Surprising “re-entrant” section habits in polymer-based photo voltaic composites may unlock higher effectivity and stability—if scientists replace their modeling approaches.
A brand new research has revealed that natural photo voltaic cells behave way more unpredictably than beforehand thought, exhibiting a “re-entrant” mixing phenomenon that challenges classical polymer science. This perception may open new potentialities for designing extra environment friendly and longer-lasting photo voltaic vitality supplies.
Researchers from North Carolina State College, the Max Planck Institute for Polymer Analysis, and worldwide collaborators created section diagrams of greater than 50 polymer–small molecule acceptor (SMA) composites, the constructing blocks of natural photo voltaic cells. These diagrams, that are crucial for predicting gadget stability and efficiency, confirmed that almost half of the blends defied expectations. As a substitute of blending extra simply at increased temperatures—as most supplies do—they separate when heated and re-mixed when cooled, displaying a counterintuitive “re-entrant” habits.
Not like typical commodity polymers with predictable thermal habits, polymer:SMA composites are ruled by further molecular complexity, making their section transitions extra intricate than conventional fashions can clarify. By specializing in parameters akin to free quantity—the best way molecules develop or contract with warmth—and the glass transition temperature, when supplies freeze right into a non-crystalline strong, the researchers developed a extra full framework to interpret these transitions. Together with these elements in fashions seems to qualitatively reproduce the experimental outcomes.
This deeper understanding of blending habits has important implications. It may information the design of natural photo voltaic cells with increased power-conversion effectivity and larger stability, key to scaling renewable vitality applied sciences. “Polymer:SMA blends supply excessive photo voltaic cell effectivity and stability, however provided that their mixing habits is exactly tuned,” explains Harald Ade, Distinguished Professor at NC State. Jasper Michels of the Max Planck Institute provides that extending fashions to incorporate the glass transition and different parameters is important to seize the complexity of natural semiconductors.
Finally, the work underscores that advancing photo voltaic cell efficiency would require rethinking the physics of natural supplies. Effectivity and stability rely on molecular interactions at a lot smaller scales than we used to account for.
