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Defects and crystallinity control of perovskite films for light-emitting diodes
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Metal halide perovskites are promising materials for the fabrication of cost-effective and highperformance light-emitting diodes (LEDs), due to their solution processability, high photoluminescence quantum efficiencies (PLQEs) and excellent charge transport properties. Importantly, perovskite LEDs show ultra-pure emission color, which is better than that of the state-of-the-art quantum dot LEDs (QLEDs) and organic LEDs (OLEDs), demonstrating a bright application potential for realizing vivid natural colors display in the future.

In this thesis, we first incorporate natural molecules, e.g. deoxyribonucleic acid (DNA), to passivate FAPbI3 perovskite films. We notice that the existence of carbonyl and amide groups within DNA are important for efficient passivation of perovskite films. Combining the knowledge, we further introduce amino-functionalized molecules into perovskite films and achieve significantly improved efficiency of 21.6 %, which is a record external quantum efficiency (EQE) of perovskite LEDs. We reveal that by weakening the hydrogen bond strength between passivation molecules and organic cations, the interaction between passivation amino groups and defects improves, contributing to more efficient passivation.

We also notice that the underlying substrates play important roles on the film quality of perovskite and the device performance of the ensuing LEDs. Here, we reveal that efficient deprotonation of the undesirable organic cations (Methylammonium (MA+) or Formamidinium (FA+)) by a metal oxide interlayer, e.g. ZnO, with a high isoelectric point, is critical to promote the transition from intermediate phases to highly emissive perovskites. We reveal synergistic effects of precursor stoichiometry and interfacial reactions for high-performance perovskite LEDs, and establish useful guidelines for rational device optimisation. With the knowledge we obtain from the deprotonation process, we further push the EL emission from near-infrared (NIR) (around 800 nm) region to deep red emission (around 700 nm) via cation exchange process between cesium (Cs+) and FA+, which promotes enhanced crystallization of the perovskite films and devices performance simultaneously.

Intensive efforts in the perovskite community have pushed the EQEs of perovskite LEDs to over 20 %for green, red and NIR emission region. However, it is still a long way to go before their practical applications. We believe that efficient control of both the defects and crystallinity of the perovskite films through rational materials development and interfacial modifications is important for the development of perovskite optoelectronic devices. In addition, both our findings on the perovskite film quality control are universal and provide insights to promote the development of perovskites (especially the hybrid ones containing organic components) for the applications of other optoelectronic devices.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2019. , p. 63
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1991
National Category
Materials Chemistry Condensed Matter Physics Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-157713DOI: 10.3384/diss.diva-157713ISBN: 9789176850688 (print)OAI: oai:DiVA.org:liu-157713DiVA, id: diva2:1327492
Public defence
2019-08-27, Planck, Fysikhuset, Campus Valla, Linköping, 09:15 (English)
Opponent
Supervisors
Available from: 2019-06-20 Created: 2019-06-19 Last updated: 2019-07-24Bibliographically approved
List of papers
1. Rational molecular passivation for high-performance perovskite light-emitting diodes
Open this publication in new window or tab >>Rational molecular passivation for high-performance perovskite light-emitting diodes
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2019 (English)In: Nature Photonics, ISSN 1749-4885, E-ISSN 1749-4893, Vol. 13, no 6, p. 418-424Article in journal (Refereed) Published
Abstract [en]

A major efficiency limit for solution-processed perovskite optoelectronic devices, for example light-emitting diodes, is trap-mediated non-radiative losses. Defect passivation using organic molecules has been identified as an attractive approach to tackle this issue. However, implementation of this approach has been hindered by a lack of deep understanding of how the molecular structures influence the effectiveness of passivation. We show that the so far largely ignored hydrogen bonds play a critical role in affecting the passivation. By weakening the hydrogen bonding between the passivating functional moieties and the organic cation featuring in the perovskite, we significantly enhance the interaction with defect sites and minimize non-radiative recombination losses. Consequently, we achieve exceptionally high-performance near-infrared perovskite light-emitting diodes with a record external quantum efficiency of 21.6%. In addition, our passivated perovskite light-emitting diodes maintain a high external quantum efficiency of 20.1% and a wall-plug efficiency of 11.0% at a high current density of 200 mA cm−2, making them more attractive than the most efficient organic and quantum-dot light-emitting diodes at high excitations.

Place, publisher, year, edition, pages
Springer Nature Publishing AG, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-157707 (URN)10.1038/s41566-019-0390-x (DOI)000468752300019 ()
Note

Funding agencies:  ERC Starting Grant [717026]; National Basic Research Program of China (973 Program) [2015CB932200]; National Natural Science Foundation of China [61704077, 51572016, 51721001, 61634001, 61725502, 91733302, U1530401]; Natural Science Foundation of Jiangsu 

Available from: 2019-06-19 Created: 2019-06-19 Last updated: 2019-10-10Bibliographically approved
2. Room-temperature film formation of metal halide perovskites on n-type metal oxides: the catalysis of ZnO on perovskite crystallization
Open this publication in new window or tab >>Room-temperature film formation of metal halide perovskites on n-type metal oxides: the catalysis of ZnO on perovskite crystallization
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2018 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, no 50, p. 6887-6890Article in journal (Refereed) Published
Abstract [en]

We investigate the effect of commonly used solution-processed TiOx, SnO2 and ZnO interlayers on the perovskite film crystallization process. We find that the ZnO/perovskite interface can efficiently catalyze the perovskite crystallization even without thermal annealing.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-149712 (URN)10.1039/c8cc02482k (DOI)000436029000052 ()29781476 (PubMedID)
Note

Funding Agencies|ERC [717026]; Carl Tryggers Stiftelse; European Commission [691210]; China Scholarship Council; VINNMER Marie Curie Fellowships

Available from: 2018-07-24 Created: 2018-07-24 Last updated: 2019-06-19

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