Photodetectors exploiting hot electrons have the potential to achieve ultrahigh sensitivity and provide a broadband detection capability. The work by Changlong Liu, Lin Wang, Xiaoshuang Chen and co-workers (article number 1800836) features a novel high-gain photodetection mechanism aimed at the long-wavelength photon band via optical–electrical control of intrinsic hot carriers in graphene. A particular potential gradient can be arbitrarily tailored by just controlling the electric field, improving significantly the device activity beyond traditional bandgap engineering.

Ferroelectric bilayers are leveraged in concert with a metasurface to create tunable infrared devices possessing high-speed, low-power and latchable switching (see article number 1800862 by Thomas E. Beechem and co-workers). Together, these characteristics highlight the potential of ferroelectrics for dynamic infrared elements while also emphasizing the general utility of leveraging phonons to sculpt a material's infrared response.

In article number 1801153, Yan-Qing Li, Jian-Xin Tang and co-workers demonstrate a facile route to achieving indium-free flexible perovskite solar cells with high efficiency and superior repeated bendability. The performance enhancement benefits from the synergetic interplay of a composite electrode stack, consisting of an electrically conductive silver nanowires network, a sol–gel-derived ZnO smoothing layer, and an atomic-layer-deposited TiO₂ passivation layer. This device architecture shows potential for the low-cost roll-to-roll processing of flexible perovskite devices.

The properties and applications of solution-processed polymer and inorganic mesoporous planar 1D photonic crystals are reviewed. Solution processing of these structures offers really low-cost and easy to scale-up fabrication, which attracted a wide technological interest. Properties, growth techniques, and applications of such structures are discussed in the field of emission control, lasing, sensing, and photovoltaics.

Inspired by the biological camouflage systems in the midwater squid Galiteuthis, a new color-change approach using guided reflection is proposed and demonstrated. By directly coupling the background reflection and displaying the reflected light on the surfaces of target, the bioinspired color-change approach achieves both the faithful spectra matching with background and rapid dynamic response in the entire visible region.

A hybrid solar absorber and thermal emitter (HAE) is constructed on one material surface, based on multiple coherence-enhanced absorption. The advantages of a wide angle tolerance and high temperature stability make the HAE a good candidate for specialized solar thermophotovoltaics (STPV) – like cage-type systems with a suppressed radiation loss compared to double-side planar systems, providing potential routes to integrated STPV–TPV for all-climate operation.

A different strategy is proposed here toward off–on type mechanochromic materials by controlling the intersystem crossing (ISC) process through tuning of the solid state packing mode.

A CsPbBr₃-based all-inorganic perovskite light-emitting diode (PeLED) is prepared by controlling of morphology and interface engineering. The optimal device displays an ultrahigh brightness of 179 000 cd m⁻², a peak current efficiency of 28.0 cd A⁻¹, a maximum external quantum efficiency of 7.39%, and an operational lifetime of 6 h.

Carbene-metal-amides based on silver allow organic light-emitting diode (OLED) fabrication by both solution and thermal vapor deposition techniques. Rotational flexibility leads to a thermally activated delayed fluorescence type process with very low activation energy and sub-microsecond triplet harvesting. These are the first OLEDs based solely on silver.

The biological photonic diamond structures inside the scales of weevil Entimus imperialis not only generate colors, but also show an orientation dependent polarization conversion effect. The structural origin of this effect is the symmetry breaking in the unit cell. Bioinspired simplified structures showing the same effect are derived, and one of them (woodpile structure) is fabricated by direct laser writing.

Photodetectors exploiting hot electrons have the potential to achieve ultrahigh sensitivity and broadband detection capabilities. This work features a novel high-gain photodetection aimed at long-wavelength photon band via optical–electrical controlling of intrinsic hot carriers in graphene. A particular potential gradient can be arbitrarily tailored by just controlling the electric field, improving significantly the device activity beyond traditional bandgap engineering.

