Passive radiative cooling forms a sustainable means for cooling of objects through thermal radiation. Along with progress on static cooling systems, there is an emerging need for dynamic control to enable thermoregulation. Here, we demonstrate temperature regu-lation of devices at ambient pressure and temperature by electri-cally tuning their radiative cooling power. Our concept exploits the possibility to electrochemically tune the thermal emissivity and thereby cooling power of a conducting polymer, which enabled reversible control of device temperatures of around 0.25 degrees C at ambient conditions in a sky simulator. Besides tuneable radiative cooling by exposure to the sky, the concept could also contribute to reduced needs for indoor climate control by enabling dynamic control of thermal energy flows between indoor objects, such as be-tween people and walls.

Ultrabroadband electromagnetic (EM) absorbers, especially those covering microwave to terahertz (THz) bands, are urgently desired in multispectral applications such as 6G communication, radar stealth, atmospheric remote sensing, and radio astronomy. Here, we demonstrate that chemically reduced graphene oxide aerogels can be designed as an excellent absorber with the features of ultrabroadband, light weight, compressibility, and high-temperature resistance. This magnetic-free pyramidal absorber shows remarkably broad qualified absorption bandwidth from 4.7 GHz to 4 THz, with reflection loss < -20 dB in the microwave and < -40 dB in the THz band. Especially, an unprecedentedly excellent average absorption intensity of -53.9 dB (absorptivity over 99.999%) is obtained in the frequency range from 0.5 to 4 THz. We experimentally clarify that the gradient macrostructure together with the porous microstructure underlies the continuous impedance matching in such a large frequency range spanning about 3 orders of magnitude and leads to the consecutive strong EM absorption from microwave to terahertz. We believe that this absorber will offer multifunctional and multispectral applications in many scientific and technological fields.

True random number generation is not thought to be possible using a classical approach but by instead exploiting quantum mechanics genuine randomness can be achieved. Here, the authors demonstrate a certified quantum random number generation using a metal-halide perovskite light emitting diode as a source of weak coherent polarisation states randomly producing an output of either 0 or 1. The recent development of perovskite light emitting diodes (PeLEDs) has the potential to revolutionize the fields of optical communication and lighting devices, due to their simplicity of fabrication and outstanding optical properties. Here we demonstrate that PeLEDs can also be used in the field of quantum technologies by implementing a highly-secure quantum random number generator (QRNG). Modern QRNGs that certify their privacy are posed to replace classical random number generators in applications such as encryption and gambling, and therefore need to be cheap, fast and with integration capabilities. Using a compact metal-halide PeLED source, we generate random numbers, which are certified to be secure against an eavesdropper, following the quantum measurement-device-independent scenario. The obtained generation rate of more than 10 Mbit s(-1), which is already comparable to commercial devices, shows that PeLEDs can work as high-quality light sources for quantum information tasks, thus opening up future applications in quantum technologies.

Ruddlesden-Popper perovskites (RPPs) have been demonstrated as a very promising approach for tuning the emission color of perovskite light-emitting diodes (PeLEDs). However, achieving high-performance red PeLEDs with recommendation 2020 color coordinates is still challenging due to the lack of reasonable control over the properties of RPP films. Here, we demonstrate that the judicious selection of spacer cations in RPPs affords a lever for engineering their film properties, including phase distribution, energy funneling process, trap density, and carrier mobility. Four structurally related spacer cations, benzylammonium (BZA), phenylethylammonium (PEA), 3-phenyl-1-propylammonium (PPA), and phenoxyethylammonium (POEA), are studied. Owing to narrow phase distribution, efficient energy funneling, and low trap density, the POEA-based RPP films enable efficient red PeLEDs with a peak external quantum efficiency of 10.3%, a maximum brightness of 1052 cd m- 2, and excellent spectral stability. Significantly, the electroluminescence spectrum represents CIE 1931 color coordinates of (0.71, 0.29), which meets the recommendation 2020 standard (0.708, 0.292). The findings provide useful guidelines for the rational design of new organic spacer cations for RPPs with high performance.

