Dynamic Multicovalent Networks Enabling Stress‐Relieved Sustainable Ultra‐Thin Perovskite Photovoltaics

ABSTRACT Advancing flexible and sustainable energy technologies requires photovoltaic systems that couple high efficiency with mechanical robustness and a minimized environmental footprint. Ultra‐thin perovskite photovoltaics deliver exceptional specific power, yet their deployment is constrained by the lack of sustainable substrates with both mechanical durability under extreme bending. Here, we report a modified bamboo‐derived cellulose vitrimer substrate paired with a permeable interfacial network formed from self‐polymerizing ammonium salts. These dynamic multicovalent networks mitigate strain‐induced interfacial degradation, thereby enabling mechanically robust operation under large strain. Ultra‐thin perovskite photovoltaics fabricated on this platform achieve a champion efficiency of 23.27% and a specific power of 35 W/g, ranking among the highest values reported for ultra‐thin photovoltaics. Notably, the devices maintain 91% of their initial efficiency after 15 000 bending cycles at a 1 mm curvature radius, while the cellulose substrate enables closed‐loop recyclability under mild conditions. This work establishes a scalable and eco‐conscious pathway to high‐performance, mechanically robust perovskite photovoltaics, underscoring how dynamic multicovalent network design can advance sustainable, portable, and wearable energy technologies.