Room Temperature Crystallized Phase-Pure α-FAPbI3 Perovskite with In-Situ Grain-Boundary Passivation.

Energy loss in perovskite grain boundaries (GBs) is a primary limitation toward high-efficiency perovskite solar cells (PSCs). Two critical strategies to address this issue are high-quality crystallization and passivation of GBs. However, the established methods are generally carried out discretely due to the complicated mechanisms of grain growth and defect formation. In this study, a combined method is proposed by introducing 3,4,5-Trifluoroaniline iodide (TFAI) into the perovskite precursor. The TFAI triggers the union of nano-sized colloids into microclusters and facilitates the complete phase transition of α-FAPbI3 at room temperature. The controlled chemical reactivity and strong steric hindrance effect enable the fixed location of TFAI and suppress defects at GBs. This combination of well-crystallized perovskite grains and effectively passivated GBs leads to an improvement in the open circuit voltage (Voc ) of PSCs from 1.08 V to 1.17 V, which is one of the highest recorded Voc without interface modification. The TFAI-incorporated device achieved a champion PCE of 24.81%. The device maintained a steady power output near its maximum power output point, showing almost no decay over 280 h testing without pre-processing.

Optoelectronic synapses based on a triple cation perovskite and Al/MoO3 interface for neuromorphic information processing.

Optoelectronic synaptic transistors are attractive for applications in next-generation brain-like computation systems, especially for their visible-light operation and in-sensor computing capabilities. However, from a material perspective, it is difficult to build a device that meets expectations in terms of both its functions and power consumption, prompting the call for greater innovation in materials and device construction. In this study, we innovatively combined a novel perovskite carrier supply layer with an Al/MoO3 interface carrier regulatory layer to fabricate optoelectronic synaptic devices, namely Al/MoO3/CsFAMA/ITO transistors. The device could mimic a variety of biological synaptic functions and required ultralow-power consumption during operation with an ultrafast speed of >0.1 µs under an optical stimulus of about 3 fJ, which is equivalent to biological synapses. Moreover, Pavlovian conditioning and visual perception tasks could be implemented using the spike-number-dependent plasticity (SNDP) and spike-rate-dependent plasticity (SRDP). This study suggests that the proposed CsFAMA synapse with an Al/MoO3 interface has the potential for ultralow-power neuromorphic information processing.

Intermediate Phase Free α-FAPbI3 Perovskite via Green Solvent Assisted Perovskite Single Crystal Redissolution Strategy.

Perovskite single-crystal redissolution (PSCR) strategy is highly desired for efficient formamidinium lead triiodide (FAPbI3 ) perovskite photovoltaics with enhanced phase purity, improved film quality, low trap-state density, and good stability. However, the phase transition and crystallization dynamics of FAPbI3 remain unclear in the PSCR process compared to the conventional fabrication from the mixing of precursor materials. In this work, a green-solvent-assisted (GSA) method is employed to synthesize centimeter-sized α-FAPbI3 single crystals, which serve as the high-purity precursor to fabricate perovskite films. The α-FAPbI3 PSCR strategy facilitates direct α-phase formation and inhibits the complex intermediate phases monitored by in situ grazing-incidence wide-angle X-ray scattering. Moreover, the α-phase stability is prolonged due to the relaxation of the residual lattice strain through the isotropic orientation phase growth. Consequently, the GSA-assisted PSCR strategy effectively promotes crystallization and suppresses non-radiative recombination in perovskite solar cells, which boosts the device efficiency from 22.08% to 23.92% with significantly enhanced open circuit voltage. These findings provide deeper insight into the PSCR process in terms of its efficacy in phase formation and lattice strain release. The green low-cost solvent may also offer a new and ideal solvent candidate for large-scale production of perovskite photovoltaics.

Green Solvent Polishing Enables Highly Efficient Quasi-2D Perovskite Solar Cells.

