Advanced Optical Materials

Kim, Young‐O; Moon, Byung Joon; Lee, Aram; Kim, Jin Il; Lee, Seoung‐Ki; Lee, Yoon‐Sik; Bae, Sukang; Hong, Byung Hee; Jung, Yong Chae

doi: 10.1002/adom.202170088pmid: N/A

Luo, Xu‐Feng; Li, Fang‐Ling; Zou, Jian‐Wei; Zou, Qian; Su, Jian; Mao, Meng‐Xi; Zheng, You‐Xuan

doi: 10.1002/adom.202100784pmid: N/A

The exploitation of novel fused carbazole/carbonyl emitters is essential to broaden the application of thermally activated delayed fluorescence (TADF) materials for organic light‐emitting diodes (OLEDs). Here, with the aid of the addition and cyclization of the cyano group with the ortho‐carbazole, fused carbazole/carbonyl based TADF emitters are effectively synthesized via this new synthetic strategy. The attachment of ancillary donors including carbazole, diphenylamine, and phenolazine to the fused carbazole/carbonyl skeletons further tunes their emissions from blue to yellow‐green. Particularly, pure‐blue OLEDs incorporating the peripheral carbazole attached emitter exhibit a maximum external quantum efficiency (EQEmax) of 22.3%, with a small full width at half maximum (FWHM) of 48 nm. In addition, the peripheral phenolazine attached yellow‐green emitter shows extremely small singlet−triplet state energy gap (ΔEST) of 0.01 eV, high photoluminescence quantum efficiency of 82.5%, short delayed fluorescence lifetime of 6.2 µs and good OLED performances with an EQEmax of 21.7%, an FWHM of 68 nm and low efficiency roll‐off. These results demonstrate that the new synthetic strategy for fused carbazole/carbonyl molecules provide a valuable reference for the design of high‐efficient TADF emitters.

Balijapalli, Umamahesh; Tang, Xun; Okada, Daichi; Lee, Yi‐Ting; Karunathilaka, Buddhika S. B.; Auffray, Morgan; Tumen‐Ulzii, Ganbaatar; Tsuchiya, Youichi; Sandanayaka, Atula S. D.; Matsushima, Toshinori; Nakanotani, Hajime; Adachi, Chihaya

Wang, Mao; García‐Hemme, Eric; Berencén, Yonder; Hübner, René; Xie, Yufang; Rebohle, Lars; Xu, Chi; Schneider, Harald; Helm, Manfred; Zhou, Shengqiang

doi: 10.1002/adom.202101798pmid: N/A

Zeng, Rui; Yu, Runnan; Jin, Shengli; Jiang, Shan; Zou, Chao; Hu, Siqian; Tan, Zhan'ao

doi: 10.1002/adom.202101246pmid: N/A

Organic tandem solar cells (OTSCs) with the merits of overcoming the S‐Q limit of single‐junction, enhancing and expanding the sunlight harvesting, and minimizing the thermalization energy loss, provide a practical strategy to break through the power conversion efficiency (PCE). However, it is still challenge to realize the multilayered structure by all‐solution processing, especially shortage of interconnection layer (ICL), which physically and electronically connects front and rear subcells to accomplish the complicated tandem structure. Herein, all‐solution‐processed ICL of modified poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (m‐PEDOT) and titanium (diisopropoxide) bis(2,4‐pentanedionate) (TIPD) is invented for constructing inverted OTSCs, and by systematically managing the light and carriers within the stacked multilayers, highly efficient OTSCs are demonstrated. Compared with the traditional ICLs, it avoids the complicated vacuum evaporation and synthesis processes, guaranteeing low cost and high reproducibility. Furthermore, m‐PEDOT/TIPD ICL demonstrates excellent solvent resistance, high transmittance, and good conductivity. To enhance the light harvesting, absorption complementary donors and acceptors are selected as photoactive materials in front and rear subcells, and the transfer matrix formalism optical modeling is introduced to achieve the balanced short‐circuit current density of each subcell in OTSCs. By systematic device optimizations, the best PCE of 15.26% is achieved, among the best results reported for OTSCs.

Das Adhikari, Samrat; Masi, Sofia; Echeverría‐Arrondo, Carlos; Miralles‐Comins, Sara; Sánchez, Rafael S.; Fernandes, Jesum Alves; Chirvony, Vladimir; Martínez‐Pastor, Juan P.; Sans, Victor; Mora‐Seró, Iván

doi: 10.1002/adom.202101024pmid: N/A

An ongoing demand toward lead‐free all‐inorganic cesium metal halide perovskites has presented Sn(II) as an ideal substitute of Pb(II) for applications in optoelectronic devices. The major concern regarding Sn(II) is the instability due to the ambient oxidation to Sn(IV). To expand the scope of traditional perovskite and analogues, herein the synthesis and optical performance of Sn(II)‐doped CsBr, a new material formed by interstitial doping of Sn(II) into the CsBr matrix, are reported for the first time. This material is prepared following an antisolvent mediated recrystallization method using a continuous flow reactor, which is beneficial for scaling up the production compared to traditional batch reactors. Sn(II)‐doped CsBr exhibits broadband orange emission with full‐width‐half‐maximum of 180 nm and a photoluminescence quantum yield of 21.5%. The emission turned to be highly stable over 7 months despite containing Sn(II). It is suggested that this is due to interstitial location of Sn(II) atoms in bulk of microcrystals. A broadband emission and high aerobic stability are attractive properties of the material for white‐light emitting applications.

