Defect Passivation in Halide Perovskites
Jinsong Huang a, Charles Van Brackle a
a University of North Carolina – Chapel Hill, 1112 Murray Hall Chapel Hill, NC 27599, North Carolina, United States
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Oral, Charles Van Brackle, presentation 013
Publication date: 11th February 2019

Passivation of electronic defects at the surface and grain boundaries of perovskite materials has become one of the most important strategies to suppress charge recombination in both polycrystalline and single crystalline perovskite solar cells. Although many passivation molecules have been reported, it remains very unclear on the passivation mechanisms of various functional groups. Here, we systematically engineer the structures of passivation molecular functional groups, including carboxyl, amine, isopropyl, phenethyl and tert-butyl-phenethyl groups, and study their passivation capability to perovskites. It reveals the carboxyl and amine groups would heal charged defects via electrostatic interactions, and the neutral iodine related defects can be reduced by the aromatic structures. The judicious control of the interaction between perovskite surface and molecules can further realize the grain boundary passivation, including those are deep toward substrates.  Understanding of the underlining mechanisms allows us to design a new passivation molecule yielding high-performance p-i-n structure solar cells with a stabilized efficiency of 21.4%. The open-circuit voltage (VOC) of a device with perovskite optical bandgap of 1.57 eV reaches 1.23 V, corresponding to a record low VOC deficit of 0.34 V. Our findings provide a guidance for future design of new passivation molecules to realize multiple facets applications in perovskite electronics. The impact of defect passivation on device stability will also be discussed. 

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