Preferred crystalline orientation at the surface of quasi-2D organic-inorganic halide perovskites is crucial to promote vertical carrier transport and interface carrier extraction, which further contribute to device efficiency and stability in photovoltaic applications. However, loose unoriented and defective surfaces are inevitably formed in the crystallization process, especially with the introduction of bulky organic cations into the quasi-2D perovskites. Here, a facile and effective surface polishing method using a natural-friendly green solvent, 2,2,2-trifluoroethanol, is proposed to reconstruct the surface. After solvent polishing, the randomly oriented phases containing trap sites on the surface are successfully removed, and the compact vertical-oriented phases underneath are revealed with less defectiveness and better smoothness, which greatly facilitates carrier transport and interfacial charge extraction. Consequently, the green solvent polished devices show a boosting efficiency of 18.38% with a high open-circuit voltage of 1.21 V. The devices also show improved storage and operational stability.

Highly Efficient and Stable Self-Powered Mixed Tin-Lead Perovskite Photodetector Used in Remote Wearable Health Monitoring Technology.

Realization of remote wearable health monitoring (RWHM) technology for the flexible photodiodes is highly desirable in remote-sensing healthcare systems used in space stations, oceans, and forecasting warning, which demands high external quantum efficiency (EQE) and detectivity in NIR region. Traditional inorganic photodetectors (PDs) are mechanically rigid and expensive while the widely reported solution-processed mixed tin-lead (MSP) perovskite photodetectors (PPDs) exhibit a trade-off between EQE and detectivity in the NIR region. Herein, a novel functional passivating antioxidant (FPA) strategy has been introduced for the first time to simultaneously improve crystallization, restrain Sn2+ oxidization, and reduce defects in MSP perovskite films by multiple interactions between thiophene-2-carbohydrazide (TAH) molecules and cations/anions in MSP perovskite. The resultant solution-processed rigid mixed Sn-Pb PPD simultaneously achieves high EQE (75.4% at 840 nm), detectivity (1.8 × 1012 Jones at 840 nm), ultrafast response time (trise /tfall = 94 ns/97 ns), and improved stability. This work also highlights the demonstration of the first flexible photodiode using MSP perovskite and FPA strategy with remarkably high EQE (75% at 840 nm), and operational stability. Most importantly, the RWHM is implemented for the first time in the PIN MSP perovskite photodiodes to remotely monitor the heart rate of humans at rest and after-run conditions.

Strain Release and Defect Passivation in Formamidinium-Dominated Perovskite via a Novel in-Plane Thermal Gradient Assisted Crystallization Strategy.

It is essential to release annealing induced strain during the crystallization process to realize efficient and stable perovskite solar cells (PSCs), which does not seem achievable using the conventional annealing process. Here we report a novel and facile thermal gradient assisted crystallization strategy by simply introducing a slant angle between the preheated hot plate and the substrate. A distinct crystallization sequence resulted along the in-plane direction pointing from the hot side to the cool side, which effectively reduced the crystallization rate, controlled the perovskite grain growth, and released the in-plane tensile strain. Moreover, this strategy enabled uniform strain distribution in the vertical direction and assisted in reducing the defects and aligning the energy bands. The corresponding device demonstrated champion power conversion efficiencies (PCEs) of 23.70% and 21.04% on the rigid and flexible substrates, respectively. These highly stable rigid devices retained 97% of the initial PCE after 1097 h of storage and more than 80% of the initial PCE after 1000 h of continuous operation at the maximum power point. This novel strategy opens a simple and effective avenue to improve the quality of perovskite films and photovoltaic devices via strain modulation and defect passivation.

Dynamic algorithm for fitness function greatly improves the optimization efficiency of frequency selective surface for better design of radar.

