Regulating Surface Defects to Achieve More Positive Light Soaking Effect in Perovskite Solar Cells.

The dynamic defect tolerance under light soaking is a crucial aspect of halide perovskites. However, the underlying physics of light soaking remains elusive and is subject to debate, exhibiting both positive and negative effects. In this investigation, we demonstrated that surface defects in perovskite films significantly impact the performance and stability of perovskite solar cells, closely correlated with light soaking behaviors. Removing the top surface layer through adhesive tape, the surface defect density noticeably decreases, leading to enhanced photoluminescence (PL) efficiency, prolonged carrier lifetime, and higher conductivity. Consequently, the power conversion efficiency (PCE) of solar cells improves from 17.70% to 20.5%. Furthermore, we confirmed a positive correlation between surface defects and the light soaking effect. Perovskite films with low surface defects surprisingly exhibit a 3-fold increase in PL intensity and an 85% increase in carrier lifetime under 500 s of continuous illumination at an intensity of 100 mW/cm2. Beyond the conventional strategy of suppressing defect trapping, we propose increasing the capability of dynamic defect tolerance as an effective strategy to enhance the optoelectronic properties and performance of perovskite solar cells.

Can thick metal-halide perovskite single crystals have narrower optical bandgaps with near-infrared absorption?

Metal-halide perovskite (MHP) single crystals are emerging as potential competitors to their polycrystalline thin-film counterparts. These materials have shown the specific feature of extended absorbance towards the near-infrared (NIR) region, which promises further extension of their applications in the field of photovoltaics and photodetectors. This notable expansion of absorbance has been explained by the narrower effective optical bandgap of MHP single crystals promoted by their large thickness over several micrometres to millimetres. Herein, the attributes of the material's thickness and the measurement technique used to estimate these characteristics are discussed to elucidate the actual origins of the extended absorbance of MHP single crystals. Contrary to the general belief of the narrower bandgap of the MHP single crystals, we demonstrate that the extended NIR absorption in the MHP single crystals mainly originates from the combination of unique below-bandgap absorption of MHPs, the thickness of single crystals, and the technical limitation of the spectrophotometer, with the key attributes of (i) significantly large thickness of the MHP single crystals by suppressing the transmitted light and (ii) the detector's limited dynamic range. Combining the theoretical and experimental characterizations, we clarify the significant role of the large thickness together with the limited sensitivity of the detector in promoting the well-known red shift of the absorption onset of the MHP single crystals. The observations evidently show that in some special circumstances, the acquired absorption spectrum cannot reliably represent the optical bandgap of MHP materials. This highlights some misinterpretations in the estimation of the narrower optical bandgap of the MHP single crystals from conventional optical methods, while the optical bandgap is an inherent property independent of the thickness. The proposed broad applications of the MHP single crystals are dictated by their fascinating properties, and therefore, a deep insight into these features should be considered besides device applications, because much of their property-function relationships are still ambiguous and a subject of debate.

Interfacial alloying between lead halide perovskite crystals and hybrid glasses.

The stellar optoelectronic properties of metal halide perovskites provide enormous promise for next-generation optical devices with excellent conversion efficiencies and lower manufacturing costs. However, there is a long-standing ambiguity as to whether the perovskite surface/interface (e.g. structure, charge transfer or source of off-target recombination) or bulk properties are the more determining factor in device performance. Here we fabricate an array of CsPbI3 crystal and hybrid glass composites by sintering and globally visualise the property-performance landscape. Our findings reveal that the interface is the primary determinant of the crystal phases, optoelectronic quality, and stability of CsPbI3. In particular, the presence of a diffusion "alloying" layer is discovered to be critical for passivating surface traps, and beneficially altering the energy landscape of crystal phases. However, high-temperature sintering results in the promotion of a non-stoichiometric perovskite and excess traps at the interface, despite the short-range structure of halide is retained within the alloying layer. By shedding light on functional hetero-interfaces, our research offers the key factors for engineering high-performance perovskite devices.

Effective Suppressing Phase Segregation of Mixed-Halide Perovskite by Glassy Metal-Organic Frameworks.

