Suchergebnisse

Perovskite light-emitting diodes (PeLEDs) have recently shown significant progress with external quantum efficiencies (EQEs) exceeding 20%. However, PeLEDs with pure-red (620-660 nm) light emission, an essential part for full-color displays, remain a great challenge. Herein, a general approach of spacer cation alloying is employed in Ruddlesden-Popper perovskites (RPPs) for efficient red PeLEDs with precisely tunable wavelengths. By simply tuning the alloying ratio of dual spacer cations, the thickness distribution of quantum wells in the RPP films can be precisely modulated without deteriorating their charge-transport ability and energy funneling processes. Consequently, efficient PeLEDs with tunable emissions between pure red (626 nm) and deep red (671 nm) are achieved with peak EQEs up to 11.5%, representing the highest values among RPP-based pure-red PeLEDs. This work opens a new route for color tuning, which will spur future developments of pure-red or even pure-blue PeLEDs with high performance. ; Funding Agencies|ERCEuropean Research Council (ERC)European Commission [717026]; Swedish Research Council VRSwedish Research Council [2018-07109]; Swedish Foundation for International Cooperation in Research and Higher Education [CH2018-7736]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]; Nanyang Technological UniversityNanyang Technological University [M4080514]; Ministry of Education, SingaporeMinistry of Education, Singapore [MOE2019-T2-1-006, MOE-T2EP50120-0004]; National Research Foundation (NRF), SingaporeNational Research Foundation, Singapore [NRF-NRFI2018-04]; NSFCNational Natural Science Foundation of China (NSFC) [61774077]; Key Projects of Joint Fund of Basic and Applied Basic Research Fund of Guangdong Province [2019B1515120073, 2019B090921002, 2020A1414010036]; Guangzhou Key laboratory of Vacuum Coating Technologies and New Energy Materials Open Projects Fund [KFVE20200006]; China Postdoctoral Science FoundationChina Postdoctoral Science Foundation [2020M673055]; Science and Technology Planning Project of Guangzhou, China [201605030008]; Fundamental Research Funds for the Central UniversitiesFundamental Research Funds for the Central Universities [21621008]

Perovskite light-emitting diodes (PeLEDs) have recently shown significant progress with external quantum efficiencies (EQEs) exceeding 20%. However, PeLEDs with pure-red (620-660 nm) light emission, an essential part for full-color displays, remain a great challenge. Herein, a general approach of spacer cation alloying is employed in Ruddlesden-Popper perovskites (RPPs) for efficient red PeLEDs with precisely tunable wavelengths. By simply tuning the alloying ratio of dual spacer cations, the thickness distribution of quantum wells in the RPP films can be precisely modulated without deteriorating their charge-transport ability and energy funneling processes. Consequently, efficient PeLEDs with tunable emissions between pure red (626 nm) and deep red (671 nm) are achieved with peak EQEs up to 11.5%, representing the highest values among RPP-based pure-red PeLEDs. This work opens a new route for color tuning, which will spur future developments of pure-red or even pure-blue PeLEDs with high performance. ; Ministry of Education (MOE) ; National Research Foundation (NRF) ; Published version ; This work was financially supported by the ERC Starting Grant (No. 717026), the Swedish Research Council VR (No. 2018–07109), the Swedish Foundation for International Cooperation in Research and Higher Education (No. CH2018-7736), and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU no. 2009-00971). The computational work for this article was fully performed on resources of the National Supercomputing Centre (NSCC), Singapore (https://www.nscc.sg). S.R., Q.X., X.-K.L., and T.C.S. acknowledge the support from Nanyang Technological University under its start-up grant (M4080514); the Ministry of Education, Singapore, under its AcRF Tier 2 grants (MOE2019-T2-1-006 and MOE-T2EP50120-0004); and the National Research Foundation (NRF), Singapore, under its NRF Investigatorship (NRF-NRFI2018-04). L.H. thanks the NSFC Project (61774077), the Key Projects of Joint Fund of Basic and Applied Basic Research Fund of Guangdong Province (2019B1515120073, 2019B090921002, 2020A1414010036), and the Guangzhou Key laboratory of Vacuum Coating Technologies and New Energy Materials Open Projects Fund (KFVE20200006) for financial support. Z.C. thanks the project funded by China Postdoctoral Science Foundation (2020M673055). J.Q. acknowledges the support by the Science and Technology Planning Project of Guangzhou, China (Grant No. 201605030008), and the Fundamental Research Funds for the Central Universities (Grant No. 21621008)

