Orange Organic Long-persistent Luminescence from an Electron Donor/Acceptor Binary System

Organic long-persistent luminescence (LPL) materials can overcome the disadvantages of inorganic LPL materials in terms of element sustainability, processability, and color tunability. However, all published electron donor/acceptor binary organic LPL systems show green emission. Here, we report an organic LPL system consisting of N,N,N\u27,N\u27-tetrakis(p-diisobutylaminophenyl)-p-phenylenediamine (TBAPD) as a donor dopant and 2,8-bis(diphenylphosphoryl)dibenzo[b,d]thiophene (PPT) as an acceptor host. The TBAPD/PPT film exhibits orange photoluminescence (CIEx, CIEy = 0.49, 0.49) and LPL (CIEx, CIEy = 0.51, 0.48)

Influence of energy gap between charge-transfer and locally excited states on organic long persistence luminescence

Organic long-persistent luminescence (LPL) is an organic luminescence system that slowly releases stored exciton energy as light. Organic LPL materials have several advantages over inorganic LPL materials in terms of functionality, flexibility, transparency, and solution-processability. However, the molecular selection strategies for the organic LPL system still remain unclear. Here we report that the energy gap between the lowest localized triplet excited state and the lowest singlet charge-transfer excited state in the exciplex system significantly controls the LPL performance. Changes in the LPL duration and spectra properties are systematically investigated for three donor materials having a different energy gap. When the energy level of the lowest localized triplet excited state is much lower than that of the charge-transfer excited state, the system exhibits a short LPL duration and clear two distinct emission features originating from exciplex fluorescence and donor phosphorescence

Many Exciplex Systems Exhibit Organic Long‐Persistent Luminescence

Organic long‐persistent luminescence (OLPL) is a long‐lasting luminescence from a photogenerated intermediated state, such as a charge separated state. Here, it is shown that many exciplex systems exhibit OLPL and that emission pathways of OLPL can be controlled by the relationship among local excited states and charge‐transfer excited states of materials

Organic long persistent luminescence from a thermally activated delayed fluorescence compound

Funding: UK EPSRC (grants EP/ P010482/1, EP/J01771X, EP/J00916, and EP/R035164/1). We gratefully acknowledge funding through the EPSRC NSFCBET lead agency agreement (EP/R010595/1,1706207) and a Leverhulme Trust Research Grant (RPG-2017-231).Organic long‐persistent luminescence (OLPL) is one of the most promising methods for long‐lived‐emission applications. However, present room‐temperature OLPL emitters are mainly based on a bimolecular exciplex system which usually needs an expensive small molecule such as 2,8‐bis(diphenyl‐phosphoryl)dibenzo[b,d]thiophene (PPT) as the acceptor. In this study, a new thermally activated delayed fluorescence (TADF) compound, 3‐(4‐(9H‐carbazol‐9‐yl)phenyl)acenaphtho[1,2‐b]pyrazine‐8,9‐dicarbonitrile (CzPhAP), is designed, which also shows OLPL in many well‐known hosts such as PPT, 2,2′,2″‐(1,3,5‐benzinetriyl)‐tris(1‐phenyl‐1‐H‐benzimidazole) (TPBi), and poly(methyl methacrylate) (PMMA), without any exciplex formation, and its OLPL duration reaches more than 1 h at room temperature. Combining the low cost of PMMA manufacture and flexible designs of TADF molecules, pure organic, large‐scale, color tunable, and low‐cost room‐temperature OLPL applications become possible. Moreover, it is found that the onset of the 77 K afterglow spectra from a TADF‐emitter‐doped film is not necessarily reliable for determining the lowest triplet state energy level. This is because in some TADF‐emitter‐doped films, optical excitation can generate charges (electron and holes) that can later recombine to form singlet excitons during the phosphorescence spectrum measurement. The spectrum taken in the phosphorescence time window at low temperature may consequently consist of both singlet and triplet emission.Publisher PDFPeer reviewe

Synthesis of Zigzag- and Fjord-Edged Nanographene with Dual Amplified Spontaneous Emission

