Oxidative MnO2 Template Assisted Electrochemical Fabrication of Graphene/Polypyrrole Supercapacitor Electrodes.

Improving the morphological structure of active materials is a reliable strategy for the fabrication of high-performance supercapacitor electrodes. In this study, we introduce a feasible approach to constructing the graphene/polypyrrole (PPy) composite film implanted onto the current collector through a two-step electrochemical deposition method utilizing MnO2 as an intermediary template. The reduced graphene oxide (rGO) hydrogel film is first hydrothermally grown on a carbon cloth (CC) substrate to obtain a porous rGO@CC electrode on which MnO2 is electrodeposited. Then the as-prepared rGO/MnO2@CC electrode is subjected to the electrochemical polymerization of pyrrole, with MnO2 acting as an oxidizing template to facilitate the oxidative polymerization of pyrrole, ultimately yielding an rGO/PPy composite film on CC. The PPy synthesized via this methodology exhibits a distinctive interconnected structure, resulting in superior electrochemical performance compared with the electrode with PPy directly electrodeposited on rGO@CC. The optimized electrode achieves an impressive specific capacitance of 583.6 F g-1 at 1 A g-1 and retains 83% of its capacitance at 20 A g-1, with a capacitance loss of only 9.5% after 5000 charge-discharge cycles. The corresponding all-solid-state supercapacitor could provide a high energy density of 22.5 Wh kg-1 and a power density of 4.6 kW kg-1, with a capacitance retention of 82.7% after 5000 charge-discharge cycles. Furthermore, the device also demonstrates good flexibility performance upon bending at 90 and 180°. This work presents an innovative method for the preparation of carbon material/conducting polymer electrodes with specific structural characteristics and superior performance.

Causal roles of educational duration in bone mineral density and risk factors for osteoporosis: a Mendelian randomization study.

BACKGROUND: Educational duration might play a vital role in preventing the occurrence and development of osteoporosis(OP). PURPOSE: To assess the causal effect of educational duration on bone mineral density(BMD) and risk factors for OP by Mendelian randomization(MR) study. METHODS: The causal relationship was analyzed using data from genome-wide association study(GWAS). Inverse variance weighting (IVW) was used as the main analysis method. Horizontal pleiotropy was identified by MR-Egger intercept test, MR pleiotropy residual sum and outlier (MR-PRESSO) test. The leave-one-out method was used as a sensitivity analysis. RESULTS: The IVW results indicated that there was a positive causal relationship between educational duration and BMD (OR = 1.012, 95%CI:1.003-1.022), physical activity(PA) (OR = 1.156, 95%CI:1.032-1.295), calcium consumption (OR = 1.004, 95%CI:1.002-1.005), and coffee intake (OR = 1.019, 95%CI:1.014-1.024). There was a negative association between whole body fat mass (OR = 0.950, 95%CI:0.939-0.961), time for vigorous PA (OR = 0.955, 95%CI:0.939-0.972), sunbath (OR = 0.987, 95%CI:0.986-0.989), salt consumption (OR = 0.965, 95%CI:0.959-0.971), fizzy drink intake (OR = 0.985, 95%CI:0.978-0.992), smoking (OR = 0.969, 95%CI:0.964-0.975), and falling risk (OR = 0.976, 95%CI:0.965-0.987). There was no significant association between educational duration and lean mass, time for light-to-moderate PA, milk intake, and alcohol intake. Horizontal pleiotropy was absent in this study. The results were robust under sensitivity analyses. CONCLUSION: A longer educational duration was causally linked with increased BMD. No causal relationship had been found between educational duration and lean mass, time for light-to-moderate PA, milk intake, and alcohol consumption as risk factors for osteoporosis.

Causal roles of serum uric acid levels and gout in sepsis: a Mendelian randomization study.

