29.10.18 – EPFL researchers from Michael Grätzel’s lab show how stable, scalable, and efficient perovskite solar cells can be produced through molecular engineering of multifunctional molecular modulators and using solid-state nuclear magnetic resonance to investigate their role in double-cation pure-iodide perovskites. Published in Nature Communications.

Some of the key challenges for hybrid organic-inorganic perovskite solar cells, one of the most promising thin-film photovoltaic technologies, are their limited stability, scalability, and molecular level engineering. Researchers at the Laboratory of Photonics and Interfaces (LPI) and Laboratory of Magnetic Resonance (LMR) at EPFL demonstrate in their Nature Communications article how molecular engineering of multifunctional molecular modulators (MMMs) and using solid-state nuclear magnetic resonance (NMR) to investigate their role in double-cation pure-iodide perovskites can lead to stable, scalable, and efficient perovskite solar cells.

There has been an ongoing effort to overcome some of the limitations associated with perovskite solar cells by using organic additives, however, their microscopic role in the perovskite structure was mostly speculative. The objective of the team lead by Professor Grätzel (LPI), in collaboration with the group of Professor Lyndon Emsley (LMR) was to tackle these challenges through rational molecular design in conjunction with solid-state NMR, as a unique technique for probing interactions within the perovskite material at the atomic level.

The team designed a series of organic molecules equipped with specific functions that act as molecular modulators (MMs), which interact with the perovskite surface through noncovalent interactions, such as hydrogen bonding or metal coordination. While hydrogen bonding can affect the electronic quality of the material, coordination to the metal cation sites could ensure suppression of some of the structural defects, such as undercoordinated metal ions.

Combining the two traits provided the way to simultaneously address the performance and stability, which has led the development of a multifunctional molecular modulator (MMM) with the capacity to interact with the perovskite surface and suppress the defects. As a result, the perovskite solar cells demonstrated performances with remarkable efficiencies exceeding 20% for large areas above 1 cm², which came alongside operational stability even under ambient conditions.

Two researchers currently working at the interface of the teams at EPFL, Dr. Jovana V. Milić (LPI) and Dr. Dominik J. Kubicki (LMR), are excited to apply this approach to more advanced MMMs for stable, scalable, and efficient perovskite solar cells in the future, while hopeful that this stimulates wider application of atomic-level characterization techniques, such as solid-state NMR, for unraveling the mechanisms of their operation.