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Inverted planar perovskite solar cells offer opportunities for a simplified device structure compared with conventional mesoporous titanium oxide interlayers. However, their lower open-circuit voltages result in lower power conversion efficiencies. Using mixed-cation lead mixed-halide perovskite and a solution-processed secondary growth method, Luo et al. created a surface region in the perovskite film that inhibited nonradiative charge-carrier recombination. This kind of solar cell had comparable performance to that of conventional cells. Science , this issue p. 1442 High open-circuit voltages were achieved for planar perovskite solar cells by creating a graded junction. The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages ( V oc ). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in V oc by up to 100 millivolts. We achieved a high V oc of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.

Multiple ultrashort laser pulses are widely used in optical spectroscopy, optoelectronic manipulation, optical imaging and optical signal processing etc. The laser pulse multiplication, so far, is solely realized by using the optical setups or devices to modify the output laser pulse from the optical gain medium. The employment of these external techniques is because the gain medium itself is incapable of modifying or multiplying the generated laser pulse. Herein, with single femtosecond laser pulse excitation, we achieve the double-pulsed stimulated emission with pulse duration of around 40 ps and pulse interval of around 70 ps from metal-halide perovskite multiple quantum wells. These unique stimulated emissions originate from one fast vertical and the other slow lateral high-efficiency carrier funneling from low-dimensional to high-dimensional quantum wells. Furthermore, such gain medium surprisingly possesses nearly Auger-free stimulated emission. These insights enable us a fresh approach to multiple the ultrashort laser pulse by gain medium. Laser pulse multiplication is desired in many applications but has been challenging to realize by gain medium. Here Guo et al. achieve double-pulsed stimulated emission in quasi-2D metal-halide perovskites due to the two-channel carrier funneling effect in their multiple-quantum-wells structure.

Controlling the high-power laser transmittance is built on the diverse manipulation of multiple nonlinear absorption (NLA) processes in the nonlinear optical (NLO) materials. According to standard saturable absorption (SA) and reverse saturable absorption (RSA) model adapted for traditional semiconductor materials, the coexistence of SA and RSA will result in SA induced transparency at low laser intensity, yet switch to RSA with pump fluence increasing. Here, we observed, in contrast, an unusual RSA to SA conversion in quasi-two-dimensional (2D) perovskite film with a low threshold around 2.6 GW cm −2 . With ultrafast transient absorption (TA) spectra measurement, such abnormal NLA is attributed to the competition between excitonic absorption enhancement and non-thermalized carrier induced bleaching. TA singularity from non-thermalized “Fermi Sea” is observed in quasi-2D perovskite film, indicating an ultrafast carrier thermalization within 100 fs. Moreover, the comparative study between the 2D and 3D perovskites uncovers the crucial role of hot-carrier effect to tune the NLA response. The ultrafast carrier cooling of quasi-2D perovskite is pointed out as an important factor to realize such abnormal NLA conversion process. These results provide fresh insights into the NLA mechanisms in low-dimensional perovskites, which may pave a promising way to diversify the NLO material applications. Controlling the high-power laser transmittance is built on the diverse manipulation of multiple nonlinear absorption processes in the nonlinear optical materials. Here, the authors demonstrate the crucial role of hot-carrier effect to tune the nonlinear absorption response in quasi-2D perovskite films.

Intragrain impurities can impart detrimental effects on the efficiency and stability of perovskite solar cells, but they are indiscernible to conventional characterizations and thus remain unexplored. Using in situ scanning transmission electron microscopy, we reveal that intragrain impurity nano-clusters inherited from either the solution synthesis or post-synthesis storage can revert to perovskites upon irradiation stimuli, leading to the counterintuitive amendment of crystalline grains. In conjunction with computational modelling, we atomically resolve crystallographic transformation modes for the annihilation of intragrain impurity nano-clusters and probe their impacts on optoelectronic properties. Such critical fundamental findings are translated for the device advancement. Adopting a scanning laser stimulus proven to heal intragrain impurity nano-clusters, we simultaneously boost the efficiency and stability of formamidinium-cesium perovskite solar cells, by virtual of improved optoelectronic properties and relaxed intra-crystal strain, respectively. This device engineering, inspired and guided by atomic-scale in situ microscopic imaging, presents a new prototype for solar cell advancement. The detrimental effects of intragrain impurity nanoclusters on the efficiency and stability of perovskite solar cells remain unexplored. Here, the authors study the intragrain impurity annihilation by in situ scanning transmission electron microscopy and adopt a laser stimulus to heal such impurity.