OBJECTIVE: Several epidemiological studies have identified a potential link between serum uric acid(UA), gout and sepsis. The primary objective of this study is to delve deeper into this connection, investigating the causal effect of UA and gout on sepsis by applying Mendelian Randomization (MR). METHODS: The causal relationship was analyzed using data from genome-wide association study(GWAS). Inverse variance weighting (IVW) was used as the main analysis method. Three complementary methods were used for our MR analysis, which included the MR-Egger regression method, the weighted median method, the simple median method. Horizontal pleiotropy was identified by MR-Egger intercept test. Cochran's Q statistics were employed to assess the existence of instrument heterogeneity. The leave-one-out method was used as a sensitivity analysis. RESULTS: The IVW results indicated that there was a positive causal relationship between UA and sepsis(critical care) (OR = 0.24, 95%CI: 0.04 to 0.43, P = 0.018, F = 4291.20). There was no significant association between UA and sepsis(28 day death in critical care) (OR = 0.10, 95%CI: -0.29 to 0.50, P = 0.604). There was no significant association between gout and sepsis(critical care) (OR = 0.85, 95%CI: -4.87 to 6.57, P = 0.771), and sepsis(28 day death in critical care) (OR = -6.30, 95%CI: -17.41 to 4.81, P = 0.267). Horizontal pleiotropy was absent in this study. The results were robust under all sensitivity analyses. CONCLUSION: The study revealed that elevated UA levels was causally linked with sepsis(critical care). No causal relationship had been found between UA and sepsis(28 day death in critical care), as well as between gout and sepsis.

One-Step Fabrication of Integrated Graphene/Polypyrrole/Carbon Cloth Films for Supercapacitor Electrodes.

The facile and cost-effective preparation of supercapacitor electrodes is significant for the application of this kind of electrochemical energy-storing module. In this work, we designed a feasible strategy to fabricate a binary active material onto a current collector in one step. A colloidal mixture of graphene oxide and pyrrole layered on a carbon cloth could undergo a redox reaction through a mild hydrothermal process to yield a reduced graphene oxide/polypyrrole hydrogel film anchored onto the carbon cloth. The integrated electrode with the porous graphene/polypyrrole active material could be directly utilized as a freestanding working electrode for electrochemical measurements and the assembly of supercapacitor devices. The as-prepared electrode could achieve a high capacitance of 1221 mF cm-2 at 1 mA cm-2 (531 F g-1) with satisfactory cycling stability. The constructed symmetric supercapacitor with two optimal electrodes could provide an energy density of 70.4 µWh cm-2 (15.3 Wh kg-1). This work offers a feasible pathway toward the integration of graphene/conducting polymer composites as electrochemical electrodes.

Synthesis and biological evaluation of capsaicin analogues as antioxidant and neuroprotective agents.

Capsaicin and its analogues 3a-3q were designed and synthesized as potential new antioxidant and neuroprotective agents. Many analogues exhibited good antioxidant effects, and some showed more potent free radical scavenging activities than the positive drug quercetin (IC50 = 8.70 ± 1.75 µM for DPPH assay and 13.85 ± 2.87 µM for ABTS assay, respectively). The phenolic hydroxyl of capsaicin analogues was critical in determining antioxidant activity. Among these compounds, 3k displayed the most potent antioxidant activity. Cell vitality tests revealed that the representative compound 3k was good at protecting cells from H2O2-induced oxidative damage at low concentrations (cell viability increased to 90.0 ± 5.5% at 10 µM). In addition, the study demonstrated that 3k could reduce intracellular ROS accumulation and increase GSH levels to prevent H2O2-induced oxidative stress in SY5Y cells. In the mitochondrial membrane potential assay, 3k significantly increased the MMP level of SY5Y cells treated with H2O2 and played an anti-neuronal cell death role. These results provide a promising strategy to develop novel capsaicin analogues as potential antioxidant and neuroprotective agents.

Mesoporous TiO2 layer suppresses ion accumulation in perovskite solar cells.

Ion accumulation in perovskite solar cells can be highly suppressed by a mesoporous TiO2 layer. This is evidenced by the decrease of the ion-related electrostatic potential with increasing the thickness of the mesoporous layer, accounted for by the electron population in the shallow trap states of the TiO2 nanocrystals.

Does prior exposure to immune checkpoint inhibitors treatment affect incidence and mortality of COVID-19 among the cancer patients: The systematic review and meta-analysis.