Multiple objectives optimization of frequency selective surface (FSS) structures is challenging in electromagnetic wave filter design. For example, one of the sub-objectives, the sidelobe level (SLL), is critical to directional anti-interference, which is complicated and becomes the bottleneck for radar design. Here, we established a dynamic algorithm for fitness function to automatically adjust the weights of multiple objectives in the optimization process of FSS structures. The dynamic algorithm could efficiently evaluate the achieving probability of sub-objectives according to the statistical analysis of the latest individual distribution so that the fitness function could automatically adjusted to focus on the sub-objective difficult to optimize, such as SLL. Computational results from the dynamic algorithm showed that the efficiency of multi-objective optimization was greatly improved by 213%, as compared to the fixed-weighted algorithm of the fitness function. Specifically for SLL, the efficiency rate increased even better, up to 315%. More interestingly, the FSS structures were most improved while picking median value or golden section value as the reference value. Taken together, the current study indicated that the dynamic algorithm with fitness function might be a better choice for FSS structural optimization with SLL suppression and potentially for the better design of lower SLL radar.

New Lead-free Organic-Inorganic Hybrid Semiconductor Single Crystals for a UV-Vis-NIR Broadband Photodetector.

Organic-inorganic hybrid semiconducting (OIHS) materials, which can detect broader spectral regions, are highly desired in several applications including biomedical imaging, night vision, and optical communications. Although lead (Pb)-halide perovskites have reached a mature research stage, high toxicity of Pb hinders their large-scale viability. Tin (Sn)-based perovskites are the most common OIHS broadband light absorbers that replace toxic Pb; however, they are extremely unstable due to the notorious Sn2+ oxidation. Herein, a novel, non-toxic, and solution-processed millimeter-sized OIHS single crystal [Ga(C3H7NO)6](I3)3 has been grown at room temperature. Both the absorption measurement and density functional theory calculations have confirmed a narrow indirect band gap of 1.32 eV. The corresponding photodetector based on this single crystal demonstrated excellent performance including an ultraviolet-visible-near infrared (UV-vis-NIR) response between 325 and 1064 nm, fast response time (trise/tdecay = 3.8 ms/5.4 ms), and profound air storage stability (41 h), thus outperforming most common photodetectors based on Sn-based perovskites. This work not only provides a profound understanding of this novel organic-inorganic single-crystal material but also demonstrates its great potential to realize the high-performance UV-vis-NIR broadband photodetectors.

Data-driven design of high-performance MASnxPb1-xI3 perovskite materials by machine learning and experimental realization.

The photovoltaic performance of perovskite solar cell is determined by multiple interrelated factors, such as perovskite compositions, electronic properties of each transport layer and fabrication parameters, which makes it rather challenging for optimization of device performances and discovery of underlying mechanisms. Here, we propose and realize a novel machine learning approach based on forward-reverse framework to establish the relationship between key parameters and photovoltaic performance in high-profile MASnxPb1-xI3 perovskite materials. The proposed method establishes the asymmetrically bowing relationship between band gap and Sn composition, which is precisely verified by our experiments. Based on the analysis of structural evolution and SHAP library, the rapid-change region and low-bandgap plateau region for small and large Sn composition are explained, respectively. By establishing the models for photovoltaic parameters of working photovoltaic devices, the deviation of short-circuit current and open-circuit voltage with band gap in defective-zone and low-bandgap-plateau regions from Shockley-Queisser theory is captured by our models, and the former is due to the deep-level traps formed by crystallographic distortion and the latter is due to the enhanced susceptibility by increased Sn4+ content. The more difficulty for hole extraction than electron is also concluded in the models and the prediction curve of power conversion efficiency is in a good agreement with Shockley-Queisser limit. With the help of search and optimization algorithms, an optimized Sn:Pb composition ratio near 0.6 is finally obtained for high-performance perovskite solar cells, then verified by our experiments. Our constructive method could also be applicable to other material optimization and efficient device development.

Discovery of Lead-Free Perovskites for High-Performance Solar Cells via Machine Learning: Ultrabroadband Absorption, Low Radiative Combination, and Enhanced Thermal Conductivities.

