Chemical engineering of lead halide perovskites: from precursor inks to perovskite nanofibers
Sanjay Mathur a, Feray Uenlue a
a Department for Chemistry, Institute of Inorganic Chemistry, University of Cologne, Greinstraße 6, Köln, Germany
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Invited Speaker, Sanjay Mathur, presentation 013
Publication date: 20th April 2022

Hybrid halide perovskites have made significant progress in power conversion efficiencies (up to 25.5%) and high stability achieved through chemical engineering of the AMX3 composition. Compositional engineering of perovskite precursor inks minimizes batch-to-batch variations and fluctuation in PCE values, however the understanding of perovskite inks and solution behavior remains a key step towards the exploitation of solution-processed perovskite devices. Herein, a comprehensive 207Pb nuclear magnetic resonance spectroscopy (NMR) study performed on various lead perovskite precursor inks will be presented. The NMR data provide fresh insights in identifying molecular species that are invariably and predominantly formed in precursor mixtures to coexist with larger networks and colloids. The solution chemistry of PbI2+I- is dominated by the type of connectivity as edge- face- and corner-sharing (PbI6)-octahedra and their dimensionality. The trends in the 207Pb chemical shifts revealed dynamic equilibria in the inks that can be controlled by stoichiometry, nature of the solvents and temperature. Furthermore, perovskite precursor ink development can be applied to fabricate devices beyond the planar device structures, such as direct electrospinning of the three major perovskite solar cell components, namely, photo absorber, hole, and electron transport materials, as continuous single triaxial fibers of μm radial dimensions. These perovskite fibers lay the foundation of materials engineering for fabricating tiny solar cells, which can either be woven into fabrics or incorporated as single fibers to power wearables and a variety of devices or sensors, forming the internet of things.

This research is supported by the Priority Program SPP2196 of the German Science Foundation (DFG; Grant-No. MA 2359/38-1) and F. Ünlü and S. Mathur gratefully acknowledge the financial support. The infrastructural support provided by  the University of Cologne within the Excellence Program QM2 “Quantum Matter and Materials” is thankfully acknowledged.

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