Molecular‐Printed Thermochromic with Fast Color Switching

Abstract Color generation by thermochromic materials offers several advantages over the light‐based technology: a passive circuit element‐driven simplified device layout, cost‐effectiveness, and clear visibility. However, thermochromic materials need to be effectively coupled with an external heat source to induce coloration, which generally involves slow heat transfer processes that are not suitable for potential display applications. Here, a method for molecular printing of a thermochromic ink with a low heat capacity, enabling an unprecedented, fast color switching without any optoelectronic elements, is demonstrated. Molecularly printed ink is patterned on fabricated microheaters that induce transient local heat generation, facilitating local heating and cooling processes. Depending on the density of the thermochromic ink, that is, the number of microcapsuled dyes in the form of a monolayer resulting in a low heat capacity, the chroma of the patterned ink could be increased. Using this technique, the thermochromic ink could be printed over centimeter scales, with cyan‐magenta‐yellow‐black colors at a color‐switching rate of 20–500 ms, to be integrated into the thermochromic device prototype for potential display applications.