HOCOM · A Transparent Hole Conductor by Combinatorial Techniques for Next-Generation Energy Conversion Devices

Materials that are both electrically conductive and optically transparent are an essential element in important light conversion applications, such as solar cells, solar fuels, displays, and illumination. Their high conductivity is achieved either through electrons (n-type) or through positively charge holes (p-type). However, the figure of merit of state-of-the-art p-type materials is more than 100 times lower than that of the best n-type materials. Therefore current devices must be designed to have electrons as the main charge carriers at the transparent electrode. If this constraint was removed, new design possibilities could be explored, and even new types of devices (e.g. see-through electronic transistors) could be fabricated. Thus, the goal of this project is to synthesize a p-type transparent conductor with a figure of merit twice as high as that of the current state-of-the-art hole conductive material. I will focus on phosphide materials, as recent theoretical work points to their favorable hole-conducting properties. Among phosphides, I have prioritized one specific material and selected two other promising materials as back-ups. I will learn and apply a high-throughput combinatorial approach championed by my host institution (NREL, USA) in order to accelerate the development of optimal synthesis conditions and dopants. This knowledge will be transferred to my European host (HZB, Germany), which is currently building a full combinatorial research lab. I will use HZB’s combinatorial tools to fabricate simple diode structures on top of the material developed at NREL, using an n-type sulfide semiconductor. Electrical analysis of the diodes will indicate the practical applicability of the new hole conductor in a real device. In parallel, I will be trained in advanced defect spectroscopy techniques at HZB. They will reveal the nature of defects that compensate the dominant p-type character of the hole conductor, thus defining a roadmap for further improvement.