Perovskite microcells fabricated using swelling-induced crack propagation for colored solar windows

Avian eye-inspired perovskite artificial vision system for foveated and multispectral imaging

Avian eyes have deep central foveae as a result of extensive evolution. Deep foveae efficiently refract incident light, creating a magnified image of the target object and making it easier to track object motion. These features are essential for detecting and tracking remote objects in dynamic environments. Furthermore, avian eyes respond to a wide spectrum of light, including visible and ultraviolet light, allowing them to efficiently distinguish the target object from complex backgrounds. Despite notable advances in artificial vision systems that mimic animal vision, the exceptional object detection and targeting capabilities of avian eyes via foveated and multispectral imaging remain underexplored. Here, we present an artificial vision system that capitalizes on these aspects of avian vision. We introduce an artificial fovea and vertically stacked perovskite photodetector arrays whose designs were optimized by theoretical simulations for the demonstration of foveated and multispectral imaging. The artificial vision system successfully identifies colored and mixed-color objects and detects remote objects through foveated imaging. The potential for use in uncrewed aerial vehicles that need to detect, track, and recognize distant targets in dynamic environments is also discussed. Our avian eye-inspired perovskite artificial vision system marks a notable advance in bioinspired artificial visions.

Structurally colored semitransparent perovskite solar cells using one-step deposition of self-ordering microgel particles

Semitransparent perovskite solar cells (STPSCs) have excellent potential for widespread application as building integrated photovoltaics. Widespread application of STPSCs could result in decreased CO2 footprints for buildings. Unfortunately, STPSCs tend to have poor aesthetic qualities (being usually red-brown in color) and low stability. Building on our previous work, here we use new poly(N-isopropylacrylamide) microgels (PNP MGs) to provide highly ordered non-close packed arrays within perovskite films that reflect some of the incident light to provide structural color to STPSCs. (MGs are swellable crosslinked polymer colloid particles.) We introduce PNP MGs into two different perovskites and achieve a wide gamut of reflected color and iridescence from the perovskite films. Devices containing the MGs have average visible transparency (AVT) values of greater than 25%. The best PCE for a MG-containing STPSC is 10.60% compared to 9.14% for the MG-free control. The MGs not only introduce structural color to the STPSCs but increase the PCE and stability. Equations are provided that enable the reflected color to be predicted from the formulation used to deposit the films. Our work shows that the self-ordering tendency of PNP MGs gives a viable new method for introducing structural color into STPSCs. Because our one-step method for introducing structural color into STPSCs is general, does not introduce any additional processing steps and is scalable whilst also improving device stability, this study may bring deployment of STPSCs closer.

Tunable Structural Coloration in Eccentric Water-in-Oil-in-Water Droplets

Structural colors show diverse advantages such as fade resistance, eco-friendliness, iridescence, and high saturation in comparison with chemical pigments. In this paper, we show tunable structural coloration in colorless water-in-oil-in-water double emulsion droplets via total internal reflection and interference at the microscale concave interfaces. Through experimental work and simulations, we demonstrate that the shell thickness and the eccentricity of the core-shell structures are key to the successful formation of iridescent structural colors. Only eccentric thin-shell water-in-oil-in-water droplets show structural colors. Importantly, structural colors based on water-oil interfaces are readily responsive to a variety of environmental stimuli, such as osmotic pressure, temperature, magnetic fields, and light composition. This work highlights an alternative structural coloration that expands the applications of droplet-based structural colors to aqueous systems.

