Simultaneously achieving efficient and robust blue organic light-emitting diodes (OLEDs) is a grand challenge, where one of the limitations lies in hole transport materials (HTMs). Here, we unravel the degradation mechanisms of the most promising and widely used HTM, di-[4-(N,N-di-p-tolyl-amino)-phenyl]cyclohexane (TAPC). A luminescent defect is discovered in TAPC during degradation in blue OLEDs, which is induced by a two-step electron-induced process. To suppress this degradation, we propose a negative-charge management strategy by introducing a strong electron-withdrawing material, fullerene, at the TAPC interface. This strategy is proven effective in blue phosphorescent OLEDs, resulting in not only a 10-fold enhancement in operational lifetime but also a significant suppression in efficiency roll-off at high brightness over 30 000 cd m-2. Our findings offer a feasible solution to improve the operational stability of blue OLEDs in which the degradation of HTM plays a role, potentially accelerating the commercialization of high-efficiency long-lasting OLED displays.

Luminescent solar concentrators (LSCs) based on high photoluminescence quantum yield (PLQY) quasi-2D perovskites demonstrate superior edge light collection capability, which breaks the etendue limit and achieves signal reception in visible light communication (VLC). Herein, 2,7-bis(diphenylphosphoryl)-9,9-spirobifluorene (SPPO13) is introduced into the Q-2D RP-phase perovskite (BA(2)Cs(4)Pb(5)Br(16), <n> = 5), realizing dual effects of defect passivation and small n value phase suppression. The emission peak of the optimized film is at 518 nm with a maximum PLQY of 99.49%, and it shows excellent air storage and UV stability. The Q-2D perovskite LSCs realize an external optical efficiency of 4.3% under a geometric factor G of 3.75 and are applied to VLC systems for the first time. As a result, the VLC systems achieve an FoV exceeding +/- 30 degrees and a bandwidth of 165 MHz (-20 dB), enabling a light communication rate of 432 Mbps. This work expands the interdisciplinary application of Q-2D perovskite LSCs in VLC systems, liberating VLC receivers from complex active pointing and tracking systems.

The bottom small n phases in quasi-two-dimensional (Q-2D) perovskite films significantly hinder their photovoltaic performance development due to their severely low conductivity and nonideal band alignment in the corresponding solar cells. In this study, we successfully suppressed the growth of small n phases in Q-2D Ruddlesden-Popper (RP) perovskite (BA2MA4Pb5I16, < n > = 5) films by introducing 2,7-bis(diphenylphosphoryl)-9,9 '-spirobifluorene (SPPO13) as an additive into the perovskite precursor solution. It is interesting to find that the hole transport layer poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) in our p-i-n device can attract the SPPO13 due to the pi-pi stacking effect. As a result, the SPPO13 concentrates at the bottom, and the coordination between SPPO13 and PbI2 leads to more [PbI6]4- octahedra gathering at the downside of the Q-2D perovskite film. Thereby, more large n phases remain at the bottom, and the unwanted small n phases are suppressed. The optimized device achieves a remarkable power conversion efficiency of 18.41%, which, according to our knowledge, is the highest value for the BA-MA-based perovskite. Moreover, our device also demonstrates outstanding stability, maintaining 99.5% and 95.3% of the initial efficiency after being stored for over 3500 h and under maximum power point tracking operation for over 400 h, respectively. Unlike conventional methods that primarily address bulk or interface properties, this approach uniquely combines pi-pi stacking effects and defect passivation through phosphine oxide groups, leading to enhanced crystallinity, vertical orientation, and suppressed nonradiative recombination. This work provides a new approach to regulate n-phase growth and promote the photovoltaic behavior of Q-2D perovskite solar cells.