BACKGROUND: Immune checkpoint inhibitors (ICIs) treatment among cancer patients has been shown to have antiviral effects by reactivating exhausted T cells. However, they could also trigger inflammatory storm. Therefore, prior exposure to ICIs may influence the risk of SARS-CoV2 infection and subsequent mortality. Recent results from studies of ICIs treatment on incidence and mortality of COVID-19 are controversial. MATERIALS AND METHODS: We searched databases PubMed, Embase, ISI of Knowledge, Cochrane Central Register of Controlled Trials (CENTRAL), as well as pre-print databases (MedRxiv and BioRxiv) for retrospective and prospective studies comparing ICIs versus other antitumor treatments in cancer patients in the area of COVID-19 pandemic. The primary outcome was the incidence of COVID-19. The secondary outcomes were mortality of COVID-19. RESULTS: Twenty-three studies with a total of 117,735 patients were selected. Compared with other antitumor treatments, prior exposure to ICIs had not an increased risk of incidence [Odds ratio (OR), 0.84; 95% confidence interval (CI), 0.60-1.18; P = 0.32] and mortality (OR, 1.22; 95% CI, 0.91-1.62; P = 0.18) of COVID-19 infectioin. Our subgroup and meta-regression analyses indicated that prior exposure to ICIs may reduce the incidence of COVID-19 in metastatic cancer patients. CONCLUSIONS: There was no significant difference on incidence and mortality of COVID-19 between prior exposure to ICIs with other anti-tumor treatments. ICIs may reduce infection susceptibility of COVID-19 in metastatic cancer patients.

Influence of the MACl additive on grain boundaries, trap-state properties, and charge dynamics in perovskite solar cells.

Grain boundary trap passivation in perovskite films has become one of the most effective strategies for suppressing the charge recombination and enhancing the photovoltaic performance of perovskite solar cells, whereas the relevant trap-state properties and the charge carrier dynamics need to be further clarified. In this work, the CH3NH3Cl (MACl) additive is introduced into the MAI:PbI2 precursor solution to obtain perovskite films comprising various grain sizes with distinct grain boundaries and trap-state properties. The influence of grain boundary traps passivated with the MACl additive on trap-state properties and charge carrier transport/recombination dynamics is systematically studied with time-resolved spectroscopic and transient photoelectric characterization. Specifically, the MACl amount determines the content of the PbI2 residual in the final perovskite, leading to photoluminescence quenching induced by charge transfer. The trap-state distribution result reveals that the deep-level traps at the grain boundaries as the main sources of charge recombination centers are dramatically passivated. Low-temperature photoluminescence spectroscopy distinguishes and compares the trap-state emission related to different perovskite phases. Transient photoelectric measurements including photovoltage decay and charge extraction further demonstrate that the boundary trap passivation can effectively promote charge transport and inhibit charge recombination in devices treated with the optimized MACl amount. As a result, the corresponding device possesses superior photovoltaic parameters to the control device. This work proposes a systematic understanding of the grain boundary trap passivation strategy and provides a new insight into the development of high-performance perovskite solar cells.

[Analysis of related factors of carbapenem resistant Klebsiella pneumoniae infection in patients with artificial airway].