High-Performance Semi-Transparent Perovskite Solar Cells with over 22% Visible Transparency: Pushing the Limit through MXene Interface Engineering

Semi-transparent perovskite solar cells (ST-PSCs) have attracted enormous attention recently due to their potential in building-integrated photovoltaic. To obtain adequate average visible transmittance (AVT), a thin perovskite is commonly employed in ST-PSCs. While the thinner perovskite layer has higher transparency, its light absorption efficiency is reduced, and the device shows lower power conversion efficiency (PCE). In this work, a combination of high-quality transparent conducting layers and surface engineering using 2D-MXene results in a superior PCE. In situ high-temperature X-ray diffraction provides direct evidence that the MXene interlayer retards the perovskite crystallization process and leads to larger perovskite grains with fewer grain boundaries, which are favorable for carrier transport. The interfacial carrier recombination is decreased due to fewer defects in the perovskite. Consequently, the current density of the devices with MXene increased significantly. Also, optimized indium tin oxide provides appreciable transparency and conductivity as the top electrode. The semi-transparent device with a PCE of 14.78% and AVT of over 26.7% (400-800 nm) was successfully obtained, outperforming most reported ST-PSCs. The unencapsulated device maintained 85.58% of its original efficiency after over 1000 h under ambient conditions. This work provides a new strategy to prepare high-efficiency ST-PSCs with remarkable AVT and extended stability.

Nanomaterial-Based Synaptic Optoelectronic Devices for In-Sensor Preprocessing of Image Data

With the advance in information technologies involving machine vision applications, the demand for energy- and time-efficient acquisition, transfer, and processing of a large amount of image data has rapidly increased. However, current architectures of the machine vision system have inherent limitations in terms of power consumption and data latency owing to the physical isolation of image sensors and processors. Meanwhile, synaptic optoelectronic devices that exhibit photoresponse similar to the behaviors of the human synapse enable in-sensor preprocessing, which makes the front-end part of the image recognition process more efficient. Herein, we review recent progress in the development of synaptic optoelectronic devices using functional nanomaterials and their unique interfacial characteristics. First, we provide an overview of representative functional nanomaterials and device configurations for the synaptic optoelectronic devices. Then, we discuss the underlying physics of each nanomaterial in the synaptic optoelectronic device and explain related device characteristics that allow for the in-sensor preprocessing. We also discuss advantages achieved by the application of the synaptic optoelectronic devices to image preprocessing, such as contrast enhancement and image filtering. Finally, we conclude this review and present a short prospect.

Trilayered Gires-Tournois Resonator with Ultrasensitive Slow-Light Condition for Colorimetric Detection of Bioparticles

Over the past few decades, advances in various nanophotonic structures to enhance light-matter interactions have opened numerous opportunities for biosensing applications. Beyond the successful development of label-free nanophotonic biosensors that utilize plasmon resonances in metals and Mie resonances in dielectrics, simpler structures are required to achieve improved sensor performance and multifunctionality, while enabling cost-effective fabrication. Here, we present a simple and effectual approach to colorimetric biosensing utilizing a trilayered Gires-Tournois (GT) resonator, which provides a sensitive slow-light effect in response to low refractive index (RI) substances and thus enables to distinguish low RI bioparticles from the background with spatially distinct color differences. For low RI sensitivity, by impedance matching based on the transmission line model, trilayer configuration enables the derivation of optimal designs to achieve the unity absorption condition in a low RI medium, which is difficult to obtain with the conventional GT configuration. Compared to conventional bilayered GT resonators, the trilayered GT resonator shows significant sensing performance with linear sensitivity in various situations with low RI substances. For extended applications, several proposed designs of trilayered GT resonators are presented in various material combinations by impedance matching using equivalent transmission line models. Further, comparing the color change of different substrates with low RI NPs using finite-difference time-domain (FDTD) simulations, the proposed GT structure shows surpassing colorimetric detection.

In Situ Super-Hindrance-Triggered Multilayer Cracks for Random Lasing in π-Functional Nanopolymer Films

In situ self-assembly of semiconducting emitters into multilayer cracks is a significant solution-processing method to fabricate organic high- Q lasers. However, it is still difficult to realize from conventional conjugated polymers. Herein, we create the molecular super-hindrance-etching technology, based on the π-functional nanopolymer PG-Cz, to modulate multilayer cracks applied in organic single-component random lasers. Massive interface cracks are formed by promoting interchain disentanglement with the super-steric hindrance effect of π-interrupted main chains, and multilayer morphologies with photonic-crystal-like ordering are also generated simultaneously during the drop-casting method. Meanwhile, the enhancement of quantum yields on micrometer-thick films ( Φ = 40% to 50%) ensures high-efficient and ultrastable deep-blue emission. Furthermore, a deep-blue random lasing is achieved with narrow linewidths ~0.08 nm and high-quality factors Q ≈ 5,500 to 6,200. These findings will offer promising pathways of organic π-nanopolymers for the simplification of solution processes applied in lasing devices and wearable photonics.