Ruddlesden-Popper perovskites (RPPs), consisting of alternating organic spacer layers and inorganic layers, have emerged as a promising alternative to 3D perovskites for both photovoltaic and light-emitting applications. The organic spacer layers provide a wide range of new possibilities to tune the properties and even provide new functionalities for RPPs. However, the preparation of state-of-the-art RPPs requires organic ammonium halides as the starting materials, which need to be ex situ synthesized. A novel approach to prepare high-quality RPP films through in situ formation of organic spacer cations from amines is presented. Compared with control devices fabricated from organic ammonium halides, this new approach results in similar (and even better) device performance for both solar cells and light-emitting diodes. High-quality RPP films are fabricated based on different types of amines, demonstrating the universality of the approach. This approach not only represents a new pathway to fabricate efficient devices based on RPPs, but also provides an effective method to screen new organic spacers with further improved performance. ; Funding Agencies|ERC Starting Grant [717026]; National Natural Science Foundation of China [51472164, 61704077]; 1000 Talents Program for Young Scientists of China; Shenzhen Peacock Plan [KQTD2016053112042971]; Educational Commission of Guangdong Province [2015KGJHZ006, 2016KCXTD006]; Science and Technology Planning Project of Guangdong Province [2016B050501005]; Natural Science Foundation of SZU [000050]; Joint NTU-LiU Ph.D. programme on Materials and Nanoscience; European Commission Marie Sklodowska-Curie Actions [691210]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFOMat-LiU) [2009-00971]; JSPS-NTU Joint Research Project [M4082176]; Ministry of Education Tier 2 [MOE 2017-T2-2-002]; Singapore National Research Foundation [NRF-CRP14-2014-03, NRF-NRFI-2018-04]

Despite rapid improvements in efficiency and brightness of perovskite light-emitting diodes (PeLEDs), the poor operational stability remains a critical challenge hindering their practical applications. Here, we demonstrate greatly improved operational stability of high-efficiency PeLEDs, enabled by incorporating dicarboxylic acids into the precursor for perovskite depositions. We reveal that the dicarboxylic acids efficiently eliminate reactive organic ingredients in perovskite emissive layers through an in situ amidation process, which is catalyzed by the alkaline zinc oxide substrate. The formed stable amides prohibit detrimental reactions between the perovskites and the charge injection layer underneath, stabilizing the perovskites and the interfacial contacts and ensuring the excellent operational stability of the resulting PeLEDs. Through rationally optimizing the amidation reaction in the perovskite emissive layers, we achieve efficient PeLEDs with a peak external quantum efficiency of 18.6% and a long half-life time of 682 h at 20 mA cm(-2), presenting an important breakthrough in PeLEDs. ; Funding Agencies|ERC Starting grantEuropean Research Council (ERC) [717026]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; China Scholarship Council (CSC)China Scholarship Council