Lead mixed-halide perovskites offer tunable bandgaps for optoelectronic applications, but illumination-induced phase segregation can quickly lead to changes in their crystal structure, bandgaps, and optoelectronic properties, especially for the Br-I mixed system because CsPbI3 tends to form a non-perovskite phase under ambient conditions. These behaviors can impact their performance in practical applications. By embedding such mixed-halide perovskites in a glassy metal-organic framework, a family of stable nanocomposites with tunable emission is created. Combining cathodoluminescence with elemental mapping under a transmission electron microscope, this research identifies a direct relationship between the halide composition and emission energy at the nanoscale. The composite effectively inhibits halide ion migration, and consequently, phase segregation even under high-energy illumination. The detailed mechanism, studied using a combination of spectroscopic characterizations and theoretical modeling, shows that the interfacial binding, instead of the nanoconfinement effect, is the main contributor to the inhibition of phase segregation. These findings pave the way to suppress the phase segregation in mixed-halide perovskites toward stable and high-performance optoelectronics.

Fabrication and Characterization of 2D Layered Perovskites with a Gradient Band Gap.

Vertical gradient band-gap heterostructures of two-dimensional (2D) layered perovskites have attracted considerable research interest due to their superior optoelectronic properties and demonstrated potential for use in optical devices. However, its fabrication has been challenging. In this investigation, 2D Ruddlesden-Popper mixed halide perovskite single crystals with a vertical gradient band gap were synthesized by using a solid-state halide diffusion process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements after diffusion confirm that the crystalline and morphology remain intact. The transmittance and photoluminescence (PL) spectra show the formation of a vertical gradient band gap that is ascribed to gradient halide distribution through halide intermixing. The mixed halide crystal exhibits high stability with completely suppressed phase segregation in the time-dependent PL measurement. The time-resolved photoluminescence (TRPL) spectra prove that the mixed halide sample has an enhanced carrier transport due to the Förster resonance energy transfer (FRET) effect. Besides, the halide diffusion behavior is found to be different from the previously proposed "layer-by-layer" diffusion model in exfoliated crystals. The gradient band-gap structure is critical for various applications in which vertical carrier transport is demanded.

Controllable Acceleration and Deceleration of Charge Carrier Transport in Metal-Halide Perovskite Single-Crystal by Cs-Cation Induced Bandgap Engineering.

Charge carrier transport in materials is of essential importance for photovoltaic and photonic applications. Here, the authors demonstrate a controllable acceleration or deceleration of charge carrier transport in specially structured metal-alloy perovskite (MACs)PbI3 (MA= CH3 NH3 ) single-crystals with a gradient composition of CsPbI3 /(MA1- x Csx )PbI3 /MAPbI3 . Depending on the Cs-cation distribution in the structure and therefore the energy band alignment, two different effects are demonstrated: i) significant acceleration of electron transport across the depth driven by the gradient band alignment and suppression of electron-hole recombination, benefiting for photovoltaic and detector applications; and ii) decelerated electron transport and thus improved radiative carrier recombination and emission efficiency, highly beneficial for light and display applications. At the same time, the top Cs-layer results in hole localization in the top layer and surface passivation. This controllable acceleration and deceleration of electron transport is critical for various applications in which efficient electron-hole separation and suppressed nonradiative electron-hole recombination is demanded.

A prophylactic effect of local vibration on quadriceps muscle fatigue in non-athletic males: a randomized controlled trial study.

[Purpose] This study was conducted to investigate the immediate prophylactic effects of local vibration on quadriceps muscle fatigue in young non-athletic males. [Participants and Methods] Thirty healthy young males were randomly assigned to vibration and sham control groups. Participants in the local vibration group received a single session vibration (2 minutes, 30 Hz). They also in the control group received a 2-minute vibration, while the vibration system was off. MVC, RMS and median frequency of EMG findings and time to reach fatigue were measured. [Results] Time to reach fatigue and MVC in the local vibration group was significantly high than those in the sham control group. [Conclusion] It seems that the prior local muscle vibration may be useful to attenuate some signs and symptoms of muscle fatigue.