Two‐dimensional Ruddlesden−Popper (2DRP) perovskites have attracted intense research interest for optoelectronic applications, due to their tunable optoelectronic properties and better environmental stability than their three‐dimensional counterparts. Furthermore, high‐performance photodetectors based on single‐crystal and polycrystalline thin‐films 2DRP perovskites have shown great potential for practical application. However, the complex growth process of single‐crystal membranes and uncontrollable phase distribution of polycrystalline films hinder the further development of 2DRP perovskites photodetectors. Herein, we report a series of high‐performance photodetectors based on single‐crystal‐like phase‐pure 2DRP perovskite films by designing a novel spacer source. Experimental and theoretical evidence demonstrates that phase‐pure films substantially suppress defect states and ion migration. These highly sensitive photodetectors show Ilight/Idark ratio exceeding 3 × 104, responsivities exceeding 16 A/W, and detectivities exceeding 3 × 1013 Jones, which are higher at least by 1 order than those of traditional mixed‐phase thin‐films 2DRP devices (close to the reported single‐crystal devices). More importantly, this strategy can significantly enhance the operational stability of optoelectronic devices and pave the way to large‐area flexible productions. A series of single‐crystal‐like two‐dimensional Ruddlesden−Popper perovskite thin films with more than 10 µm grain size are obtained. The photodetectors devices based on these high‐quality phase‐pure perovskite films demonstrate superior stability, high flexibility, and remarkable performance (Ilight/Idark ratio exceeding 3 × 104, responsivities exceeding 16 A/W, and detectivities exceeding 3 × 1013 Jones).

Quasi‐homojunction (QHJ) organic solar cells (OSCs) offer a promising alternative architecture that combines the advantages of bulk heterojunction (BHJ) and homojunction (HJ) designs. By blending a minimal fraction of donor material (a few wt%) into a nonfullerene acceptor matrix, QHJ devices can be designed to achieve efficient charge separation and transport while avoiding the morphological complexity and instability of BHJs. This study demonstrates that Y6‐based QHJ OSCs, incorporating only 4 wt% donor content, achieve a power conversion efficiency of 7.1%. This performance enhancement is enabled by replacing the PEDOT:PSS anode with a novel self‐assembled monolayer anode, which induces vertical phase separation, positioning the donor polymer at the anode interface to enhance charge extraction. The optimized vertical morphology not only facilitates efficient charge transport but also ensures excellent stability, maintaining consistent performance across active layer thicknesses of 55–180nm. This highlights the potential of QHJ architecture to combine the simplicity of HJ with the performance advantages of BHJ. Quasi‐homojunction (QHJ) organic solar cells combine the simplicity of homojunctions with the performance benefits of bulk heterojunctions. Using only 4 wt% donor material and a novel self‐assembled monolayer anode, Y6‐based QHJ devices achieve 7.1% efficiency. The optimized vertical phase separation enhances charge extraction and stability, offering a robust design across varying active layer thicknesses.