OBJECTIVE: To analyze the clinical characteristics and related influencing factors of carbapenem resistant Klebsiella pneumoniae (CRKP) in patients with artificial airway and mechanical ventilation in intensive care unit (ICU), and provide theoretical basis for clinical prevention of Klebsiella pneumoniae infection. METHODS: The clinical data of patients with pulmonary infection of Klebsiella pneumoniae in ICU of Beijing Shijitan Hospital Affiliated to Capital Medical University from January 2016 to December 2019 were collected. Compared CRKP pneumonia patients (study group) with carbapenem antibiotic sensitive Klebsiella pneumoniae (CSKP) pneumonia patients (control group), the clinical characteristics [gender, age, acute physiology and chronic health evaluation II (APACHE II), duration of mechanical ventilation, proportion of patients with mechanical ventilation > 10 days, use of antibiotics before detection of Klebsiella pneumoniae, white blood cell count (WBC), C-reactive protein (CRP), procalcitonin (PCT), albumin, bedridden for more than 1 month before admission, 28-day mortality] were analyzed. The drug resistance rates of Klebsiella pneumoniae in both groups and difference of drug resistance rate of Klebsiella pneumoniae to different antibiotics from 2016 to 2019 were compared. The risk factors of CRKP infection were analyzed by multivariate Logistic regression, and the related drug resistance genes were detected. RESULTS: Compared with the control group, the study group was older [years old: 81.5 (72.0, 86.0) vs. 78.0 (71.0, 80.5)], APACHE II [point: 25.00 (20.00, 34.00) vs. 19.00 (14.00, 23.25)] and proportion of patients with mechanical ventilation > 10 days [63.2% (182/288) vs. 12.8% (10/78)], the use of ß-lactamase inhibitor antibiotics before detection of Klebsiella pneumoniae [75.69% (218/288) vs. 30.77% (24/78)], the use of carbapenems [79.86% (230/288) vs. 41.03% (32/78)], the use of more than two kinds of antibiotics [80.90% (233/288) vs. 29.49% (23/78)], proportion of patients staying in bed for more than 1 month before admission [40.97% (118/288) vs. 11.54% (9/78)] and WBC [×109/L: 9.72 (6.41, 14.69) vs. 7.57 (5.84, 12.61)], CRP [mg/L: 74.45 (36.30, 158.88) vs. 39.22 (13.68, 92.51)], PCT [µg/L: 3.87 (0.82, 19.24) vs. 0.51 (0.25, 5.71)], 28-day mortality [21.5% (62/288) vs. 10.3% (8/78)] were higher, albumin [g/L: 24.1 (18.3, 28.6) vs. 30.1 (23.8, 35.1)] was lower, duration of mechanical ventilation [days: 16.5 (9.0, 19.0) vs. 7.0 (5.0, 10.0)] was longer, the proportion of patients with chronic obstructive pulmonary disease [COPD: 35.76% (103/288) vs. 11.54% (9/78)], malignant tumor [18.06% (52/288) vs. 5.13% (4/78)], renal failure [31.94% (92/288) vs. 11.54% (9/78)], shock [51.74% (149/288) vs. 19.23% (15/78)] were higher, and the differences were statistically significant (all P < 0.05). The drug resistance rates of Klebsiella pneumoniae to aztreonam, piperacillin/tazobactam, imipenem and ciprofloxacin were statistically significant (all P < 0.05); the drug resistance rates of Klebsiella pneumoniae to aztreonam and piperacillin/tazobactam were the highest in 2019 (88.17% and 86.02%, respectively), and the lowest in 2016 (70.65% and 57.61%, respectively). The drug resistance rate to imipenem was the highest in 2018 (86.32%), the lowest in 2016 (59.78%); the resistance rate to ciprofloxacin was the highest in 2016 (76.09%), and the lowest in 2018 (53.68%). The resistance rates of ceftetan, amikacin, piperacillin/tazobactam, ceftazidime, ceftriaxone and gentamicin in the study group were significantly higher than those in the control group (82.99% vs. 62.82%, 49.31% vs. 17.95%, 75.69% vs. 60.26%, 81.25% vs. 64.10%, 80.21% vs. 58.97%, 91.32% vs. 60.26%, all P < 0.05). Logistic regression analysis showed that COPD, severe hypoproteinemia, mechanical ventilation time > 10 days and the use of carbapenem antibiotics before detection of Klebsiella pneumoniae were independent risk factors of CRKP infection. Gene detection showed that there were TEM, KPC, AmpC, AAC(3)-II, ant(3")-I, qnrS and other drug resistance genes in CRKP. The detection rate of TEM was the highest (74.00%), and qnrA was the lowest (6.67%). CONCLUSIONS: The occurrence of CRKP in ICU patients with artificial airway and mechanical ventilation is related to many factors. It is necessary to shorten the mechanical ventilation time, avoid the nonstandard use of carbapenem antibiotics, and improve the serum albumin level, so as to reduce the incidence of CRKP pneumonia and improve the prognosis of patients.