Sustained amplified stimulated emission (ASE) under continuous-wave (cw) excitation is a prerequisite for any new gain material being developed for lasing applications. Despite the great success achieved in colloidal quantum dot (QD) lasers, the cw light amplification is hampered by the high pump threshold and thermal effects of QD solids. Herein, the first-ever cw ASE and lasing from QDs relevant for practical implementations are realized by adopting the microfluidic dot-in-matrix design. Leveraging on the transient and steady-state gain spectroscopy, it is demonstrated that the high-concentration dispersed QDs with a gain feature customized for cw pumping render the low pump threshold (approximate to 340 W cm-2). Meanwhile, the QD micro-liquids effectively dissipate the heat arising from the nonradiative multi-carrier recombination. As such, the unprecedented two-band cw ASE and long-lasting cw lasing with coherent output beam are realized. The findings open the door to practical QD lasers and may unlock new possibilities in optofluidics and optoelectronics.

The formation of bubbles and fractures on the top electrode surface is one of the key factors that leads to the degradation of organic devices. This degradation can be directly observed through optical microscopy but only in low spatial resolution of several micrometers due to limited optical contrast between the bubbles and their surroundings. Here, we present a nonintrusive capacitance method to characterize electrode damage with improved accuracy and testing efficiency. For serious degradation with a large damage area at the top electrode (almost more than 10 mu m), the relative drop in capacitance after degradation is consistent with the results derived by optical microscopy. For initial degradation with a damage area below the resolution of optical microscopy (even less than 1 mu m), our proposed capacitance method still works well, which is validated by atomic force microscopy results.

The threshold carrier density, conventionally evaluated from optical pumping, is a key reference parameter towards electrically pumped lasers with the widely acknowledged assumption that optically excited charge carriers relax to the band edge through an ultrafast process. However, the characteristically slow carrier cooling in perovskites challenges this assumption. Here, we investigate the optical pumping of state-of-the-art bromide- and iodine-based perovskites. We find that the threshold decreases by one order of magnitude with decreasing excitation energy from 3.10 eV to 2.48 eV for methylammonium lead bromide perovskite (MAPbBr(3)), indicating that the low-energy photon excitation facilitates faster cooling and hence enables efficient carrier accumulation for population inversion. Our results are then interpreted due to the coupling of phonon scattering in connection with the band structure of perovskites. This effect is further verified in the two-photon pumping process, where the carriers relax to the band edge with a smaller difference in phonon momentum that speeds up the carrier cooling process. Furthermore, by extrapolating the optical pumping threshold to the band edge excitation as an analog of the electrical carrier injection to the perovskite, we obtain a critical threshold carrier density of similar to 1.9 x 10(17) cm(-3), which is one order of magnitude lower than that estimated from the conventional approach. Our work thus highlights the feasibility of metal halide perovskites for electrically pumped lasers.

The development of perovskite light-emitting diodes (PeLEDs) with both high efficiency and excellent stability remains challenging. Herein, a strong correlation between the lattice strain in perovskite films and the stability of resulting PeLEDs is revealed. Based on high-efficiency PeLEDs, the device lifetime is optimized by rationally tailoring the lattice strain in perovskite films. A PeLED with a high peak external quantum efficiency of 18.2% and a long lifetime of 151 h (T-70, under a current density of 20 mA cm(-2)) is realized with a minimized lattice strain in the perovskite film. In addition, an increase in the lattice strain is found during the long-time device stability test, indicating that the degradation of the local perovskite lattice structure could be one of the degradation mechanisms for long-term stable PeLEDs.

Incorporating chiral organic compounds into metal halide frames is a common and useful method to introduce chirality in metal halide composites. The structures of resulting racemic and chiral composites are usually considered to be nearly identical owing to similar chemical bonding. In this work, by incorporating chiral MBABr (bromide methylbenzylamine) into an inorganic frame, a significant crystallization difference between the resulting racemic and chiral metal halide composites is observed, as confirmed by both structural and spectroscopic measurements. In addition, the structural transformation in the chiral composites can also be induced by moisture, ascribed to the asymmetric hydrogen bonding in chiral materials. These results provide new insights for the future synthesis of chiral materials and open up new possibilities to advance the materials functionalities.