Editing Light-emitting diode (section)

=== Potential technology ===

A new family of LEDs are based on the semiconductors called [[Perovskite (structure)|perovskites]]. In 2018, less than four years after their discovery, the ability of perovskite LEDs (PLEDs) to produce light from electrons already rivaled those of the best performing [[OLED]]s.<ref>{{Cite journal|last1=Di|first1=Dawei|last2=Romanov|first2=Alexander S.|last3=Yang|first3=Le|last4=Richter|first4=Johannes M.|last5=Rivett|first5=Jasmine P. H.|last6=Jones|first6=Saul|last7=Thomas|first7=Tudor H.|last8=Abdi Jalebi|first8=Mojtaba|last9=Friend|first9=Richard H.|last10=Linnolahti|first10=Mikko|last11=Bochmann|first11=Manfred|date=2017-04-14|title=High-performance light-emitting diodes based on carbene-metal-amides|journal=Science|language=en|volume=356|issue=6334|pages=159–163|doi=10.1126/science.aah4345|pmid=28360136|issn=0036-8075|url=https://ueaeprints.uea.ac.uk/63288/1/Accepted_manuscript.pdf|bibcode=2017Sci...356..159D|arxiv=1606.08868|s2cid=206651900}}</ref> They have a potential for cost-effectiveness as they can be processed from solution, a low-cost and low-tech method, which might allow perovskite-based devices that have large areas to be made with extremely low cost. Their efficiency is superior by eliminating non-radiative losses, in other words, elimination of [[Carrier generation and recombination|recombination]] pathways that do not produce photons; or by solving outcoupling problem (prevalent for thin-film LEDs) or balancing charge carrier injection to increase the [[External quantum efficiency|EQE]] (external quantum efficiency). The most up-to-date PLED devices have broken the performance barrier by shooting the EQE above 20%.<ref name=":3">{{Cite journal|last1=Armin|first1=Ardalan|last2=Meredith|first2=Paul|date=October 2018|title=LED technology breaks performance barrier|journal=Nature|volume=562|issue=7726|pages=197–198|doi=10.1038/d41586-018-06923-y|pmid=30305755|bibcode=2018Natur.562..197M|doi-access=free}}</ref>

In 2018, Cao et al. and Lin et al. independently published two papers on developing perovskite LEDs with EQE greater than 20%, which made these two papers a mile-stone in PLED development. Their device have similar planar structure, i.e. the active layer (perovskite) is sandwiched between two electrodes. To achieve a high EQE, they not only reduced non-radiative recombination, but also utilized their own, subtly different methods to improve the EQE.<ref name=":3" />

In the work of Cao ''et al.'',<ref name="ReferenceA">{{Cite journal|last1=Cao|first1=Yu|last2=Wang|first2=Nana|last3=Tian|first3=He|last4=Guo|first4=Jingshu|last5=Wei|first5=Yingqiang|last6=Chen|first6=Hong|last7=Miao|first7=Yanfeng|last8=Zou|first8=Wei|last9=Pan|first9=Kang|last10=He|first10=Yarong|last11=Cao|first11=Hui|date=October 2018|title=Perovskite light-emitting diodes based on spontaneously formed submicrometre-scale structures|journal=Nature|language=en|volume=562|issue=7726|pages=249–253|doi=10.1038/s41586-018-0576-2|pmid=30305742|issn=1476-4687|bibcode=2018Natur.562..249C|doi-access=free}}</ref> researchers targeted the outcoupling problem, which is that the optical physics of thin-film LEDs causes the majority of light generated by the semiconductor to be trapped in the device.<ref>{{Cite journal|last1=Cho|first1=Sang-Hwan|last2=Song|first2=Young-Woo|last3=Lee|first3=Joon-gu|last4=Kim|first4=Yoon-Chang|last5=Lee|first5=Jong Hyuk|last6=Ha|first6=Jaeheung|last7=Oh|first7=Jong-Suk|last8=Lee|first8=So Young|last9=Lee|first9=Sun Young|last10=Hwang|first10=Kyu Hwan|last11=Zang|first11=Dong-Sik|date=2008-08-18|title=Weak-microcavity organic light-emitting diodes with improved light out-coupling|journal=Optics Express|language=EN|volume=16|issue=17|pages=12632–12639|doi=10.1364/OE.16.012632|pmid=18711500|issn=1094-4087|bibcode=2008OExpr..1612632C|doi-access=free}}</ref> To achieve this goal, they demonstrated that solution-processed perovskites can spontaneously form submicrometre-scale crystal platelets, which can efficiently extract light from the device. These perovskites are formed via the introduction of [[amino acid]] additives into the perovskite [[Precursor (chemistry)|precursor]] solutions. In addition, their method is able to passivate perovskite surface [[Crystallographic defects in diamond|defects]] and reduce nonradiative recombination. Therefore, by improving the light outcoupling and reducing nonradiative losses, Cao and his colleagues successfully achieved PLED with EQE up to 20.7%.<ref name="ReferenceA"/>

Lin and his colleague used a different approach to generate high EQE. Instead of modifying the microstructure of perovskite layer, they chose to adopt a new strategy for managing the compositional distribution in the device—an approach that simultaneously provides high [[luminescence]] and balanced charge injection. In other words, they still used flat emissive layer, but tried to optimize the balance of electrons and holes injected into the perovskite, so as to make the most efficient use of the charge carriers. Moreover, in the perovskite layer, the crystals are perfectly enclosed by MABr additive (where MA is CH<sub>3</sub>NH<sub>3</sub>). The MABr shell passivates the nonradiative defects that would otherwise be present perovskite crystals, resulting in reduction of the nonradiative recombination. Therefore, by balancing charge injection and decreasing nonradiative losses, Lin and his colleagues developed PLED with EQE up to 20.3%.<ref>{{Cite journal|last1=Lin|first1=Kebin|last2=Xing|first2=Jun|last3=Quan|first3=Li Na|last4=de Arquer|first4=F. Pelayo García|last5=Gong|first5=Xiwen|last6=Lu|first6=Jianxun|last7=Xie|first7=Liqiang|last8=Zhao|first8=Weijie|last9=Zhang|first9=Di|last10=Yan|first10=Chuanzhong|last11=Li|first11=Wenqiang|date=October 2018|title=Perovskite light-emitting diodes with external quantum efficiency exceeding 20 per cent|journal=Nature|language=en|volume=562|issue=7726|pages=245–248|doi=10.1038/s41586-018-0575-3|pmid=30305741|issn=1476-4687|bibcode=2018Natur.562..245L|hdl=10356/141016|s2cid=52958604|hdl-access=free}}</ref>