The influence of the electron transport layer on charge dynamics and trap-state properties in planar perovskite solar cells.

Despite the outstanding photovoltaic performance of perovskite solar cells, the correlation between the electron transport layer and the mechanism of photoelectric conversion is still not fully understood. In this paper, the relationship between photovoltaic performance and carrier dynamics is systematically studied in both TiO2- and SnO2-based planar perovskite devices. It is found that the different electron transport layers result in distinct forward scan results and charge dynamics. Based on the charge dynamics results, the influence of the electron transport layer on charge carrier transport and charge recombination is revealed. More importantly, the trap-state density is characterized, which is proven to be related to the charge carrier dynamics and the specific hysteresis behaviour in the perovskite solar cells. The present work would provide new insights into the working mechanisms of electron transport layers and their effect on hysteresis.

Modification of NiO x hole transport layer for acceleration of charge extraction in inverted perovskite solar cells.

The modification of the inorganic hole transport layer has been an efficient method for optimizing the performance of inverted perovskite solar cells. In this work, we propose a facile modification of a compact NiO x film with NiO x nanoparticles and explore the effects on the charge carrier dynamic behaviors and photovoltaic performance of inverted perovskite devices. The modification of the NiO x hole transport layer can not only enlarge the surface area and infiltration ability, but also adjust the valence band maximum to well match that of perovskite. The photoluminescence results confirm the acceleration of the charge separation and transport at the NiO x /perovskite interface. The corresponding device possesses better photovoltaic parameters than the device based on control NiO x films. Moreover, the charge carrier transport/recombination dynamics are further systematically investigated by the measurements of time-resolved photoluminescence, transient photovoltage and transient photocurrent. Consequently, the results demonstrate that proper modification of NiO x can significantly enlarge interface area and improve the hole extraction capacity, thus efficiently promoting charge separation and inhibiting charge recombination, which leads to the enhancement of the device performances.

Charge carrier recombination dynamics in a bi-cationic perovskite solar cell.

The compositional engineering is of great importance to tune the electrical and optical properties of perovskite and improve the photovoltaic performance of perovskite solar cells. The exploration of the corresponding photoelectric conversion processes, especially the carrier recombination dynamics, will contribute to the optimization of the devices. In this work, perovskite with mixed methylammonium (MA) and formamidinium (FA) as organic cations, MA0.4FA0.6PbI3, is fabricated to study the influence of the bi-cation on the charge carrier recombination dynamics. X-ray diffraction analysis indicates the existence of the MAPbI3-FAPbI3 phase segregation in the bi-cationic perovskite crystal. The time-resolved photoluminescence dynamics presents a relatively fast carrier recombination process ascribed to the charge transfer from MAPbI3 to FAPbI3 in the bi-cationic perovskite film. The carrier recombination dynamics investigated by transient photovoltage measurements reveals a biphasic trap-assisted carrier recombination mechanism in the bi-cationic device, which involves carrier recombination in the MAPbI3 phase and FAPbI3 phase, respectively. The ultimate presentation of the carrier recombination process is closely related to the charge transfer between the two perovskite phases.

Identification of novel uracil derivatives incorporating benzoic acid moieties as highly potent Dipeptidyl Peptidase-IV inhibitors.

Dipeptidyl Peptidase-IV (DPP-4) is a validated therapeutic target for type 2 diabetes. Aiming to interact with both residues Try629 and Lys554 in S2' site, a series of novel uracil derivatives 1a-l and 2a-i incorporating benzoic acid moieties at the N3 position were designed and evaluated for their DPP-4 inhibitory activity. Structure-activity relationships (SAR) study led to the identification of the optimal compound 2b as a potent and selective DPP-4 inhibitor (IC50 = 1.7 nM). Docking study revealed the additional salt bridge formed between the carboxylic acid and primary amine of Lys554 has a key role in the enhancement of the activity. Furthermore, compound 2b exhibited no cytotoxicity in human hepatocyte LO2 cells up to 50 µM. Subsequent in vivo evaluations revealed that the ester of 2b robustly improves the glucose tolerance in normal mice. The overall results have shown that compound 2b has the potential to a safe and efficacious treatment for T2DM.

