In situ polymerization approach to hybrid 2D black phosphorus/polymer materials: a novel strategy for optoelectronic device fabrication

The synergic effect due to chemical interactions between polymer and nanostructured fillers is the key parameter to provide materials with excellent performance and widespread applications. Improvements in mechanical, thermal, and barrier performance as well as new light-responsiveness or antimicrobial and antifouling features can be obtained by dispersing different 2D nanofillers at the nanoscale level. With reference to the particular class of 2D nanofillers used for optoelectronic devices (graphite and transition metal dichalcogenides), the specific interactions with a polymer matrix can be used to improve the performance of devices and to protect the nanostructures from aging. Black phosphorus (bP) has been extensively investigated for both electronic and photonic applications. However, the difficulty in engineering large scale exfoliation procedures and the intrinsic instability of exfoliated bP towards both moisture and air has so far overshadowed its possible applications. Here, polymer-based hybrid materials containing dispersed black phosphorus nanoflakes (bPn) are prepared, and their structural characteristics analysed and compared, to evaluate the bP dispersion degree and the effectiveness of bPn interfacial interactions with polymer chains aimed at their environmental stabilization. In particular, the polymethyl methacrylate (PMMA) passivation results particularly effective for the hybrid material prepared by polymerization in-situ of MMA, after the direct liquid phase exfoliation in the monomer (without solvent and by operating in ambient conditions). The procedure yields hybrids where the bPn, even if with a gradient of dispersion (size of aggregates), preserve their chemical structure from oxidation and even after UV exposure. The feasibility of this methodology, capable of efficiently exfoliating bP by protecting its structure, is verified using different vinyl monomers: styrene (S) and N-vinylpyrrolidone (NVP) and even by building PS-block-PMMA copolymers. The PMMA-based hybrid is used to design a device without the need of a glove box in any stage of the fabrication, where the nanoflakes show resistance and mobility comparable with electronic-grade liquid phase exfoliated bP. This result proves that the methodology here realized provides hybrid materials as suitable platforms for devices fabrication in the field of optoelectronics. References E. Passaglia et al, Chem. Mat, 30, 2036, (2018) F. Telesio et al., Nanotechnology 29, 295601, (2018) Acknowledgments The authors thank the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement No. 670173) for funding the project PHOSFUN "Phosphorene functionalization: a new platform for advanced multifunctional materials" through an ERC Advanced Grant