Achieving high-quality cesium-formamidinium lead iodide (CsxFA1_xPbI3) perovskites with tunable band gaps is highly desired for optoelectronic applications including solar cells and light -emit-ting diodes (LEDs). Herein, by utilizing an alkaline-interface-assisted cation-exchange method, we fabricate highly emissive CsxFA1_x PbI3 perovskite films with fine-tunable Cs-FA alloying ratio for emis-sion-tunable near-infrared (NIR) LEDs. We reveal that the deproto-nation of FA+ cations and the formation of hydrogen-bonded gels consisting of CsI and FA facilitated by the zinc oxide underneath effectively removes the Cs-FA ion-exchange barrier, promoting the formation of phase-pure CsxFA1_xPbI3 films with tunable emis-sions filling the gap between that of pure Cs-and FA-based perov-skites. The obtained NIR perovskite LEDs (PeLEDs) peaking from 715 to 780 nm simultaneously demonstrate high peak external quantum efficiencies of over 15%, maximum radiances exceeding 300 W sr_1 m_2, and high power conversion efficiencies above 10% at 100 mA cm_2, representing the best-performing LEDs based on solution-processed NIR emitters in a similar region.

Manganese-based organic-inorganic metal halide composites have been considered as promising candidates for lead-free emitters. However, in spite of their excellent luminescence properties in green and red regions, blue emission-a critical component for white light generation-from pristine manganese-based composites is currently missing. In this work, we successfully achieve blue luminescence center in manganese-based composites through selecting specific organic component methylbenzylamine (MBA). Our approach is fundamentally different from green and red emission in manganese-based composites, which result from manganese-halide frameworks. The coexistence of different luminescence centers in our manganese-based composites is confirmed by photoluminescence (PL) and photoluminescence excitation (PLE) results. As a result of different photoluminescence excitation responses of different emission centers, the resulting emission color can be tuned with selecting different excitation wavelengths. Specifically, a white light emission can be obtained with Commission Internationale de leclairage coordinates of (0.33, 0.35) upon the 330 nm excitation. We further demonstrate the promise of our manganese-based composites in the anti-counterfeiting technology and multicolor lighting. Our results provide a novel strategy for full-spectral emission in manganese-based organic-inorganic metal halide composites and lay a solid foundation for a range of new applications. (C) 2022 Author(s).

Despite rapid improvements in efficiency and brightness of perovskite light-emitting diodes (PeLEDs), the poor operational stability remains a critical challenge hindering their practical applications. Here, we demonstrate greatly improved operational stability of high-efficiency PeLEDs, enabled by incorporating dicarboxylic acids into the precursor for perovskite depositions. We reveal that the dicarboxylic acids efficiently eliminate reactive organic ingredients in perovskite emissive layers through an in situ amidation process, which is catalyzed by the alkaline zinc oxide substrate. The formed stable amides prohibit detrimental reactions between the perovskites and the charge injection layer underneath, stabilizing the perovskites and the interfacial contacts and ensuring the excellent operational stability of the resulting PeLEDs. Through rationally optimizing the amidation reaction in the perovskite emissive layers, we achieve efficient PeLEDs with a peak external quantum efficiency of 18.6% and a long half-life time of 682 h at 20 mA cm(-2), presenting an important breakthrough in PeLEDs.

Despite quick development of perovskite light-emitting diodes (PeLEDs) during the past few years, the fundamental mechanisms on how ion migration affects device efficiency and stability remain unclear. Here, it is demonstrated that the dynamic redistribution of mobile ions in the emissive layer plays a key role in the performance of PeLEDs and can explain a range of abnormal behaviours commonly observed during the device measurement. The dynamic redistribution of mobile ions changes charge-carrier injection and leads to increased recombination current; at the same time, the ion redistribution also changes charge transport and results in decreased shunt resistance current. As a result, the PeLEDs show hysteresis in external quantum efficiencies (EQEs) and radiance, that is, higher EQEs and radiance during the reverse voltage scan than during the forward scan. In addition, the changes on charge injection and transport induced by the ion redistribution also well explain the rise of the EQE/radiance values under constant driving voltages. The argument is further rationalized by adding extra formamidinium iodide (FAI) into optimized PeLEDs based on FAPbI(3), resulting in more significant hysteresis and shorter operational stability of the PeLEDs.

