Advancing the Pareto front for thin-film materials using a self-driving laboratory

Useful materials must satisfy multiple objectives, where the optimization of one objective is often at the expense of another. The Pareto front reports the optimal trade-offs between competing objectives. Here we report a self-driving laboratory, "Ada", that defines the Pareto front of conductivities and processing temperatures for palladium films formed by combustion synthesis. Ada identified previously untested combustion synthesis conditions that resulted in the discovery of lower processing temperatures (below 200 °C) relative to the prior art for this technique (250 °C), a temperature difference that makes the coating of different commodity plastic materials possible (e.g., Nafion, polyethersulfone). These conditions enabled us to use combustion synthesis to spray coat uniform palladium films with moderate conductivity (1.1 $\times$ 10$^5$ S m$^{-1}$) at 191 °C. Spray coating at 226 °C yielded films with conductivities (2.0 $\times$ 10$^6$ S m$^{-1}$) comparable to those of sputtered films (2.0 to 5.8 $\times$ 10$^6$ S m$^{-1}$). This work shows how self-driving laboratories can discover materials satisfying multiple objectives.