Tunable infrared devices are demonstrated that leverage domain reconfiguration of ferroelectric bilayers in concert with a plasmonic metasurface. Possessing high-speed (>10 kHz) and low-power (1 µJ mm⁻²) switching along with multiple unpowered states (i.e., latchable), the devices offer a combination of advantages unavailable traditionally. Ferroelectrics thus provide a new path in the pursuit of dynamic infrared elements.

Four thermally activated delayed fluorescence (TADF) emitters with similar constituent segments but different molecular restrictions are developed. The 5′-(10H-spiro[acridine-9,9′-fluoren]-10-yl)-[1,1′:3′,1″-terphenyl]-2′,4,4″-tricarbonitrile (oSpTBC)-based organic light-emitting diodes (OLEDs) exhibit highest efficiencies with a maximum external quantum efficiency (EQE) of 26.8%. These results suggest that appropriately enhancing the molecular restrictions with more rigid constituent segments is an optimal approach to improve the efficiencies of TADF emitters.

White/blue-emitting photoluminescence (PL) of MXene-derived quantum dots (MQDs) is obtained depending on the varied solvents in solvothermal treatment of bulk Ti₃C₂T_x MXene. Fe³⁺ shows specific quenching effect toward the PL of the MQDs in dimethylformamide rather than in others. Moreover, electrochemiluminescence of the MQDs is for the first time observed using persulfate as coreactant.

A blue-excitable yellow phosphor is synthesized via encapsulating Coumarin 6, Rhodamine 6G, and Rhodamine 101 into metal–organic frameworks. The white light-emitting diode fabricated by this phosphor (quantum yield = 82.9%) can emit bright white light with luminous efficiency of 126 lm W⁻¹, ideal color rendering index (88), and low correlated color temperature (4446 K).

Antimony-based resonant tunneling diodes (RTDs) are a promising alternative for mid-infrared (MIR) photodetectors with gain at considerably low operation voltages. Their capability is demonstrated in a tunable diode laser absorption spectroscopy (TDLAS) experiment. The possibility to exploit hole transport by p-type doping provides further advantages and can also be applied to alternative material systems such as GaAs or InP.

The lifetime of white organic light-emitting diodes, comprising a thermally activated delayed fluorescent (TADF) blue emitter and a yellow phosphorescent emitter, is extended using a triplet exciton managing host which selectively quenches the triplet excitons of the blue TADF emitter while harvesting the emission of the yellow phosphorescent emitters.

A novel patterning method is developed for mask-free and flexible fabrication of surface structures through a time-saving spatiotemporal-interference-based femtosecond laser shaping technique. The interference intensity distribution is modulated to arbitrary shapes to process samples. This uniquely simple technique realizes flexible gray-scale patterning on material surfaces, and is applied to THz metasurface fabrication.

Multifunctional emitters endowed with both thermally activated delayed fluorescence and mechanochromic luminescent features are developed by integrating phenoxazine with electron-acceptor [1,2,4]triazolo[1,5-a]pyrimidine. The solution-processed yellow organic light emitting diodes fabricated with these emitters demonstrate a high external quantum efficiency up to 14.3%.

A high-performing solution-processable near-infrared (NIR) to visible light upconversion device, comprising a polymer bulk heterojunction NIR charge generation layer and a CsPbBr₃ light-emitting diode, is demonstrated for visualizing the NIR light. A pixel-less NIR imaging device developed in this work provides a platform for in vivo observation of the NIR light, suitable for applications in bioimaging, disease diagnosis, and wellness monitoring.

Gradient-bandgap perovskite nanoplatelets are fabricated by chemical vapor deposition method. Driven by energy funneling, photogenerated carriers can effectively transfer and emit in the low bandgap region. Accordingly, photoluminescence spectra with different wavelength are observed in nanoplatelets of different thickness. The formation of irreversible and stable phases with illumination is also demonstrated. This investigation greatly benefits future optoelectronic applications.

A facile route to achieve flexible perovskite solar cells with an efficiency of 17.11% is proposed, which benefits from the synergetic interplay among electrically conductive silver nanowires network, sol–gel-derived ZnO protective layer, and ultrathin atomic layer deposition-assisted TiO₂ passivation layer. These flexible devices are repeatedly bendable due to excellent flexural strain resistance.