Metal halide perovskites, a class of cost-effective semiconductor materials, are of great interest for modern and upcoming display technologies that prioritize the light-emitting diodes (LEDs) with high efficiency and excellent color purity. The prevailing approach to achieving efficient luminescence from pervoskites is enhancing exciton binding effect and confining carriers by reducing their dimensionality or grain size. However, splitting pervoskite lattice into smaller ones generates abundant boundaries in solid films and results in more surface trap states, needing exact passivation to suppress trap-assisted nonradiative losses. Here, an ions-induced heteroepitaxial growth method is employed to assembe perovskite lattices with different structures into large-sized grains to produce lattice-anchored nanocomposites for efficient LEDs with high color purity. This approach enables the nanocomposite thin films, composed of three-dimensional (3D) CsPbBr3 and its variant of zero-dimensional (0D) Cs4PbBr6, to feature significant low trap-assisted nonradiative recombination, enhanced light out-coupling with a corrugated surface, and well-balanced charge carrier transport. Based on the resultant 3D/0D perovskite nanocomposites, we demonstrate the perovskite LEDs achieving an remarkable external quantum efficiency of 31.0% at the emission peak of 521 nm with a narrow full width at half-maximum of only 18 nm. This research introduces a novel approach to the development of well-assembled nanocomposites for perovskite LEDs, demonstrating high efficiency comparable to that of state-of-the-art organic LEDs.

The strength of evidence regarding long-term changes to fitness resulting from the coronavirus disease 2019 (COVID-19) lockdowns is deficient. This two-site retrospective study aimed to investigate the long-term changes in physical fitness among young adults a year after the onset of the pandemic using a robust historical control. University freshmen who underwent physical fitness tests in 2019 and completed a follow-up in 2020 (study group) were included. The primary focus was to compare the current cohort with a historical control group who completed the same tests a year prior (2018). A total of 5376 individuals were recruited, of which 2239 were in the study group. Compared with the control, the study group exhibited a decrease in anaerobic fitness, with an overall difference of −0.84 (95% confidence interval [CI], [−1.33 to −0.36]); declines in aerobic fitness, with a difference of −2.25 [−3.92 to −0.57] for males and −4.28 [−4.97 to −3.59] for females; a reduced explosive fitness (−2.68 [−3.24 to −2.12]); and a decreased upper-body strength in females (−1.52 [−2.16 to −0.87]). The fitness of young adults has been considerably compromised by COVID-19 lockdowns, highlighting the importance of promoting physical activity to prevent long-term health implications.

Switching to normal diet (ND) is the regular therapy for high-fat diet (HFD)-induced nonalcoholic fatty liver disease (NAFLD). Intermittent fasting (IF) is a unique treatment which may exhibits better therapeutic efficacy. Thus, we aim to investigate the therapeutic effects of these treatments and exploring the mechanisms. In the present study, NAFLD mouse model was induced by a 10-week HFD. Thereafter, mice adopted continued HFD, ND, or IF for the next 12 weeks. Finally, the liver was then harvested to assess lipid deposition, lipid metabolism, apoptosis, and autophagy, while blood was collected to determine blood glucose and insulin. The results showed that IF and ND treatment improved lipid deposition and metabolic disorder of NAFLD mice; the increasing body weight, liver weight, and HOMA-IR index of HFD mice were also alleviated by IF and ND. Furthermore, IF and ND treatment activated the macrophage migration inhibitory factor (MIF)/AMPK pathway and regulated its downstream autophagy and apoptosis. However, the efficacy of IF was better than ND. Both IF and ND activates MIF signaling and alleviate the lipotoxicity of NAFLD while IF therapy is more effective than ND. The different MIF up-regulation might be the underlying mechanism of why IF benefits more than ND.

It is a daunting challenge to measure the concentration of each component in natural gas, because different components in mixed gas have cross-sensitivity for a single sensor. We have developed a mixed gas identification device based on a neural network algorithm, which can be used for the online detection of natural gas. The neural network technology is used to eliminate the cross-sensitivity of mixed gases to each sensor, in order to accurately recognize the concentrations of methane, ethane and propane, respectively. The neural network algorithm is implemented by a Field-Programmable Gate Array (FPGA) in the device, which has the advantages of small size and fast response. FPGAs take advantage of parallel computing and greatly speed up the computational process of neural networks. Within the range of 0–100% of methane, the test error for methane and heavy alkanes such as ethane and propane is less than 0.5%, and the response speed is several seconds.