Preparation of graphene/Au aerogel film through the hydrothermal process and application for H2O2 detection.

In this paper, one-step preparation of graphene/gold nanoparticle hydrogel film through the hydrothermal method is reported. The hydrogel film could be formed on a glass substrate under hydrothermal conditions, and upon freeze-drying, the aerogel film of 40 µm thickness with satisfying flexibility and strength is obtained. The aerogel composite film is characterized by scanning/transmission electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. Moreover, the aerogel film is directly used as the electrochemical electrode for sensing H2O2, and exhibits good performance with a broad linear range, low detection limit and excellent selectivity. This work provides a route for the fabrication of graphene film material with wide potential in various aspects.

Synthesis, crystal structure and photophysical properties of 1,4-bis(1,3-diazaazulen-2-yl)benzene: a new π building block.

A dimerized 1,3-diazaazulene derivative, namely 1,4-bis(1,3-diazaazulen-2-yl)benzene [or 2,2'-(1,4-phenylene)bis(1,3-diazaazulene)], C22H14N4, (I), has been synthesized successfully through the condensation reaction between 2-methoxytropone and benzene-1,4-dicarboximidamide hydrochloride, and was characterized by 1H NMR and 13C NMR spectroscopies, and ESI-MS. X-ray diffraction analysis reveals that (I) has a nearly planar structure with good π-electron delocalization, indicating that it might serve as a π building block. The crystal belongs to the monoclinic system. One-dimensional chains were formed along the a axis through π-π interactions and adjacent chains are stabilized by C-H...N interactions, forming a three-dimensional architecture. The solid emission of (I) in the crystalline form exhibited a 170 nm red shift compared with that in the solution state. The observed optical bandgap for (I) is 3.22 eV and a cyclic voltammetry experiment confirmed the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The calculated bandgap for (I) is 3.37 eV, which is very close to the experimental result. In addition, the polarizability and hyperpolarizability of (I) were appraised for its further application in second-order nonlinear optical materials.

Characterization of the influences of morphology on the intrinsic properties of perovskite films by temperature-dependent and time-resolved spectroscopies.

Organic-inorganic halide perovskites have attracted enormous attention owing to their promising application in photovoltaic devices. The morphology of the perovskites is the key to driving the performance of perovskite devices, which necessitates a systematic study. In this work, two typical morphologies, i.e., flake and cube, of perovskite films are fabricated, and the temperature-dependent optical absorption and photoluminescence properties of the two types of perovskite film are systematically investigated. From the temperature-dependent spectra, both exciton and phase transition temperatures of the flake film are found to be about 10 K lower than those of the cube one. Meanwhile, the influences of the morphology on the exciton binding energy, optical phonon energy and polaron binding energy are quantitatively characterized. The exciton binding of the flake film is nearly three times smaller than that of the cube one, while the phonon coupling energy and the polaron binding energy of the former are about 5 meV and 2 meV larger than those of the latter. Furthermore, the results of photoluminescence lifetime and charge separation efficiency further reveal that the charge carrier kinetics in the two kinds of perovskite films is significantly different. The current study provides a theoretical framework to understand the fundamental physics of perovskites and to promote the design and enhancement of active materials for improved optoelectronic devices.

Dual antiplatelet therapy after coronary artery bypass surgery: is there an increase in bleeding risk? A meta-analysis.

