GOALI: Additive and Stoichiometry Engineering in Perovskites: Building Deeper Understanding of the Impact on Optoelectronic Properties for Energy Applications

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A key challenge for the semiconductor industry is to develop new materials and devices for cheaper, better performing and more pervasive electronic and energy technologies, including solar cells, light-emitting devices and memory/logic for computation. Over the last ten years, tremendous progress has been demonstrated for the “perovskite” semiconductor family, which offers the promise of both high device performance and potential for ultra-cheap fabrication. As an example, power conversion efficiencies (a key performance metric) for perovskite solar cells has risen from 3 to more than 25 percent over an unprecedented short period of time, and processing for the perovskite component is achieved using simple and cheap solution coating methods. A critical aspect enabling this progress has been the empirical study of how small variations in perovskite composition or additions of foreign components can improve perovskite material formation or device performance. While operational advancements have been made, the mechanism of improvement is not generally understood. This project involves a joint university (Duke) – industry (IBM Corp) collaboration and focuses on using state-of-the-art fabrication and characterization techniques to explore the impact of compositional modifications in perovskite materials and devices. The research targets improved understanding to enable design and demonstration of better performance energy and electronic devices. The project further provides a valuable opportunity for undergraduate, graduate and postdoctoral researchers to experience industrial research through active collaboration with IBM. A partnership with the Duke Shared Materials Instrument Facility also opens a pathway to expose a broad range of younger and non-specialist students to project-related concepts and STEM opportunities. Recent perovskite solar cell literature provides a plethora of new recipes and processing techniques to improve performance. Although solar cell performance is widely used to judge effectiveness of additives/stoichiometry relative to targeted goals, such device structures are complex and may hide intrinsic impacts on perovskite transport/recombination properties (e.g., carrier density, mobility, recombination lifetime and diffusion length). This project targets in depth studies on stoichiometry variations and three classes of additives (polymers, fullerenes and molecular dopants) within perovskite films to more fully understand processes involved in material and device improvement and to push the boundaries of compositional engineering. Through a university (Duke) – industry (IBM Corp) collaboration, the research aims to: 1) Clarify the location of the additives and assess stoichiometry modulation within the perovskite films; 2) determine the impact of additives and stoichiometry variation on carrier density and transport/recombination properties using a newly developed (by GOALI partner IBM) advanced measurement—i.e., carrier-resolved photo-Hall—as well as other characterization approaches (e.g., current-voltage, admittance spectroscopy, photoluminescence, photoemission); and 3) ultimately validate performance and stability improvements through device fabrication/characterization.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.