Despite rapid developments of light-emitting diodes (LEDs) based on emerging perovskite nanocrystals (PeNCs), it remains challenging to achieve devices with integrated high efficiencies and high brightness because of the insulating long-chain ligands used for the PeNCs. Herein, we develop highly luminescent and stable formamidinium lead bromide PeNCs capped with rationally designed short aromatic ligands of 2-naphthalenesulfonic acid (NSA) for LEDs. Compared with commonly used oleic acid ligands, the NSA molecules not only preserve the surface properties of the PeNCs during the purification but also notably improve the electrical properties of the assembled emissive layers, ensuring efficient charge injection/transport in the devices. The resulting champion LED with electroluminescence approaching the Rec. 2020 green primary color demonstrates a high brightness of 67 115 cd cm(-2) and a peak external quantum efficiency of 19.2%. More impressively, the device shows negligibly decreased efficiency at an elevated brightness of 20 000 cd cm(-2) and a well-retained efficiency of over 10% at around 65 000 cd cm(-2), presenting a breakthrough in LEDs based on PeNCs.

Metall-halid-perovskiter har visat sig vara en lovande kategori av material för en bred variation av optoelektroniska komponenter med utmärkt prestanda. Jämfört med traditionella oorganiska och organiska halvledare kan perovskit-material enkelt tillverkas och bearbetas med hjälp av lösningsbaserade tekniker vid låga temperaturer samtidigt som de visar hög fotoluminescenseffektivitet, enastående färgrenhet och överlägsna egenskaper gällande laddningstransport. Metall-halidperovskiter uppvisar därmed stora fördelar för att kunna uppnå kostnadseffektiva och högpresterande lysdioder (LED:er).

De första perovskit-baserade lysdioderna (PeLED:er) som kunde drivas under rumstemperaturförhållanden visades upp år 2014. Sedan dess har en rad användbara strategier utvecklats för att optimera de ljusemitterande perovskitmaterialen såväl som diodstrukturerna, vilket lett till märkbart förbättrad prestanda för PeLEDs. Trots snabba framsteg gällandes förbättringen av PeLED:ernas externa kvanteffektivitet, som nu närmar sig kommersiell teknik, är den operativa stabiliteten hos vetenskapens bästa PeLED:er fortfarande dålig, och utgör ett avgörande hinder och en utmaning för att nå praktiska tillämpningar och kommersialisering. En majoritet av de optimeringsstrategier som använts för PeLEDs kommer antingen från strategier som utvecklats för perovskit-solceller eller nuvarande ljusemitterande teknik, t.ex. organiska och kvantprickbaserade lysdioder (OLEDs och QLEDs). Även om dessa strategier är hjälpsamma, så är omfattande undersökningar och djupgående förståelse av faktorer som påverkar egenskaper hos det emitterande perovskitlagret och prestandan av kommande PeLED:er mycket önskvärd för att främja ytterligare framsteg av denna lovande teknik.

I denna avhandling fokuserar vi vår studie på nära infraröda peLED:er baserade på emitterande trijodid-perovskitfilmer tillverkade från prekursorlösningar. Vi undersöker systematiskt de avgörande effekterna som prekursorer, substrat och tillsatser har på filmkvaliteten hos de emitterande perovskitfilmerna. Med den djupgående förståelsen av perovskitkristalliseringsprocessen utvecklade vi en rad användbara gränsyteassisterade strategier för att modulera de emitterande perovskitfilmerna. Detta gör det möjligt för oss att uppnå PeLED:er med integrerade höga EQE:er och utmärkt långsiktig operativ stabilitet som är bättre än dagens bästa PeLED:er.

I den första studien visar vi på den nyckelroll som det alkaliska ZnO-mellanlagret har gällandes påverkan av kristalliseringen av perovskiter, så väl som det stökiometriska förhållandet i prekursorlösningarna. ZnO kan enkelt deprotonera organiska katjoner och eliminera överskottet av FAI, vilket bidrar till en effektiv fasövergång från prekursorkomplex till rena perovskiter med hög emissivitet vilket leder till hög-effektivitets-dioder på 19,6 %. I uppföljningsstudien visade vi att ZnO-deprotonerings-processen av överskott av organiska katjoner också kan initiera; Cs-FA katjonutbyte, förändra legeringsförhållandt mellan Cs och FA, bilda ren-fas-Cs-FA-perovskitfilmer med justerbara emissionstoppar mellan 715 nm och 800 nm samt EQE-värden över 15% för de bästa dioderna.

