoxylate (BAP), polyethylene glycol (PEG), and polypropylene glycol (PPG). Dispersibility test results revealed that BAP and BAE exhibited the highest GNS dispersibility among the tested conditions, thanks to their phenyl structure providing high affinity with GNS. Both BAP and BAE allowed high concentrations of GNS to be dispersed within, which upon the addition of an aromatic multifunctional isocyanate hardener (MR-200) could be cured into encapsulant films at low curing temperatures while maintaining the uniform GNS dispersion. With 0.75 wt% of GNS added in the BAE/MR-200 PU matrix, a minimum water vapor transmission rate (WVTR) of 0.418 g/m2 day was obtained, and when applied as encapsulant for a perovskite solar cell device, the device achieved an 82.9% longer lifetime than a commercial encapsulant in a 65ºC/65% R.H. damp heat testing condition. In addition to lowering WVTR, the GNS fillers also improved the mechanical properties and increased the Tg’s of the nanocomposites, broadening their potential encapsulant applications.