The effect of functional stretching exercises on functional outcomes in spastic stroke patients: A randomized controlled clinical trial.

BACKGROUND: Stroke is the biggest cause of disability in adults. Spasticity is a primary impairment of stroke with a highly variable prevalence. In the present research, we aimed to determine the impact of functional stretching exercises on functional outcomes in stroke patients. METHODS: Thirty stroke patients were randomized into two groups-Experimental group and control group for the purposes of the study. The subjects in the experimental group participated in a functional stretching training program at the rehabilitation center thrice a week for four weeks. The subjects in both groups were evaluated in 3 intervals, once at baseline, once at the end of the program, and once at 2 months following the program. Clinical assessments, such as measuring spasticity, were conducted using the Modified Modified Ashworth Scale (MMAS). Functional outcomes were also evaluated, using the Timed Up and Go (TUG) test, as well as the Timed 10-Meter Walk Test (WTT). Friedman test in SPSS version 22.0 was used to analysis the response variables with respect to each stage of evaluation. Spearman rank correlation was also used to measure correlation among clinical assessments and functional outcomes. RESULTS: The comparison between two groups showed significant differences only in the Modified Modified Ashworth Scale and Visual Analogue Scale (VAS) post treatment. The experimental group showed significant differences in the MMAS (p = 0.002), WTT (p < 0.001), and TUG (p < 0.001) scores. Nevertheless, the scores of the control group were not significantly different in different stages of evaluation. CONCLUSION: The findings of the study suggest that using functional stretching exercises can improve functional outcomes in chronic spastic stroke patients.

The Effect of Functional Stretching Exercises on Neural and Mechanical Properties of the Spastic Medial Gastrocnemius Muscle in Patients with Chronic Stroke: A Randomized Controlled Trial.

BACKGROUND: Following spasticity, neural and mechanical changes of the paretic muscle often occur, which affect the muscle function. The aim of this study was to investigate the effect of functional stretching exercises on neural and mechanical properties of the spastic muscle in patients with stroke. MATERIALS AND METHODS: This study was a single-blinded, randomized control trial. Forty five patients with stroke (experimental group: n = 30; control group: n = 15) participated in this study. Subjects in the experimental group participated in a functional stretching program 3 times a week for 4 weeks. Subjects in both groups were evaluated before the training, at the end of training, and then during a 2-month follow-up. Neural properties, including H-reflex latency and Hmax/Mmax ratio, were acquired. Mechanical properties, including fascicle length, pennation angle, and muscle thickness in the spastic medial gastrocnemius muscle, were evaluated. Repeated measure analysis of variance was used in the analysis. RESULTS: Time by group interaction in the pennation angle (P = .006), and in muscle thickness (P = .030) was significant. The results indicated that the H-reflex latency (P = .006), pennation angle (P < .001), and muscle thickness (P = .001) were altered after stretching training program and these changes were at significant level after 2-month follow-up. CONCLUSION: The results indicated that the use of functional stretching exercises can cause significant differences in neural and mechanical properties of spastic medial gastrocnemius muscle in patients with chronic stroke.

Electromyographic changes in muscles around the ankle and the knee joints in women accustomed to wearing high-heeled or low-heeled shoes.

OBJECTIVES: This study aimed to investigate muscle activities in the muscles around the ankle and knee joints in women accustomed to wearing high-heeled or low-heeled shoes. METHODOLOGY: Forty young women (age: 18-40 years) participated in this comparative clinical study. Twenty of the recruited subjects were accustomed to high-heeled shoes and the other half to low-heeled shoes. Electrical activities of the ankle and knee muscles in both groups with and without wearing their accustomed shoes were studied during walking. RESULTS: Tibialis anterior and the medial gastrocnemius muscles started contraction earlier in the high-heeled shoe group. The duration of medial gastrocnemius activity and the intensity of proneus longus activity were significantly more in the high-heeled shoe group. CONCLUSION: Wearing high-heeled shoe for a long time could result in over work of muscles such as medial gastrocnemius and proneus longus by increasing the duration or the intensity of their contractions during walking.