OBJECTIVES: There is increasing evidence that dual antiplatelet therapy (DAPT) when compared with single antiplatelet therapy may improve venous graft patency after coronary artery bypass graft. However, it is not yet known whether postoperative administration of DAPT may increase the potential risk of bleeding, especially in the early postoperative period. METHODS: We searched studies on PubMed, Embase, Web of Science and the Cochrane Central Register of Controlled Trials. Relative risk (RR) was pooled with 95% confidence intervals (CIs) for dichotomous data. Prior subgroup analyses were performed to look for potential heterogeneity. RESULTS: Thirteen studies involving 23 591 participants were included. Our meta-analysis showed that DAPT does not increase the risk of major bleeding (randomized controlled trials group: RR = 1.28, 95% CI 0.95-1.71; cohort studies group: RR = 0.99, 95% CI 0.66-1.51) and minor bleeding (randomized controlled trials group: RR = 1.15, 95% CI 0.73-1.81; cohort studies group: RR = 0.84, 95% CI 0.37-1.93) when compared with single antiplatelet therapy. Meanwhile, DAPT does not increase the incidence of major bleeding events during hospitalization (randomized controlled trials group: RR = 1.27, 95% CI 0.91-1.78; cohort studies group: RR = 0.50, 95% CI 0.12-2.09). Sensitivity analyses showed that our results are stable, and there was no evidence of publication bias. CONCLUSIONS: DAPT does not increase the risk of major bleeding and minor bleeding when compared with single antiplatelet therapy. Postoperative administration of DAPT is considered to be safe in patients after coronary artery bypass graft, even in the early postoperative period.

Multiple-Trapping Model for the Charge Recombination Dynamics in Mesoporous-Structured Perovskite Solar Cells.

The photovoltaic performance of organic-inorganic hybrid perovskite solar cells has reached a bottleneck after rapid development in last few years. Further breakthrough in this field requires deeper understanding of the underlying mechanism of the photoelectric conversion process in the device, especially the dynamics of charge-carrier recombination. Originating from dye-sensitized solar cells (DSSCs), mesoporous-structured perovskite solar cells (MPSCs) have shown many similarities to DSSCs with respect to their photoelectric dynamics. Herein, by applying the multiple-trapping model of the charge-recombination dynamic process for DSSCs in MPSCs, with rational modification, a novel physical model is proposed to describe the dynamics of charge recombination in MPSCs that exhibits good agreement with experimental data. Accordingly, the perovskite- and TiO2 -dominating charge-recombination processes are assigned and their relationships with the trap-state distribution are also discussed. An optimal balance between these two dynamic processes is required to improve the performance of mesoporous-structured perovskite devices.

Power output and carrier dynamics studies of perovskite solar cells under working conditions.

Perovskite solar cells have emerged as promising photovoltaic systems with superb power conversion efficiency. For the practical application of perovskite devices, the greatest concerns are the power output density and the related dynamics under working conditions. In this study, the working conditions of planar and mesoscopic perovskite solar cells are simulated and the power output density evolutions with the working voltage are highlighted. The planar device exhibits higher capability of outputting power than the mesoscopic one. The transient photoelectric conversion dynamics are investigated under the open circuit, short circuit and working conditions. It is found that the power output and dynamic processes are correlated intrinsically, which suggests that the power output is the competitive result of the charge carrier recombination and transport. The present work offers a unique view to elucidating the relationship between the power output and the charge carrier dynamics for perovskite solar cells in a comprehensive manner, which would be beneficial to their future practical applications.

Adverse Effects of Excess Residual PbI2 on Photovoltaic Performance, Charge Separation, and Trap-State Properties in Mesoporous Structured Perovskite Solar Cells.

Organic-inorganic halide perovskite solar cells have rapidly come to prominence in the photovoltaic field. In this context, CH3 NH3 PbI3 , as the most widely adopted active layer, has been attracting great attention. Generally, in a CH3 NH3 PbI3 layer, unreacted PbI2 inevitably coexists with the perovskite crystals, especially following a two-step fabrication process. There appears to be a consensus that an appropriate amount of unreacted PbI2 is beneficial to the overall photovoltaic performance of a device, the only disadvantageous aspect of excess residual PbI2 being viewed as its insulating nature. However, the further development of such perovskite-based devices requires a deeper understanding of the role of residual PbI2 . In this work, PbI2 -enriched and PbI2 -controlled perovskite films, as two extreme cases, have been prepared by modulating the crystallinity of a pre-deposited PbI2 film. The effects of excess residual PbI2 have been elucidated on the basis of spectroscopic and optoelectronic studies. The initial charge separation, the trap-state density, and the trap-state distribution have all been found to be adversely affected in PbI2 -enriched devices, to the detriment of photovoltaic performance. This leads to a biphasic recombination process and accelerates the charge carrier recombination dynamics.