Li, Yungui; Sachnik, Oskar; Zee, Bas; Thakur, Kalyani; Ramanan, Charusheela; Wetzelaer, Gert‐Jan A. H.; Blom, Paul W. M.

doi: 10.1002/adom.202101149pmid: N/A

In organic light‐emitting diodes (OLEDs), it is typically assumed that a voltage equal to or higher than the energy gap of the emitters is required to observe electroluminescence (EL). However, EL at subgap voltages is observed and proposed to originate from up‐conversion processes, such as fusion of low‐energy triplet excitons. Here, it is demonstrated that EL at subgap voltages in OLEDs is universally present. By using emitters with negligible energy splitting between the singlet and triplet state, the need for incorporating low‐energy triplet excitons is ruled out. The origin of EL at voltages below the energy gap is the recombination of diffused and thermally generated charge carriers, universally present in light‐emitting diodes at nonzero temperatures, theoretically permitting electrical‐to‐optical power‐conversion efficiencies exceeding unity.

Park, Eunseon; Lee, Seungju; Lee, Hyunjung; Lee, Wonmok

doi: 10.1002/adom.202100833pmid: N/A

In this study, core–shell microspheres of poly(methylmethacrylate) (PMMA) and poly(t‐butylmethacrylate) (PtBMA) are synthesized and dispersed in a non‐polar medium exhibiting a structural color in the visible range. The charge stabilization of the PMMA–PtBMA microsphere is achieved because of preferential adsorption of the charged inverse micelles of aerosol‐OT (AOT) on the microsphere surface. While the PtBMA shell enables the dispersion of the microspheres in isoparaffinic fluid, the PMMA core provides an enhanced refractive index contrast with the medium. In comparison to PtBMA‐only microsphere, incorporation of PMMA core not only increases the average refractive index but also increases the surface charge density of the microsphere, which is attributed to strong attraction between the inverse micelles and the microsphere. The optimized crystalline colloidal array (CCA) of the PMMA–PtBMA microsphere shows stronger structural colors than those of the PtBMA‐only spheres because of an enhanced index contrast with the liquid medium, and an improved color tunability is also achieved. A CCA exhibits approximately 50% light transmittance, demonstrating a semi‐transparent display. The repeated voltage biases proved that a CCA has excellent stability. Finally, a low‐angular dependency of the PMMA–PtBMA CCA is confirmed, which is an advantageous feature as an electrophoretic display.

Cunningham, Paul D.; Spillmann, Christopher M.; Melinger, Joseph S.; Ancona, Mario G.; Kim, Young C.; Mathur, Divita; Buckhout‐White, Susan; Goldman, Ellen R.; Medintz, Igor L.

doi: 10.1002/adom.202100884pmid: N/A

DNA scaffolds provide a means to precisely organize chromophores into large biomimetic exciton networks and direct energy transport for nanoscale sensing and light‐harvesting applications. Here, a functional building block of minimal complexity that maximizes the Förster resonance energy transfer (FRET) efficiency is sought. Using a model system consisting of three FRET steps in a 4‐dye cascade: Cy3→Cy3.5→Cy5→Cy5.5, we evaluate how this building block employs multiple interacting versus redundant FRET pathways. Variants of a dual rail design, where one or two copies of each dye are aligned in rigid linear parallel rows, are compared to a split rail format, where varying degrees of spacing are introduced between the rows. The FRET processes are assessed via steady‐state, time‐resolved, and single‐molecule spectroscopy. Experiments and simulation reveal the dual rail design as more efficient than the split rail and suggest the design principle that efficient FRET networks must balance the increase in FRET rate from multiple interacting pathways with undesirable fluorescence quenching between dyes in close proximity. Hybrid fluorophore combinations are identified as a strategy to mitigate this quenching, leading to optimized dual rails capable of 50% end‐to‐end efficiency. These insights can help guide the design of functional photonic wires based on DNA scaffolds.

Xiang, Jin; Li, Shulei; Sun, Zhibo; Chen, Jingdong; Chen, Lei; Pangmai, Mingcheng; Li, Guangcan; Lan, Sheng

doi: 10.1002/adom.202100675pmid: N/A

Gallium (Ga) emerges as a promising material in plasmonics mainly due to its extraordinary properties, such as changeable material phase, tunable plasmon resonances across the ultraviolet to near‐infrared spectral range, and remarkable chemical stability. Here, the efficient white light emission from gallium oxide (Ga2O3) nanoparticles doped with liquid Ga nanodots, which are fabricated by using a laser‐induced oxidation method is reported. The quantum efficiency of Ga/Ga2O3 hybrid nanoparticles is found to be ≈1.3%, which is nearly two orders of magnitude larger than that of liquid Ga nanoparticles. It is revealed that the existence of Schottky barrier and hotspots in Ga/Ga2O3 nanoparticles plays a crucial role in enhancing the quantum efficiency. As an example of practical applications, high‐quality optical data storage is demonstrated by exploiting the controllable formation of Ga/Ga2O3 nanoparticles on a platform of disordered Ga nanoislands. These results suggest the potential applications of Ga/Ga2O3 hybrid nanoparticles in the development of nanoscale light sources and data storage devices.