An investigation on the cyclic temperature-dependent performance behaviors of ultrabright air-stable QLEDs.

The aerobic and thermal stability of quantum-dot light-emitting diodes (QLEDs) is an important factor for the practical applications of these devices under harsh environmental conditions. We demonstrate all-solution-processed amber QLEDs with an external quantum efficiency (EQE) of > 14% with almost negligible efficiency roll-off (droop) and a peak brightness of > 600,000 cd/m2, unprecedented for QLEDs fabricated under ambient air conditions. We investigate the device efficiency and brightness level at a temperature range between - 10 and 85 °C in a 5-step cooling/heating cycle. We conducted the experiments at brightness levels higher than 10,000 cd/m2, required for outdoor lighting applications. Our device performance proves thermal stability, with minimal standard deviation in the performance parameters. Interestingly, the device efficiency parameters recover to the initial values upon returning to room temperature. The variations in the performance are correlated with the modification of charge transport characteristics and induced radiative/non-radiative exciton relaxation dynamics at different temperatures. Being complementary to previous studies on the subject, the present work is expected to shed light on the potential feasibility of realizing aerobic-stable ultrabright droop-free QLEDs and encourage further research for solid-state lighting applications.

Metasurface-based bijective illumination collection imaging provides high-resolution tomography in three dimensions.

Microscopic imaging in three dimensions enables numerous biological and clinical applications. However, high-resolution optical imaging preserved in a relatively large depth range is hampered by the rapid spread of tightly confined light due to diffraction. Here, we show that a particular disposition of light illumination and collection paths liberates optical imaging from the restrictions imposed by diffraction. This arrangement, realized by metasurfaces, decouples lateral resolution from depth-of-focus by establishing a one-to-one correspondence (bijection) along a focal line between the incident and collected light. Implementing this approach in optical coherence tomography, we demonstrate tissue imaging at 1.3 µm wavelength with ~ 3.2 µm lateral resolution, maintained nearly intact over 1.25 mm depth-of-focus, with no additional acquisition or computation burden. This method, termed bijective illumination collection imaging, is general and might be adapted across various existing imaging modalities.

Tin Oxide Electron Transport Layers for Air-/Solution-Processed Conventional Organic Solar Cells.

Commercialization of organic solar cells (OSC) is imminent. Interlayers between the photoactive film and the electrodes are critical for high device efficiency and stability. Here, the applicability of SnO2 nanoparticles (SnO2 NPs) as the electron transport layer (ETL) in conventional OSCs is evaluated. A commercial SnO2 NPs solution in butanol is mixed with ethanol (EtOH) as a processing co-solvent to improve film formation for spin and slot-die coating deposition procedures. When processed with 200% v/v EtOH, the SnO2 NPs film presents uniform film quality and low photoactive layer degradation. The optimized SnO2 NPs ink is coated, in air, on top of two polymer:fullerene-based systems and a nonfullerene system, to form an efficient ETL film. In every case, addition of SnO2 NPs film significantly enhances photovoltaic performance, from 3.4 and 3.7% without the ETL to 6.0 and 5.7% when coated on top of PBDB-T:PC61BM and PPDT2FBT:PC61BM, respectively, and from 3.7 to 7.1% when applied on top of the PTQ10:IDIC system. Flexible, all slot-die-coated devices, in air, are also fabricated and tested, demonstrating the versatility of the SnO2 NPs ink for efficient ETL formation on top of organic photoactive layers, processed under ambient condition, ideal for practical large-scale production of OSCs.

Indoor Photovoltaics: Photoactive Material Selection, Greener Ink Formulations, and Slot-Die Coated Active Layers.

Strong visible light absorption is essential to achieve high power conversion efficiency in indoor organic photovoltaics (iOPVs). Here, we report iOPVs that exhibit high efficiency with high voltage under excitation by low power indoor lighting. Inverted type organic photovoltaic devices with active layer blends utilizing the polymer donor PPDT2FBT paired with fullerene, perylene diimide, or ring-fused acceptors that are 6.5-9.1% efficient under 1 sun are demonstrated to reach efficiencies from 10 to 17% under an indoor light source. This performance transcends that of a standard silicon photovoltaic device. Moreover, we compared iOPVs with active layers both spin-cast and slot-die cast from nonhalogenated solvents and demonstrate comparable performance. This work opens a path towards high-efficiency iOPVs for low power electronics.