Despite their very limited presence in literature, we believe thin-film samples are the most convenient option for highthroughput discovery and development of PS semiconductors for optoelectronics. One of the main reasons is that it is relatively straightforward to engineer compositional and/or temperature gradients along two independent directions of the substrate in a single growth run using physical vapor deposition methods. These gradients typically result in material property variations across the substrate, which can be quickly measured by characterization instruments equipped with automated stages. Thus, it becomes possible to collect property-versus-composition or property-versus-processparameter combinatorial libraries with a high throughput across ternary and quaternary systems alike. This combinatorial approach to materials research for optoelectronic semiconductors has already been applied to both thin-film sulfides and thin-film phosphides. In addition to their compatibility with high-throughput methods, thin films grown from controlled deposition sources are usually compact and have smooth interfaces. These features are ideal for optical and electrical measurements. Finally, standard thin-film thicknesses between tens of nm and a few μm are in the optimal range for most PV/PEC absorbers and LED emitters with reasonable properties. In fact, the large majority of solar cell technologies with meaningful efficiencies is based on thin-film PV absorbers, with silicon being a notable exception due to its unusually low light absorption coefficient. Hence, basic materials research on thin-film samples can immediately be translated into device prototypes.