Low-cost and green fabrication of polymer electronic devices by push-coating the polymer active layers

Due to both their easy processability and compatibility with roll-to-roll processes, polymer electronics is considered to be the most promising technology for the future generation of low-cost electronic devices such as light-emitting diodes and solar cells. However, the state-of-the-art deposition technique for polymer electronics (spin-coating) generates a high volume of chlorinated solution wastes during the active layer fabrication. Here, we demonstrate that devices with similar or higher performances can be manufactured using the push-coating technique in which a polydimethylsiloxane (PDMS) layer is simply laid over a very small amount of solution (less than 1?l/covered cm2) which is then left for drying. Using mm-thick PDMS provides means to control the solvent diffusion kinetics (sorption/retention) and removes the necessity for additional applied pressure to generate the desired active layer thickness. Unlike spin-coating, push-coating is a slow drying process which induces a higher degree of crystallinity in the polymer thin film without the necessity for a post-annealing step. The polymer light-emitting diodes and solar cells prepared by push-coating exhibit slightly higher performances with respect to the reference spin-coated devices while at the same time reducing the amounts of active layer materials and chlorinated solvents by 50 times and over 20 times, respectively. These increased performances can be correlated to the higher polymer crystallinities obtained without applying a post-annealing treatment. As push-coating is a roll-to-roll compatible method, the results presented here open the path to low-cost and eco-friendly fabrication of a wide range of emerging devices based on conjugated polymer materials.