Search

Electron donor and acceptor interactions are the fundamentals for the emergence of optoelectronic functions in most organic devices. In particular, exciplexes, which hold the possibility to utilize dark triplets, are widely investigated in organic light‐emitting diodes. However, the relatively low radiative decay rate with a low photoluminescence quantum yield poses further advanced challenges. Traditionally, it is well recognized that exciplexes are formed through a charge transfer process, i.e., direct electron transfer, by photoexciting either a donor or an acceptor component. In this study, the focus is on a long‐range exciplex system where tris(4‐carbazoyl‐9‐ylphenyl)amine (TCTA) and 2,4,6‐tris[3‐(diphenylphosphinyl)phenyl]−1,3,5‐triazine (PO‐T2T) serve as the donor and acceptor, respectively. Moreover, 1,2‐bis(triphenylsilyl) benzene (UGH2) and bis[2‐(diphenylphosphino)phenyl]ether oxide (DPEPO), having a wide energy gap and a high triplet energy level, are employed as the double insulating layer to suppressing direct electron transfer between the donor and acceptor. The indirect through‐space exciplex formation is demonstrated by the simultaneous excitation of both donor and acceptor layers optically and electrically, providing a new route for exciplex formation. [ABSTRACT FROM AUTHOR]

Recent advances in organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF)‐assisted fluorescence (TAF) attest to the great promise of this technology in practical use. However, the simultaneous realization of high efficiency and device durability in blue OLEDs remains a significant challenge. Clarification of the degradation mechanisms correlated to molecular structure and device configuration is the key to extending the device lifetime. In this study, electron transport materials incorporating two triazine units in close proximity are adopted to use in hole‐blocking and electron‐transporting layers, resulting in superior device performances. In addition, a modified photodegradation experiment reveals that the degradation origins closely relate to charge carriers. The optimization of the device according to the obtained findings leads to 4.5 times extension in the lifetime of the TAF‐OLED using a multiple resonance emitter. These results also provide guidelines for designing robust electron transport materials for blue OLEDs. [ABSTRACT FROM AUTHOR]

Halide perovskites are promising as the light absorbers of solar cells with efficient solar power conversion. However, why the degradation of perovskite solar cells (PSCs), especially at high temperatures, happens has not been completely understood to date. Herein, it is shown that evaporation of 4‐tert‐butylpyridine (4‐tBP) from the hole transport layer (HTL) of 2,2',7,7'‐tetrakis(N,N‐di‐p‐methoxyphenylamino)‐9,9'‐spirobifluorene (spiro‐OMeTAD) is one of possible degradation mechanisms in PSCs at a high temperature of 85 °C. In fresh PSCs, the chemical doping of the spiro‐OMeTAD HTL with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is not so efficient because of the formation of a LiTFSI:4‐tBP complex in the HTL. When PSCs are placed at 85 °C, 4‐tBP gradually evaporates from the HTL, resulting in the dissociation of the LiTFSI:4‐tBP complex. This 4‐tBP evaporation enhances the chemical doping of spiro‐OMeTAD by LiTFSI and makes the hole transport level of the spiro‐OMeTAD HTL deeper, thereby impeding hole extraction at the perovskite/spiro‐OMeTAD/Au interfaces. Herein, the 4‐tBP evaporation by covering PSCs with a fluoro‐polymer CYTOP layer, significantly improving the high‐temperature durability of PSCs, is suppressed. The basic understanding obtained in this study would help promote the spread of more thermally durable PSC products in the future. [ABSTRACT FROM AUTHOR]

Near‐infrared organic light‐emitting diodes (NIR‐OLEDs) possess substantial potential for future valuable applications, such as a light source for sensing applications. However, the low photoluminescence quantum yield (PLQY) of NIR‐emitting molecules represents a significant impediment to these applications. In this study, the impact of the deuteration of both of host (mCP‐d20: 1,3‐Dicarbazole‐benzene‐d20) and guest (BBT‐TPA‐d28: 4,8‐bis[4‐(N,N‐diphenylamino)phenyl]benzo[1,2‐c:4,5‐c']bis[1,2,5]thiadiazole‐d28) on NIR PL properties in the host–guest codeposited film is reported. The 1 wt%‐BBT‐TPA‐d28:mCP‐d20 codeposited film exhibited PLQY of 15 ± 2% with an emission peak wavelength at ≈900 nm, which is about three times higher than that of the film composed of undeuterated molecules. Importantly, the deuteration of only the host or guest does not yield the PLQY up to 15%, underlining the importance of the deuteration of both host and guest molecules in suppressing nonradiative decay processes. The NIR‐OLED with the deuterated codeposited film as an emissive layer demonstrates a maximum external electroluminescence quantum efficiency of 2.3 ± 0.2%. [ABSTRACT FROM AUTHOR]

Although thermally activated delayed fluorescence (TADF) based organic light‐emitting diodes (OLEDs) continue to achieve high efficiencies, their device stability still does not necessarily meet industrial standards. To improve device stability, careful design of a stable host material is crucial. Herein, with reference to a common p‐type host material, 3,3′‐di(9H‐carbazol‐9‐yl)‐1,1′‐biphenyl (mCBP), three novel host materials based on a pyridine unit, mCBP‐1N, CzPyPhCz, and CzPyBF, are systematically designed to improve the stabilities efficiently. The green and blue TADF OLEDs are fabricated with these three new hosts. The maximum external quantum efficiencies (EQEmaxs) of green OLEDs are 20.3 % and 14.0% for CzPyBF and mCBP hosts, respectively. Further, high EQEs of 19.2% and 12.9% are maintained even at 1000 cd m−2. Most importantly, the device lifetime of the CzPyBF host can achieve LT95 of 62.7 h, which is 2.5 times longer than that of mCBP. Also, lower turn‐on voltages are achieved by using CzPyPhCz in blue and green devices. With host engineering, the TADF OLEDs are simultaneously improved with lower turn‐on voltages, higher EQEs, and longer device lifetimes. [ABSTRACT FROM AUTHOR]

Advanced organoboron dyes, incorporating tetra‐boron difluoride (tetra‐BF2) moieties, are developed, demonstrating efficient electrochemiluminescence (ECL) emissions in the green to orange regions through direct ion annihilation. By introducing diverse alkyl modifications in the molecules, luminescence color tuning is achieved via alterations in conjugation and bending angle. A photoluminescence quantum yield of 100% in dilute solutions is successfully achieved. Notably, the introduction of alkyl groups to the methine side stabilizes the radical ionic state, resulting in a high ECL efficiency of 74% through an efficient radical‐ion annihilation pathway. The key factor is that the energy of the annihilation reaction exceeds the S1 energy required for luminescence. Spin density calculations further elucidate the substituent effects on the radical ions of complexes. Moreover, the lasing properties of these materials in the solution‐processed blend films are investigated, revealing a low amplified spontaneous emission (ASE) threshold (Eth) of 6.40 ± 0.24 µJ cm−2, which is notably lower among organic laser materials. This is attributed to their large Stokes shifts and high quantum yield. The excellent ECL and ASE performances establish these materials as a valuable addition to the existing library of organoboron dyes, offering fresh insights into the development of organic solid‐state lasers. [ABSTRACT FROM AUTHOR]