High-Efficiency Perovskite Solar Cells with Sputtered Metal Contacts.

Sputter deposition produces dense, uniform, adhesive, and scalable metal contacts for perovskite solar cells (PSCs). However, sputter deposition damages the other layers of the PSC. We here report that the damage caused by sputtering metal contacts can be reversed by aerial oxidation. We support this claim by making PSCs sputtered with Au contacts that exhibit higher efficiencies (18.7%) and stabilities than those made with thermally evaporated Au contacts (18.4%). We performed a series of experiments that show that the post-sputtering oxidation step reconstructs the molecular order of the hole transport layer (HTL) and reverses Au atom diffusion into the HTL. This potential restoration was previously neglected in PSC fabrication recipes because metal contact deposition is generally performed after the HTL oxidation. This result is important for scaling PSCs because sputtering is a superior method for manufacturing optimal-quality coatings or large-area devices.

A self-driving laboratory advances the Pareto front for material properties.

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 these conflicting objectives. Here we use a self-driving laboratory, Ada, to define the Pareto front of conductivities and processing temperatures for palladium films formed by combustion synthesis. Ada discovers new synthesis conditions that yield metallic films at lower processing temperatures (below 200 °C) relative to the prior art for this technique (250 °C). This temperature difference makes possible the coating of different commodity plastic materials (e.g., Nafion, polyethersulfone). These combustion synthesis conditions enable us to to spray coat uniform palladium films with moderate conductivity (1.1 × 105 S m-1) at 191 °C. Spray coating at 226 °C yields films with conductivities (2.0 × 106 S m-1) comparable to those of sputtered films (2.0 to 5.8 × 106 S m-1). This work shows how a self-driving laboratoy can discover materials that provide optimal trade-offs between conflicting objectives.