We report the synthesis of a dibenzodinaphthocoronene (DBDNC) derivative as a novel nanographene with armchair, zigzag, and fjord edges, which was characterized by NMR and X-ray crystallography as well as infrared (IR) and Raman spectroscopies. Ultrafast transient absorption (TA) spectroscopy revealed the presence of stimulated emission signals at 655 nm and 710 nm with a relatively long lifetime, which resulted in dual amplified spontaneous emission (ASE) bands under ns-pulsed excitation, indicating the promise of DBNDC as a near-infrared (NIR) fluorophore for photonics. Our results provide new insight into the design of nanographene with intriguing optical properties by incorporating fjord edges.This work was financially supported by the Okinawa Institute of Science and Technology Graduate University (OIST), the Max Planck Society, JSPS KAKENHI Grant No. JP19K24686, and the European Union’s Horizon 2020 Research and Innovation program under grant agreement no. 101017821 (LIGHT-CAP). G. M. P thanks Fondazione Cariplo (Grant no. 2018-0979) for financial support. Researchers from the University of Alicante acknowledge support from the Spanish Ministerio de Ciencia e Innovación and the European Union (Next Generation EU) through grant no. PID2020-119124RB-I00; and to the Conselleria de Innovación, Universidades y Sociedad Digital de la Comunidad Valenciana (Grant No. AICO/2021/093)

Graphene‐Like Conjugated Molecule as Hole‐Selective Contact for Operationally Stable Inverted Perovskite Solar Cells and Modules

Further enhancing the operational lifetime of inverted-structure perovskite solar cells (PSCs) is crucial for their commercialization, and the design of hole-selective contacts at the illumination side plays a key role in operational stability. In this work, the self-anchoring benzo[rst]pentaphene (SA-BPP) is developed as a new type of hole-selective contact toward long-term operationally stable inverted PSCs. The SA-BPP molecule with a graphene-like conjugated structure shows a higher photostability and mobility than that of the frequently-used triphenylamine and carbazole-based hole-selective molecules. Besides, the anchoring groups of SA-BPP promote the formation of a large-scale uniform hole contact on ITO substrate and efficiently passivate the perovskite absorbers. Benefiting from these merits, the champion efficiencies of 22.03% for the small-sized cells and 17.08% for 5 × 5 cm2 solar modules on an aperture area of 22.4 cm2 are achieved based on this SA-BPP contact. Also, the SA-BPP-based device exhibits promising operational stability, with an efficiency retention of 87.4% after 2000 h continuous operation at the maximum power point under simulated 1-sun illumination, which indicates an estimated T80 lifetime of 3175 h. This novel design concept of hole-selective contacts provides a promising strategy for further improving the PSC stability.journal articl

Elimination of light-induced degradation at the nickel oxide-perovskite heterojunction by aprotic sulfonium layers towards long-term operationally stable inverted perovskite solar cells

Nickel oxide (NiOx) is a promising hole-selective contact to produce efficient inverted p-i-n structured perovskite solar cells (PSCs) due to its high carrier mobility and high transparency. However, the light-induced degradation of the NiOx–perovskite heterojunction is the main factor limiting its long-term operational lifetime. In this study, we used the time-resolved mass spectrometry technique to clarify the degradation mechanism of the NiOx-formamidinium–methylammonium iodide perovskite (a common composition for high-performance PSCs) heterojunction under operational conditions, and observed that (1) oxidation of iodide and generation of free protons under 1-sun illumination, (2) formation of volatile hydrogen cyanide, methyliodide, and ammonia at elevated temperatures, and (3) a condensation reaction between the organic components under a high vapor pressure. To eliminate these multi-step photochemical reactions, we constructed an aprotic trimethylsulfonium bromide (TMSBr) buffer layer at the NiOx/perovskite interface, which enables excellent photo-thermal stability, a matched lattice parameter with the perovskite crystal, and robust trap-passivation ability. Inverted PSCs stabilized with the TMSBr buffer layer reached the maximum efficiency of 22.1% and retained 82.8% of the initial value after continuous operation for 2000 hours under AM1.5G light illumination, which translates into a T80 lifetime of 2310 hours that is among the highest operational lifetimes for NiOx-based PSCs

Air-stable Copolymer Exhibiting Near-Infrared Long-Persistent Luminescence

Organic materials exhibiting long-lasting emission in the near infrared are expected to have applications in bio-imaging and other areas. Although room temperature phosphorescence and thermally activated delayed fluorescence display long-lived emission of approximately one minute, organic long-persistent luminescence (OLPL) systems with a similar emission mechanism to inorganic persistent emitters can emit for several hours at room temperature. In particular, OLPL with a hole-diffusion mechanism can function even in the presence of oxygen. However, ionic materials lack long-term stability in neutral organic host owing to aggregation and phase separation. In this study, we synthesised polymers with stable near-infrared persistent luminescence at room temperature via the copolymerisation of electron donors and acceptors. The copolymers exhibit long-persistent luminescence (LPL) at temperatures below the glass transition temperature and can be excited by approximately the entire range of visible light. LPL properties and spectra can be controlled by the dopant