Lignocellulosic-biomass-derived transparent nanopaper is an emerging substrate or functional component for next-generation green optoelectronics. The fabrication of such transparent nanopaper typically needs the delignification of lignocellulose; however, delignification not only is environmentally unfriendly but also impairs the nanopaper properties such as water stability and UV-shielding capacity. In this study, we present a green and facile lignin modification method instead of delignification to fabricate transparent nanopaper from agro-industrial waste with the combined intriguing properties of lignin and cellulose. Because lignin modification selectively removes chromophores without affecting the bulk lignocellulosic structures, the as-prepared lignocellulose nanopaper (LNP) achieved a comparable optical transmittance (∼90%) but superior UV-blocking ability and haze (∼46%) compared with previously reported cellulose (or delignified) nanopaper. The well-preserved lignin structures endowed the transparent LNP with a low surface energy and a small mesoporous size and volume. In addition to a high thermal stability, the transparent LNP exhibited excellent water stability, evidenced by an up to 103° initial water contact angle, a low equilibrium water absorption (<60 wt %), and a high wet mechanical strength (nearly 40% tensile strength and 92% toughness retained in the wet state). Furthermore, we fabricated a GaAs solar cell with the transparent LNP as an advanced light-management layer that leads to significantly improved power conversion efficiency, even under damp conditions. This work sheds light on the conversion of agro-industrial waste to nanopaper with desirable performances for optoelectronics and brings us a step closer toward the scalable production and application of LNP.

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Lignocellulose nanopaper (LNP) assembled from lignocellulose nanofibrils (LCNFs) is an emerging eco-friendly structural material applicable to a variety of fields. Lignin serves as a crucial functional component in the LNP matrix; however, it negatively affects the interfacial hydrogen-bonding behaviors among LCNFs and consequently the inferior mechanical performance of LNP. In this study, a mild ozone-oxidation strategy was used to modify lignin macromolecules in situ without significant degradation of carbohydrate polymers (i.e., cellulose and hemicellulose) in LCNFs whereupon the interfacial hydrogen-bond energy was dramatically improved in the assembly and deformation process of LNP as validated by molecular dynamics simulation. Consequently, the lignin-modified LNP exhibited significantly enhanced tensile strength (from 83 to 140 MPa) and toughness (from 1.9 to 7.1 J/m 3 ), which even surpassed those of conventional cellulose nanopaper. Benefiting from the well-preserved lignocellulosic structure, lignin-modified LNP maintained its inherent favorable water and thermal stability and intriguing optical performance, which supported our developed LNP to be a multifunctional structural material for diversified fields, for example, flexible electronic applications. Additionally, the estimated production cost for our developed LNP was approximately half of that for conventional cellulose nanopaper due to its significantly lower resource inputs such as the material, water, and energy. Overall, our study provides a site-specific macromolecular modulation strategy for the economically and environmentally feasible fabrication of highperformance lignocellulosic nanomaterials toward advanced structural applications.