Exploring lead-free candidates and improving efficiency and stability remain the obstacle of hybrid organic-inorganic perovskite-based devices commercialization. Traditional trial-and-error methods seriously restrict the discovery especially for large search space, complex crystal structure and multi-objective properties. Here, the authors propose a multi-step and multi-stage screening scheme to accelerate the discovery of hybrid organic-inorganic perovskites A2 BB'X6 from a large number of candidates through combining machine learning with high-throughput calculations for pursuing excellent efficiency and thermal stability in solar cells. Followed by a series of screenings, the structure-property relationships mapping A2 BB'X6 properties are built and the predictions are close to reported experimental results. Successfully, four experimental-feasibly candidates with good stability, high Debye temperature and suitable band gap are screened out and further verified by density-functional theory calculations, in which the predicted efficiency for three lead-free candidates ((CH3 NH3 )2 AgGaBr6 , (CH3 NH3 )2 AgInBr6 and (C2 NH6 )2 AgInBr6 ) achieves 20.6%, 19.9% and 27.6% due to ultrabroadband absorption region ranging from UVC to IRC with excitonic radiative combination rates as low as 10 ps, large or intermediate polarons form with properties similar to CH3 NH3 PbI3 and the calculated thermal conductivities are 5.04, 4.39 and 5.16 Wm-1 K-1 , respectively, with Debye temperatures larger than 500 K, beneficial for suppression of both nonradiative combination and heat-induced degradation.

Eradicating the Roots: Advanced Therapeutic Approaches Targeting Breast Cancer Stem Cells.

Accumulating evidences have demonstrated that the existence of breast cancer-initiating cells, which drives the original tumorigenicity, local invasion and migration propensity of breast cancer. These cells, termed as breast cancer stem cells (BCSCs), possess properties including self-renewal, multidirectional differentiation and proliferative potential, and are believed to play important roles in the intrinsic drug resistance of breast cancer. One of the reasons why BCBCs cause difficulties in breast cancer treating is that BCBCs can control both genetic and non-genetic elements to keep their niches safe and sound, which allows BCSCs for constant self-renewal and differentiation. Therapeutic strategies designed to target BCSCs may ultimately result in effective interventions for the treatment of breast cancer. Novel strategies including nanomedicine, oncolytic virus therapy, immunotherapy and induced differentiation therapy are emerging and proved to be efficient in anti-BCSCs therapy. In this review, we summarized breast tumor biology and the current challenges of breast cancer therapies, focused on breast cancer stem cells, and introduced promising therapeutic strategies targeting BCSCs.

Wellbore stability evaluation method based on the continuous tangent envelope of a Mohr circle.

It is of great practical significance to accurately obtain formation collapse pressure and determine an effective three-pressure profile with a correct strength criterion in the drilling process to identify the best drilling fluid density. Taking the tight sandstone of the XuJiahe formation as an example, we conducted a series of rock mechanics tests, focusing on large-scale, high-density confining pressure triaxial experiments; determined a mathematical expression for the continuous tangent envelope of a nonlinear Mohr circle envelope based on a series of triaxial tests; and clarified the variation rules of cohesion force and internal friction angle with confining pressure. The impact of rock mechanics parameters determined by using the traditional method and the continuous tangent envelope method on wellbore stability is compared and analyzed by using the MathCAD program, and then the collapse pressure is obtained. The results show that the parabolic curve derived from the uniaxial rock mechanics test data of the XuJiahe formation is not suitable for the triaxial test results under high confining pressure. By means of the continuous tangent envelope method, the relationship between rock cohesion and internal friction angle and confining pressure is obtained; this replaces the traditional collapse pressure calculation results using geophysical logging data or uniaxial tests, and the relationship between cohesion and friction angle is more consistent with confining pressure. The MathCAD simulation analysis shows that the rock mechanics parameters determined by the continuous tangent envelope can reflect the stratum situation more truly than the linear envelope method. Compared with the linear envelope method and parabolic envelope method under the same conditions, the continuous tangent envelope method has certain advantages in determining the critical density, which provides a theoretical basis for the accuracy of sandstone formation collapse pressure calculation and can give significant guidance for the study of wellbore stability of deep sandstone formations.