Room-temperature spin-based electronics is the vision of spintronics. Presently, there are few suitable material systems. Herein, we reveal that solution-processed mixed-phase Ruddlesden-Popper perovskite thin-films transcend the challenges of phonon momentum-scattering that limits spin-transfer in conventional semiconductors. This highly disordered system exhibits a remarkable efficient ultrafast funneling of photoexcited spin-polarized excitons from two-dimensional (2D) to three-dimensional (3D) phases at room temperature. We attribute this efficient exciton relaxation pathway towards the lower energy states to originate from the energy transfer mediated by intermediate states. This process bypasses the omnipresent phonon momentum-scattering in typical semiconductors with stringent band dispersion, which causes the loss of spin information during thermalization. Film engineering using graded 2D/3D perovskites allows unidirectional out-of-plane spin-funneling over a thickness of similar to 600 nm. Our findings reveal an intriguing family of solution-processed perovskites with extraordinary spin-preserving energy transport properties that could reinvigorate the concepts of spin-information transfer. ; Funding Agencies|Nanyang Technological University [M4080514, M4081293]; Ministry of Education [RG104/16, RG173/16, MOE2015-T2-2-015, MOE2016-T2-1-034, MOE2017-T2-1-001]; NTU-A*STAR Silicon Technologies Center of Excellence Program Grant [11235100003]; US Office of Naval Research [ONRGNICOP-N62909-17-1-2155]; Singapore National Research Foundation [NRF-CRP14-2014-03, NRF2018-ITC001-001, NRF-NRFI-2018-04]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [200900971]; European Commission [717026]; Joint NTU-LiU PhD programme on Materials and Nanoscience

Amines are widely employed as additives for improving the performance of metal halide perovskite optoelectronic devices. However, amines are well-known for their high chemical reactivity, the impact of which has yet to receive enough attention from the perovskite light-emitting diode community. Here, by investigating an unusual positive aging effect of CH3NH3I/CsI/PbI2 precursor solutions as an example, we reveal that amines gradually undergo N-formylation in perovskite precursors over time. This reaction is initialized by hydrolysis of dimethylformamide in the acidic chemical environment. Further investigations suggest that the reaction products collectively impact perovskite crystallization and eventually lead to significantly enhanced external quantum efficiency values, increasing from similar to 2% for fresh solutions to greater than or similar to 12% for aged ones. While this case study provides a positive aging effect, a negative aging effect is possible in other perovksite systems. Our findings pave the way for more reliable and reproducible device fabrication and call for further attention to underlying chemical reactions within the perovskite inks once amine additives are included. ; Funding Agencies|ERCEuropean Research Council (ERC)European Commission [717026]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00971]; National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [51472164, 62005126]; 1000 Talents Program for Young Scientists of China; Shenzhen Peacock Plan [KQTD2016053112042971]; Educational Commission of Guangdong Province [2015KGJHZ006]; Research Foundation-Flanders (FWO)FWO [12Y7221N]

Recently, Ruddlesden-Popper perovskites (RPPs) have attracted increasing interests due to their promising stability. However, the efficiency of solar cells based on RPPs is much lower than that based on 3D perovskites, mainly attributed to their poor charge transport. Herein, a simple yet universal method for controlling the quality of RPP films by a synergistic effect of two additives in the precursor solution is presented. RPP films achieved by this method show (a) high quality with uniform morphology, enhanced crystallinity, and reduced density of sub-bandgap states, (b) vertically oriented perovskite frameworks that facilitate efficient charge transport, and (c) type-II band alignment that favors self-driven charge separation. Consequently, a hysteresis-free RPP solar cell with a power conversion efficiency exceeding 12%, which is much higher than that of the control device (1.5%), is achieved. The findings will spur new developments in the fabrication of high-quality, aligned, and graded RPP films essential for realizing efficient and stable perovskite solar cells. ; Funding Agencies|Research Grants Council of the Hong Kong Special Administrative Region, China [11304115]; National Natural Science Foundation of China [51473138]; Joint NTU-LiU Ph.D. programme on Materials and Nanoscience; Swedish Research Council VR [330-2014-6433]; European Commission Marie Sklodowska-Curie action [INCA 600398, 691210]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Nanyang Technological University [M4080514]; Ministry of Education Academic Research Fund Tier 1 grants [RG101/15, RG173/16]; Ministry of Education Academic Research Fund Tier 2 grants [MOE2014-T2-1-044, MOE2015-T2-2-015, MOE2016-T2-1-034]; Singapore National Research Foundation through the Competitive Research Program [NRF-CRP14-2014]; Marie Sklodowska-Curie Fellowship [2016-02051]