Ultrahigh-resolution full-color perovskite nanocrystal patterning for ultrathin skin-attachable displays

High-definition red/green/blue (RGB) pixels and deformable form factors are essential for the next-generation advanced displays. Here, we present ultrahigh-resolution full-color perovskite nanocrystal (PeNC) patterning for ultrathin wearable displays. Double-layer transfer printing of the PeNC and organic charge transport layers is developed, which prevents internal cracking of the PeNC film during the transfer printing process. This results in RGB pixelated PeNC patterns of 2550 pixels per inch (PPI) and monochromic patterns of 33,000 line pairs per inch with 100% transfer yield. The perovskite light-emitting diodes (PeLEDs) with transfer-printed active layers exhibit outstanding electroluminescence characteristics with remarkable external quantum efficiencies (15.3, 14.8, and 2.5% for red, green, and blue, respectively), which are high compared to the printed PeLEDs reported to date. Furthermore, double-layer transfer printing enables the fabrication of ultrathin multicolor PeLEDs that can operate on curvilinear surfaces, including human skin, under various mechanical deformations. These results highlight that PeLEDs are promising for high-definition full-color wearable displays.

Lithography-Free, Large-Area Spatially Segmented Disordered Structure for Light Harvesting in Photovoltaic Modules

Optical losses in photovoltaic (PV) systems cause nonradiative recombination or incomplete absorption of incident light, hindering the attainment of high energy conversion efficiency. The surface of the PV cells is encapsulated to not only protect the cell but also control the transmission properties of the incident light to promote maximum conversion. Despite many advances in elaborately designed photonic structures for light harvesting, the complicated process and sophisticated patterning highly diminish the cost-effectiveness and further limit the mass production on a large scale. Here, we propose a robust/comprehensive strategy based on the hybrid disordered photonic structure, implementing multifaceted light harvesting with an affordable/scalable fabrication method. The spatially segmented structures include (i) nanostructures in the active area for antireflection and (ii) microstructures in the inactive edge area for redirecting the incident light into the active area. A lithography-free hybrid disordered structure fabricated by the thermal dewetting method is a facile approach to create a large-area photonic structure with hyperuniformity over the entire area. Based on the experimentally realized nano-/microstructures, we designed a computational model and performed an analytical calculation to confirm the light behavior and performance enhancement. Particularly, the suggested structure is manufactured by the elastomeric stamps method, which is affordable and profitable for mass production. The produced hybrid structure integrated with the multijunction solar cell presented an improved efficiency from 28.0 to 29.6% by 1.06 times.

A review of tunable photonics: Optically active materials and applications from visible to terahertz

The next frontier of photonics is evolving into reconfigurable platforms with tunable functions to realize the ubiquitous application. The dynamic control of optical properties of photonics is highly desirable for a plethora of applications, including optical communication, dynamic display, self-adaptive photonics, and multi-spectral camouflage. Recently, to meet the dynamic response over broad optical bands, optically active materials have been integrated with the diverse photonic platforms, typically in the dimension of micro/nanometer scales. Here, we review recent advances in tunable photonics with controlling optical properties from visible to terahertz (THz) spectral range. We propose guidelines for designing tunable photonics in conjunction with optically active materials, inherent in wavelength characteristics. In particular, we devote our review to their potential uses for five different applications: structural coloration, metasurface for flat optics, photonic memory, thermal radiation, and terahertz plasmonics. Finally, we conclude with an outlook on the challenges and prospects of tunable photonics.