Perovskite active materials stacks have now been studied extensively for their remarkable photophysical properties - materials behaviour that brings them remarkably close to what is possible in voltage, fill factor, and current. The early days of investigation elucidated excellent semiconductor electronic transport (including minority carrier diffusion) characteristics in the active layer; recent studies have shown a particular (and fruitful) focus on the electronic materials interface with charge-extracting/charge-blocking layers. I will review this progress in efficiency, and I will couple the analysis with growing investigations of durability science, and on the materials processing needed to scale.