Fundamental Study of Dopants Effect for Stable Hybrid Perovskite Materials

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Nontechnical Description: Dopants govern and regulate a variety of electronic, optical, thermal and mechanical properties, thus playing a pivotal role in various materials research ranging from metals, semiconductors and insulators. Therefore, fundamental insights to the dopants effect on emerging materials provide a versatile kit to radically tailor the material properties to best fit in their desired practical applications and even lead to discovery of new materials and applications. As a game-changing player in the field of photovoltaics, organic-inorganic hybrid perovskites materials (HPM) has exhibited impressive photovoltaic efficiency. However, HPM still suffer from major challenges including chemical instability and lead toxicity due to: (i) hydration effects, leading to structural failure and (ii) formation of vacancy defects, leading to poor carrier lifetime. In this project, the research team aims to understand the various dopants in HPM and to pursue their synergistic effect towards stable HPM based on fundamental chemical principles. Meanwhile, as an effective way to train the next generation of scientists, the team aims to work with the nearby world-class research facilities at Argonne National Laboratory through existing collaborations with Argonne scientists such that both graduate and undergraduate students with wide diversities can be involved in frontline research projects at their young age, and trained with skills in cutting-edge facilities, interdisciplinary knowledge, critical thinking, problem solving, and team work. Technical Description: The project has a two-fold objective, namely to establish the relationship between dopants (type, amount and location) and the chemical stability of the HPM while minimizing the loss in PV performance; and to provide an atomic level understanding of how the proposed dopants stabilize the vulnerable ions in HPM and affect their PV performance. A synergistic co-doping of both cations and anions is conducted to study their effect on the overall chemical stability. The team is also exploring the interplay between charge-isotropic cationic dopants and multivalent anionic dopants, which are hypothesized to enhance electrostatic coupling between the cationic and anionic parts in HPM, and thus enabling greater rigidity of the overall perovskite structure. The research involves the use of dopants capable of forming strong hydrogen bonding at the atomic level gateway of the perovskite structure to effectively block the ingression of water molecules. Furthermore, the research also involves the use of selected reducing dopants to suppress oxidation of Sn2+ to Sn4+ in Sn-based HPM, based on understanding of what and how reductants can retard the oxidation of Sn2+. Additionally, a high pressure technique is used to minimize the Sn2+ vacancy defects in Sn-based HPM. By prudently designing the type, amount and location of the dopants towards minimal loss in PV efficiency and maximal stability enhancement benefited from the dopants, the ultimate research goal is to provide a clear path to atomically reinforced structure of HPM using dopants as the stabilizing rivets in order to achieve stable and lead-free perovskite solar cells.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.