Trots den förbättrade effektivitet som uppnås genom perovskitkristalliseringsmoduleringen, bildar denna ZnO-deprotoneringsprocess en skadlig effekt på PeLED:ernas stabilitet. En sådan effekt kan påskyndas av Joule-uppvärmning och hög elektrisk fältstyrka under drift. I den tredje studien visade vi ZnOkatalysatorernas viktiga roll när det gäller att införa en effektiv amidiseringsreaktion mellan dikarboxylsyra-tillsatser och överskotts-FAI, vilket förhindrar ovannämnda skadliga gränsytereaktion. Med denna strategi förbättrades peLED:ers operativa halveringstid till nästan 700 timmar vid 20 mA/cm² samtidigt som en hög effektivitet på 18,6% uppehålls.

I det sista arbetet visade vi att kombinationen av två tillsatsämnen (diamin och triakrylat) kan förbättra interaktionerna mellan perovskit och tillsatser avsevärt, tillexempel via tvärbindning av tillsatser och omvandling av överskott av FAI till stabila stora molekyler med hjälp av ZnO-katalysatorer. På detta vis uppnår vi flera funktioner, alltifrån passivering av defekter till perovskitkristallorienteringsreglering. Den rationella förståelsen av gränsyte-interaktioner mellan perovskit, tillsatser och ZnO, gjorde det möjligt för oss att uppnå PeLED:er med en effektivitet på 23,8% samt en enastående driftsstabilitet, med en T₇₀ livslängd på 290 timmar (med en minskning till 70% av den ursprungliga effektiviteten).

Studien som presenteras i denna avhandling visar på en effektiv strategi för att åstadkomma högeffektiva och stabila PeLED:er för framtida kommersialisering. En omfattande förståelse av kemi-struktur-egenskap-prestanda-modulering av perovskiter som assisteras av gränsytor är oumbärlig för utvecklingen av PeLED:er, och vår studie tog ett viktigt steg för den förståelsen.

Multidentate molecular additives are widely used to passivate perovskite, yet the role of chelate effect is still unclear. Here, the authors investigate a wide range of additives with different coordination number and functional moieties to establish correlation between coordination affinity and perovskite crystallisation dynamics. Molecular additives are widely utilized to minimize non-radiative recombination in metal halide perovskite emitters due to their passivation effects from chemical bonds with ionic defects. However, a general and puzzling observation that can hardly be rationalized by passivation alone is that most of the molecular additives enabling high-efficiency perovskite light-emitting diodes (PeLEDs) are chelating (multidentate) molecules, while their respective monodentate counterparts receive limited attention. Here, we reveal the largely ignored yet critical role of the chelate effect on governing crystallization dynamics of perovskite emitters and mitigating trap-mediated non-radiative losses. Specifically, we discover that the chelate effect enhances lead-additive coordination affinity, enabling the formation of thermodynamically stable intermediate phases and inhibiting halide coordination-driven perovskite nucleation. The retarded perovskite nucleation and crystal growth are key to high crystal quality and thus efficient electroluminescence. Our work elucidates the full effects of molecular additives on PeLEDs by uncovering the chelate effect as an important feature within perovskite crystallization. As such, we open new prospects for the rationalized screening of highly effective molecular additives.

Quasi-two-dimensional (Q-2D) perovskites featured with multidimensional quantum wells (QWs) have been the main candidates for optoelectronic applications. However, excessive low-dimensional perovskites are unfavorable to the device efficiency due to the phonon-exciton interaction and the inclusion of insulating large organic cations. Herein, the formation of low-dimensional QWs is suppressed by removing the organic cation 1-naphthylmethylamine iodide (NMAI) through ultrahigh vacuum (UHV) annealing. Perovskite light-emitting diode (PLED) devices based on films annealed with optimized UHV conditions show a higher external quantum efficiency (EQE) of 13.0% and wall-plug efficiency of 11.1% compared to otherwise identical devices with films annealed in a glovebox.

