Ions-induced Epitaxial Growth of Perovskite Nanocomposites for Highly Efficient Light-Emitting Diodes with EQE Exceeding 30%

Cesium lead bromide (CsPbBr3) is a widely used emitter for perovskite light-emitting diodes (PeLEDs), benefiting from its large carrier mobility, high color purity and good thermal stability. However, the three-dimensional CsPbBr3 films encounter challenges due to their massive intrinsic defects and weak exciton binding effect, which limited their electroluminescence efficiency. To address this issue, the prevailing approach is to confine carriers by reducing dimensionality or size. Nonetheless, this method results in an increase in surface trap states due to the larger surface-to-volume ratio and presents difficulties in carrier injection and transport after reducing lattice splitting to smaller sizes. Here, we successfully achieved proper control over film crystallization by introducing sodium ions, which facilitate the epitaxial growth of zero-dimensional Cs4PbBr6 on the surface of CsPbBr3, forming large grain matrixes where CsPbBr3 is encapsulated by Cs4PbBr6. Notably, the ions-induced epitaxial growth enables the CsPbBr3 emitter with significantly reduced trap states, and generates coarsened nanocomposites of CsPbBr3&Cs4PbBr6 with grain size that surpass the average thickness of the thin perovskite film, resulting in a wavy surface conducive to light out-coupling. Additionally, another additive of formamidinium chloride was incorporated to assist the growth of nanocomposites with larger size and lower defects as well as better carrier injection and transportation. As a result, our demonstrated PeLEDs based on the coarsened nanocomposites exhibit low nonradiative recombination, enhanced light extraction and well-balanced carrier transportation, leading to high-performance devices. The champion device achieved an external quantum efficiency of 31.0% at the emission peak of 521 nm with a narrow full width at half-maximum (FWHM) of 18 nm

Charge-carrier balance for highly efficient inverted planar heterojunction perovskite solar cells

The charge-carrier balance strategy by interface engineering is employed to optimize the charge-carrier transport in inverted planar heterojunction perovskite solar cells. N,N-Dimethylformamide-treated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and poly(methyl methacrylate)-modified PCBM are utilized as the hole and electron selective contacts, respectively, leading to a high power conversion efficiency of 18.72%

Intragrain impurity annihilation for highly efficient and stable perovskite solar cells

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

Limitations and solutions for achieving high-performance perovskite tandem photovoltaics

The large light absorption coefficient, long carrier diffusion length, and high defect tolerance enable organic-inorganic lead halide perovskites for excellent photovoltaic performance. The highest certified power conversion efficiency of single-junction perovskite solar cells (PSCs) has reported 25.5%. Besides, the bandgap of perovskites can be tuned by engineering their composition. These merits have made perovskites promising candidates for tandem photovoltaics, which can cross over the Shockley-Queisser limit of single-junction PSCs with economic costs. However, there are yet some hurdles in the wide-bandgap and narrow-bandgap subcells as well as interconnected layers (ICLs), which limit the commercial applications of perovskite tandem solar cells (PTSCs). In this review, we summarize the major scientific and technical limitations of PTSCs. We firstly demonstrate the configurations and working principles of PTSCs. Then, the developments of front subcells and rear subcells are discussed. Their main drawbacks, implemented technologies, and underlying mechanisms are analyzed in detail. Subsequently, the progress of ICLs which are responsible for guaranteeing continuous current in 2 T PTSCs are discussed. In addition, the stability of PTSCs is also summarized. The purpose of this review is to map and thrive the future development of PTSCs

Mixed Natural Gas Online Recognition Device Based on a Neural Network Algorithm Implemented by an FPGA

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

Flattening Grain Boundary Grooves for Perovskite Solar Cells with High Optomechanical Reliability

Optomechanical reliability has emerged as an important criterion for evaluating the performance and commercialization potential of perovskite solar cells (PSCs) due to the mechanical property mismatch of metal halide perovskites with other device layer. In this work, grain boundary grooves, a rarely discussed film microstructural characteristic, are found to impart significant effects on the optomechanical reliability of perovskite substrate heterointerfaces and thus PSC performance. By pre burying iso butylammonium chloride additive in the electron transport layer (ETL), GB grooves (GBGs) are flattened and an optomechanically reliable perovskite heterointerface that resists photothermal fatigue is created. The improved mechanical integrity of the ETL perovskite heterointerfaces also benefits the charge transport and chemical stability by facilitating carrier injection and reducing moisture or solvent trapping, respectively. Accordingly, high performance PSCs which exhibit efficiency retentions of 94.8% under 440 h damp heat test (85% RH and 85 degrees C), and 93.0% under 2000 h continuous light soaking are achieved

The long-term impact of the COVID-19 pandemic on physical fitness in young adults: a historical control study

Abstract 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

Charge-Carrier Balance for Highly Efficient Inverted Planar Heterojunction Perovskite Solar Cells

The charge-carrier balance strategy by interface engineering is employed to optimize the charge-carrier transport in inverted planar heterojunction perovskite solar cells. N,N-Dimethylformamide-treated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and poly(methyl methacrylate)-modified PCBM are utilized as the hole and electron selective contacts, respectively, leading to a high power conversion efficiency of 18.72%

Dual-Source Precursor Approach for Highly Efficient Inverted Planar Heterojunction Perovskite Solar Cells

The highest efficiencies reported for perovskite solar cells so far have been obtained mainly with methylammonium and formamidinium mixed cations. Currently, high-quality mixed-cation perovskite thin films are normally made by use of antisolvent protocols. However, the widely used “antisolvent”-assisted fabrication route suffers from challenges such as poor device reproducibility, toxic and hazardous organic solvent, and incompatibility with scalable fabrication process. Here, a simple dual-source precursor approach is developed to fabricate high-quality and mirror-like mixed-cation perovskite thin films without involving additional antisolvent process. By integrating the perovskite films into the planar heterojunction solar cells, a power conversion efficiency of 20.15% is achieved with negligible current density–voltage hysteresis. A stabilized power output approaching 20% is obtained at the maximum power point. These results shed light on fabricating highly efficient perovskite solar cells via a simple process, and pave the way for solar cell fabrication via scalable methods in the near future

Towards simplifying the device structure of high-performance perovskite solar cells

Perovskite solar cells (PSCs) are considered one of the most promising next-generation examples of high-tech photovoltaic energy converters, as they possess an unprecedented power conversion efficiency with low cost. A typical high-performance PSC generally contains a perovskite active layer sandwiched between an electron-transport layer (ETL) and a hole-transport layer (HTL). The ETL and HTL contribute to the charge extraction in the PSC. However, these additional two layers complicate the manufacturing process and raise the cost. To extend this technology for commercialization, it is highly desired that the structure of PSCs is further simplified without sacrificing their photovoltaic performances. Thus, ETL-free or/and HTL-free PSCs are developed and attract more and more interest. Herein, the commonly used methods in reducing the defect density and optimizing the energy levels in conventional PSCs in order to simplify their structures are summarized. Then, the development of diverse ETL-free or/and HTL-free PSCs is discussed, with the PSCs classified, including their working principles, implemented technologies, remaining challenges, and future perspectives. The aim is to redirect the way toward low-cost and high-performance PSCs with the simplest possible architecture