modulation of its transmittance states. The basic unit of an EC device consists of an electrolyte layer and two symmetric EC electrodes: cathodic and/or anodic EC film deposited on a conductive and transparent substrate. Upon application of an external potential the EC materials can undergo reversible changes of their optical absorption by redox processes and the simultaneous insertion/extraction (coloration/ decoloration) of charge-balancing ions. [10] With regard to the fabrication methods, the most part of the EC devices are typically assembled according to a "sandwichtype" structure, in which a liquid or gel electrolyte is interposed between the two EC electrodes. These systems however suffer from strong limitations, mainly due to defects in homogeneity of coloration, dark spots, and pinholes for the inhomogeneous distribution of the electric field applied, peripheral leakage for inefficient sealing, and, especially, a limited durability and lifetime. [1,11,12] Furthermore their use poses safety problems, requires a more complex sealing procedures and an additional lamination step of the two glass electrodes, limiting the speed of manufacturing process, and increasing costs. Therefore, a huge effort has been devoted to replace liquid and gel electrolytes with solid-state ones and at the same time design new and simplified device architectures. In this context, solid polymer electrolytes (SPEs) have gained great attention due their potential advantages, including electrochemical stability (e.g., wide electrochemical window), low-cost, and ease of processability. [13][14][15] In addition, they have high flexibility, are lightweight, have no leakage, and have good compatibility with electrode materials, making them suitable for scale-up to large area and the realization of multifunctional EC systems with integrative functionalities, such as for example photoelectrochromics or EC electroluminescent devices. [1,2,16] However, suitable ion conduction for EC application is achieved at the expense of their structural and mechanical properties, by adding organic solvents or plasticizing agents that can strongly affect the device stability. Furthermore, SPEs can be degraded by parasitic side reactions with air or moisture, and photo oxidative processes with consequent discoloration of the surface and mechanical damages, thus jeopardizing both the aesthetical and functional characteristics. Recently, two differentThe development of solid-state electrochromics (EC) represents an emerging challenge towards effective integration with other optoelectronic units, such as the EC-organic light-emitting diode devices (EC-OLEDs). By a simultaneous or independent control of optical contrast (EC function) and OLED emission upon electrical activation, these fascinating systems are capable of adaptively modulating solar radiation and display lighting. Here, we report a flexible ECOLED on a single-plastic substrate demonstrating how the rational design of a highly efficient and durable solid-state EC cell enables an increase of overa...