From Design to Device: Challenges and Opportunities in Computational Discovery of p-Type Transparent Conductors

A high-performance p-type transparent conductor (TC) with a wide band gap does not yet exist, but could lead to advances in a wide range of optoelectronic applications and enable new architectures for next-generation photovoltaic (PV) devices. High-throughput computational material screenings have been a promising approach to filter databases and identify new p-type TC candidates, and some of these predictions have been experimentally validated. However, most of these predicted candidates do not have experimentally-achieved properties on par with n-type TCs used in solar cells, and therefore have not yet been used in commercial devices. Thus, there is still a significant divide between transforming predictions into results that are actually achievable in the lab, and an even greater lag in scaling predicted materials into functional devices.<br/><br/>In this work, we introduce a holistic “device-to-design” materials discovery framework through which to identify and contextualize various disconnects in scaling p-type TC predictions into PV devices, and we apply this framework to highlight some of the most pernicious disconnects. One set of disconnects emerges from assumptions and uncertainties in computational assessment and screening. Other disconnects stem from transforming predicted candidates into thin films in the lab: due to challenges including synthesizability, phase purity, dopability, and unwanted absorption, so far no predicted p-type TC grown in the lab performs on par with n-type TCOs. A third key set of disconnect arises from transforming predictions into scalable optoelectronic devices: challenges emerge such as making sufficient contact to the device, tuning band alignments, and growing interfaces free of defects, and other barriers.<br/><br/>We also discuss specific barriers related to scalability and sustainability. Although the ultimate goal of scaling PV is to mitigate climate change, input and outputs from production and deployment may cause unintentional consequences such damage to ecosystems and human health, and there is an ethical responsibility to minimize harm as we scale new materials such as TCs. Historically, life cycle assessments are conducted after technologies reach commercial scale, which can lead to “technology lock-in” that makes it challenging to replace harmful materials. To avoid "locking-in" technologies with detrimental environmental effects, we encourage materials scientists to integrate life cycle thinking throughout the design process, drawing inspiration from recent methodologies like emerging materials risk analysis and anticipatory life cycle assessment.<br/><br/>Lastly, we propose recommendations for materials designers to address these disconnects while designing commercially-relevant wide band gap materials. We offer guidance on how the research community can overcome such disconnects to bring our predictions into fruition in p-TCs and beyond.