TY - JOUR
T1 - Revisiting Sub-Band Gap Emission Mechanism in 2D Halide Perovskites
T2 - The Role of Defect States
AU - Levine, Igal
AU - Menzel, Dorothee
AU - Musiienko, Artem
AU - MacQueen, Rowan
AU - Romano, Natalia
AU - Vasquez-Montoya, Manuel
AU - Unger, Eva
AU - Mora Perez, Carlos
AU - Forde, Aaron
AU - Neukirch, Amanda J.
AU - Korte, Lars
AU - Dittrich, Thomas
N1 - Publisher Copyright:
© 2024 The Authors. Published by American Chemical Society.
PY - 2024/8/21
Y1 - 2024/8/21
N2 - Understanding the sub-band gap luminescence in Ruddlesden-Popper 2D metal halide hybrid perovskites (2D HaPs) is essential for efficient charge injection and collection in optoelectronic devices. Still, its origins are still under debate with respect to the role of self-trapped excitons or radiative recombination via defect states. In this study, we characterized charge separation, recombination, and transport in single crystals, exfoliated layers, and polycrystalline thin films of butylammonium lead iodide (BA2PbI4), one of the most prominent 2D HaPs. We combined complementary defect- and exciton-sensitive methods such as photoluminescence (PL) spectroscopy, modulated and time-resolved surface photovoltage (SPV) spectroscopy, constant final state photoelectron yield spectroscopy (CFSYS), and constant light-induced magneto transport (CLIMAT), to demonstrate striking differences between charge separation induced by dissociation of excitons and by excitation of mobile charge carriers from defect states. Our results suggest that the broad sub-band gap emission in BA2PbI4 and other 2D HaPs is caused by radiative recombination via defect states (shallow as well as midgap states) rather than self-trapped excitons. Density functional theory (DFT) results show that common defects can readily occur and produce an energetic profile that agrees well with the experimental results. The DFT results suggest that the formation of iodine interstitials is the initial process leading to degradation, responsible for the emergence of midgap states, and that defect engineering will play a key role in enhancing the optoelectronic properties of 2D HaPs in the future.
AB - Understanding the sub-band gap luminescence in Ruddlesden-Popper 2D metal halide hybrid perovskites (2D HaPs) is essential for efficient charge injection and collection in optoelectronic devices. Still, its origins are still under debate with respect to the role of self-trapped excitons or radiative recombination via defect states. In this study, we characterized charge separation, recombination, and transport in single crystals, exfoliated layers, and polycrystalline thin films of butylammonium lead iodide (BA2PbI4), one of the most prominent 2D HaPs. We combined complementary defect- and exciton-sensitive methods such as photoluminescence (PL) spectroscopy, modulated and time-resolved surface photovoltage (SPV) spectroscopy, constant final state photoelectron yield spectroscopy (CFSYS), and constant light-induced magneto transport (CLIMAT), to demonstrate striking differences between charge separation induced by dissociation of excitons and by excitation of mobile charge carriers from defect states. Our results suggest that the broad sub-band gap emission in BA2PbI4 and other 2D HaPs is caused by radiative recombination via defect states (shallow as well as midgap states) rather than self-trapped excitons. Density functional theory (DFT) results show that common defects can readily occur and produce an energetic profile that agrees well with the experimental results. The DFT results suggest that the formation of iodine interstitials is the initial process leading to degradation, responsible for the emergence of midgap states, and that defect engineering will play a key role in enhancing the optoelectronic properties of 2D HaPs in the future.
UR - http://www.scopus.com/inward/record.url?scp=85200838497&partnerID=8YFLogxK
U2 - 10.1021/jacs.4c06621
DO - 10.1021/jacs.4c06621
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C2 - 39115182
AN - SCOPUS:85200838497
SN - 0002-7863
VL - 146
SP - 23437
EP - 23448
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 33
ER -