Defect Activity in Lead Halide Perovskites
Silvia Motti a b c, Daniele Meggiolaro d e, Alex Barker b, Carlo Perini b c, James Ball a b, Marina Gandini b c, Roberto Sorrentino b c, Min Kim b, Filippo de Angelis d e, Annamaria Petrozza b
a Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
b CNST, Istituto Italiano di Tecnologia, Milano
c Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci, 32, Milano, Italy
d Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO), CNR-ISTM, Via Elce di Sotto 8, I-06123, Perugia, Italy
e CompuNet, Istituto Italiano di Tecnologia, Genova
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, Silvia Motti, presentation 025
Publication date: 11th February 2019

Perovskite semiconductors have proven to be very promising for photovoltaic application in the last years. Great research effort has been employed towards understanding how the perovskite crystalline and electronic structure relates to their remarkable defect tolerance and surprisingly long carrier lifetimes and high open circuit voltages. At the same time, the material instability often interferes with experimental observations, besides posing a major challenge for commercial application.[1–3] We report a comprehensive investigation of defect activity in lead halide semiconductors combining computational studies with experimental evidences obtained from transient photocurrent, transient absorption and steady-state and time resolved photoluminescence spectroscopy. We have identified the most relevant point defects in MAPbBr3 and MAPbI3 and found that the low trapping and trap-assisted recombination rates associated with electron trapping sites make these a less efficient loss channel when compared to hole trapping defects, therefore the predominance of electron traps can contribute to enhance radiative efficiency and solar cell open circuit voltage.[4,5] We also demonstrate the reactivity of defects and how it relates to the response of the material to external stimuli (i.e. atmosphere, photoexcitation), explaining the photoinstabilities observed in these materials, such as the photoinduced quenching and brightening of photoluminescence and atmosphere induced passivation. This understanding allows us to propose surface engineering methods that effectively block under-coordinated sites, favoring defect healing over defect formation and enhancing the material stability while also improving solar cell open circuit voltage.[6] Our findings on the interplay between defect chemistry and semiconductor performance sheds light to the factors in play regarding the material optimization during the last years of research. Moreover, it also opens the possibility of developing intelligent fabrication methods and further optimizing performance and stability of the material.

Computational studies were performed by D. Meggiolaro. Samples were fabricated by C. A. R. Perini, J. M. Ball, M. Gandini, R. Sorrentino and M. Kim. S. G. Motti acknowledges CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico - Brasil) for the scholarship [206502/2014-1].

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