Immediate effect of common peroneal nerve electrical stimulation on quadriceps muscle arthrogenic inhibition in patients with knee osteoarthritis.

OBJECTIVE: To investigate the immediate effect of electrical stimulation of the common peroneal nerve on the maximum voluntary activation of the quadriceps muscle in patients with knee osteoarthritis. METHODOLOGY: Fifteen subjects with knee osteoarthritis (mean age: 50.5 ± 13 years) participated in this study. To measure the arthrogenic inhibition ratio of quadriceps, a burst of electrical stimulation was superimposed on the maximum voluntary contraction, and the percentage of change in the force production was computed. The same measurement was also performed with concurrent electrical stimulation of the common peroneal nerve. RESULTS: All the patients with knee osteoarthritis showed significant arthrogenic inhibition of the quadriceps muscle. The stimulation of the common peroneal nerve was able to reduce this inhibition and increase the capacity of the muscle to produce a significantly higher knee extension force (p = 0.028). CONCLUSIONS: Electrical stimulation of the common peroneal nerve concurrent with the maximum voluntary effort can remove the arthrogenic inhibition of the quadriceps muscle in patients with knee osteoarthritis. This finding could have clinical implications in the management of patients with knee disorders.

Factors affecting job motivation among health workers: a study from Iran.

OBJECTIVE: Human resources are the most vital resource of any organizations which determine how other resources are used to accomplish organizational goals. This research aimed to identity factors affecting health workers' motivation in Shahid Beheshti University of Medical Sciences (SBUMS). METHOD: This is a cross-sectional survey conducted with participation of 212 health workers of Tehran health centers in November and December 2011. The data collection tool was a researcher-developed questionnaire that included 17 motivating factors and 6 demotivating factors and 8 questions to assess the current status of some factors. Validity and reliability of the tool were confirmed. Data were analyzed with descriptive and analytical statistical tests. RESULTS: The main motivating factors for health workers were good management, supervisors and managers' support and good working relationship with colleagues. On the other hand, unfair treatment, poor management and lack of appreciation were the main demotivating factors. Furthermore, 47.2% of health workers believed that existing schemes for supervision were unhelpful in improving their performance. CONCLUSIONS: Strengthening management capacities in health services can increase job motivation and improve health workers' performance. The findings suggests that special attention should be paid to some aspects such as management competencies, social support in the workplace, treating employees fairly and performance management practices, especially supervision and performance appraisal.

The effects of triceps surae fatigue on the torque and electromyographic parameters in athletes compared with non-athletes.

BACKGROUND AND OBJECTIVES: The common description of muscular fatigue is the failure of muscle in maintaining a target force. Even in sustained contraction, when muscle force is held at a stable level, physiological, biomechanical and electromyographic changes can occur. The purpose of this study is to compare the effects of triceps surae (TS) fatigue on the torque, falling slope and electromyographic (EMG) parameters between athletes and non-athletes. MATERIALS AND METHODS: Nineteen healthy women (10 non-athletes and 9 basketball players) participated in this study. After warm-up, subjects performed one maximum voluntary contraction (MVC) followed by fatigue test including sustained maximum isometric contraction of TS until the peak torque (PT) decreased to 50% of maximum value. Immediately after the test, subjects were asked to perform one MVC; then, root mean square (RMS), median frequency (MDF), median frequency slope (MDF slope), PT, falling slope (FSL) and the amount of pain were measured. RESULTS: In both groups shift of MDF slope to negative values, significant decrease of MDF and RMS occurred at the end of the fatigue test (P < 0.05). Immediately after the test, PT decreased significantly in both groups (P < 0.05), however, decrease of FSL was significant in non-athletes (P < 0.05) but not in athletes. After fatigue test, increase in Pain was significant in both groups (P < 0.05). Before fatigue test, at the end, and immediately after the test, MDF of non-athletes was more than athletes. There was no significant difference in RMS between the two groups. CONCLUSION: Our findings suggest that TS fatigue affects EMG parameters, PT and pain in athletes and non-athletes similarly.