Black phase CsPbI3 is attractive for optoelectronic devices, while usually it has a high formation energy and requires an annealing temperature of above 300 degrees C. The formation energy can be significantly reduced by adding HI in the precursor. However, the resulting films are not suitable for light-emitting applications due to the high trap densities and low photoluminescence quantum efficiencies, and the low temperature formation mechanism is not well understood yet. Here, we demonstrate a general approach for deposition of gamma -CsPbI3 films at 100 degrees C with high photoluminescence quantum efficiencies by adding organic ammonium cations, and the resulting light-emitting diode exhibits an external quantum efficiency of 10.4% with suppressed efficiency roll-off. We reveal that the low-temperature crystallization process is due to the formation of low-dimensional intermediate states, and followed by interionic exchange. This work provides perspectives to tune phase transition pathway at low temperature for CsPbI3 device applications. Exploiting low-temperature formed black phase CsPbI3 for light-emitting applications remains a challenge. Here, the authors propose a method to enable the deposition of gamma -CsPbI3 films at 100C and demonstrate a light-emitting diode with an external quantum efficiency of 10.4% with suppressed efficiency roll-off.

The conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) forms a promising alternative to conventional inorganic conductors, where deposition of thin films via vapour phase polymerization (VPP) has gained particular interest owing to high electrical conductivity within the plane of the film. The conductivity perpendicular to the film is typically much lower, which may be related not only to preferential alignment of PEDOT crystallites but also to vertical stratification across the film. In this study, we reveal non-linear vertical microstructural variations across VPP PEDOT:Tos thin films, as well as significant differences in doping level between the top and bottom surfaces. The results are consistent with a VPP mechanism based on diffusion-limited transport of polymerization precursors. Conducting polymer films with vertical inhomogeneity may find applications in gradient-index optics, functionally graded thermoelectrics, and optoelectronic devices requiring gradient doping.

Ruddlesden-Popper perovskites (RPPs), consisting of alternating organic spacer layers and inorganic layers, have emerged as a promising alternative to 3D perovskites for both photovoltaic and light-emitting applications. The organic spacer layers provide a wide range of new possibilities to tune the properties and even provide new functionalities for RPPs. However, the preparation of state-of-the-art RPPs requires organic ammonium halides as the starting materials, which need to be ex situ synthesized. A novel approach to prepare high-quality RPP films through in situ formation of organic spacer cations from amines is presented. Compared with control devices fabricated from organic ammonium halides, this new approach results in similar (and even better) device performance for both solar cells and light-emitting diodes. High-quality RPP films are fabricated based on different types of amines, demonstrating the universality of the approach. This approach not only represents a new pathway to fabricate efficient devices based on RPPs, but also provides an effective method to screen new organic spacers with further improved performance.

Metal halide perovskites are emerging as promising semiconductors for cost-effective and high-performance light-emitting diodes (LEDs). Previous investigations have focused on the optimisation of the emissive perovskite layer, for example, through quantum confinement to enhance the radiative recombination or through defect passivation to decrease non-radiative recombination. However, an in-depth understanding of how the buried charge transport layers affect the perovskite crystallisation, though of critical importance, is currently missing for perovskite LEDs. Here, we reveal synergistic effect of precursor stoichiometry and interfacial reactions for perovskite LEDs, and establish useful guidelines for rational device optimization. We reveal that efficient deprotonation of the undesirable organic cations by a metal oxide interlayer with a high isoelectric point is critical to promote the transition of intermediate phases to highly emissive perovskite films. Combining our findings with effective defect passivation of the active layer, we achieve high-efficiency perovskite LEDs with a maximum external quantum efficiency of 19.6%.

Rational engineering of the surface properties of perovskite nanocrystals (PeNCs) is critical to obtain light emitters with simultaneous high photoluminescence efficiency and excellent charge transport properties for light-emitting diodes (LEDs). However, the commonly used lead halide sources make it hard to rationally optimize the surface compositions of the PeNCs. In addition, previously developed ligand engineering strategies for conventional inorganic nanocrystals easily deteriorate surface properties of the PeNCs, bringing additional difficulties in optimizing their optoelectronic properties. In this work, a novel strategy of employing a dual-purpose organic lead source for the synthesis of highly luminescent PeNCs with enhanced charge transport property is developed. Lead naphthenate (Pb(NA)(2)), of which the metal ions work as lead sources while the naphthenate can function as the surface ligands afterward, is explored and the obtained products under different synthesis conditions are comprehensively investigated. Monodispersed cesium lead bromide (CsPbBr3) with controllable size and excellent optical properties, showing superior photoluminescence quantum yields up to 80%, is obtained. Based on the simultaneously enhanced electrical properties of the Pb(NA)(2)-derived PeNCs, the resultant LEDs demonstrate a high peak external quantum efficiency of 8.44% and a superior maximum luminance of 31 759 cd cm(-2).