Photoexcited Carrier Dynamics in Iodine-Doped CH3NH3PbBr3 Single Crystals.

Iodine-doped bromide perovskite single crystals (IBPSCs) have important applications in optoelectronic fields, such as in solar cells. Currently, much research has aimed to study the phase separation phenomenon and device performance improvements in IBPSCs. However, important intrinsic photoexcited carrier dynamics are often overlooked in IBPSCs. Here, we explored the photoexcited carrier dynamics in typical iodine-doped MAPbBr3 single crystals using the excitation intensity-dependent steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) technique. We found that the trap state density changes with an increase in the amount of doped iodine. Further, we noticed that there is an influence of carrier diffusion on the photoexcited carrier dynamics, and then, we evaluated the carrier diffusion coefficients and recombination constants via numerical simulations of the PL kinetics. Consequently, we found that the electron shallow trap-related carrier behaviors substantially impacted the PL kinetics. Our results greatly facilitate a deeper understanding of the fundamental characteristics of mixed halide perovskite material.

Stronger Coupling of Quantum Dots in Hole Transport Layer Through Intermediate Ligand Exchange to Enhance the Efficiency of PbS Quantum Dot Solar Cells.

Nowadays, the extensively used lead sulfide (PbS) quantum dot (QD) hole transport layer (HTL) relies on layer-by-layer method to replace long chain oleic acid (OA) ligands with short 1,2-ethanedithiol (EDT) ligands for preparation. However, the inevitable significant volume shrinkage caused by this traditional method will result in undesired cracks and disordered QD arrangement in the film, along with adverse increased defect density and inhomogeneous energy landscape. To solve the problem, a novel method for EDT passivated PbS QD (PbS-EDT) HTL preparation using small-sized benzoic acid (BA) as intermediate ligands is proposed in this work. BA is substituted for OA ligands in solution followed by ligand exchange with EDT layer by layer. With the new method, smoother PbS-EDT films with more ordered and closer QD packing are gained. It is demonstrated stronger coupling between QDs and reduced defects in the QD HTL owing to the intermediate BA ligand exchange. As a result, the suppressed nonradiative recombination and enhanced carrier mobility are achieved, contributing to ≈20% growth in short circuit current density (Jsc) and a 23.4% higher power conversion efficiency (PCE) of 13.2%. This work provides a general framework for layer-by-layer QD film manufacturing optimization.

In situ synergistic halogen passivation of semiconducting PbS quantum dot inks for efficient photovoltaics.

Lead sulfide colloidal quantum dots (PbS CQDs) show great potential in next-generation photovoltaics. However, their high specific surface area and complex surface crystallography lead to a high surface trap density, which normally requires more than one type of capping ion or ligand to achieve effective surface passivation. In this study, we performed in situ mixed halogen passivation (MHP) during the direct synthesis of semiconducting PbS CQD inks by using different lead halogens. The different halogens can bind with the surface of the CQD throughout the nucleation/growth process, resulting in optimal surface configuration. As a result, the MHP CQD exhibited superior surface passivation compared to the conventionally iodine-capped CQDs. Finally, we achieved a substantial improvement in efficiency from 10.64% to 12.58% after the MHP treatment. Our work demonstrates the advantages of exploring efficient passivation in the directly synthesized CQD inks.

Stable Inorganic Colloidal Tin and Tin-Lead Perovskite Nanocrystals with Ultralong Carrier Lifetime via Sn(IV) Control.

Inorganic tin (Sn) perovskite nanocrystals offer a promising solution to the potential toxicity concerns associated with their established lead (Pb)-based counterparts. Yet, achieving their superior stability and optoelectronic properties remains an ongoing challenge. Here, we report a synthesis of high-symmetry α-phase CsSnI3 nanocrystals with an ultralong 278 ns carrier lifetime, exceeding previous benchmarks by 2 orders of magnitude through meticulous Sn(IV) control. The nanocrystals demonstrate excellent colloidal stability, uniform monodispersity, and a distinct exciton peak. Central to these outcomes is our designed solid-liquid antioxidation suspension of tri-n-octylphosphine (TOP) and zerovalent tin (Sn(0)) that fully addresses the unique coexisting oxygen-driven and solvent-driven Sn oxidation mechanisms in Sn perovskite nanocrystal synthesis. We uncover the largely undervalued function of TOP in mitigating oxygen-driven Sn oxidation and introduce Sn(0) powder to generate a synergistic antioxidation function with TOP, significantly reducing Sn(IV)-induced defects and distortions and contributing to enhanced optoelectronic properties. Strikingly, this approach also profoundly impacts inorganic Sn-Pb perovskite nanocrystals, boosting lifetimes by 2 orders of magnitude and increasing photoluminescence quantum yield over 100-fold to 35%. Our findings illuminate the potential of Sn-based nanocrystals for optoelectronic applications.

Open-Shell Diradical-Sensitized Electron Transport Layer for High-Performance Colloidal Quantum Dot Solar Cells.

The zinc oxide (ZnO) nanoparticles (NPs) are well-documented as an excellent electron transport layer (ETL) in optoelectronic devices. However, the intrinsic surface flaw of the ZnO NPs can easily result in serious surface recombination of carriers. Exploring effective passivation methods of ZnO NPs is essential to maximize the device's performance. Herein, a hybrid strategy is explored for the first time to improve the quality of ZnO ETL by incorporating stable organic open-shell donor-acceptor type diradicaloids. The high electron-donating feature of the diradical molecules can efficiently passivate the deep-level trap states and improve the conductivity of ZnO NP film. The unique advantage of the radical strategy is that its passivation effectiveness is highly correlated with the electron-donating ability of radical molecules, which can be precisely controlled by the rational design of molecular chemical structures. The well-passivated ZnO ETL is applied in lead sulfide (PbS) colloidal quantum dot solar cells, delivering a power conversion efficiency of 13.54%. More importantly, as a proof-of-concept study, this work will inspire the exploration of general strategies using radical molecules to construct high-efficiency solution-processed optoelectronic devices.

Breaking the Size Limitation of Directly-Synthesized PbS Quantum Dot Inks Toward Efficient Short-wavelength Infrared Optoelectronic Applications.

PbS quantum dots (QDs) are promising building blocks for solution-processed short-wavelength infrared (SWIR) devices. The recently developed direct synthesis of semi-conductive PbS QD inks has substantially simplified the preparation processing and reduced the material cost, while facing the challenge to synthesize large-size QDs with absorption covering the SWIR region. Herein, we for the first time realize a low-cost, scalable synthesis of SWIR PbS QD inks after an extensive investigation of the reaction kinetics. Finally, based on these PbS SWIR QD inks, the solar cell demonstrates a record-high power conversion efficiency (PCE) of 1.44 % through an 1100 nm cutoff silicon filter and the photodetector device shows a low dark current density of 2×10-6  A cm-2 at -0.8 V reverse bias with a high external quantum efficiency (EQE) of 70 % at ≈1300 nm. Our results realize the direct synthesis of low-cost and scalable SWIR QD inks and may accelerate the industrialization of consumer SWIR technologies.

Merging Passivation in Synthesis Enabling the Lowest Open-Circuit Voltage Loss for PbS Quantum Dot Solar Cells.

The high open-circuit voltage (Voc ) loss arising from insufficient surface passivation is the main factor that limits the efficiency of current lead sulfide colloidal quantum dots (PbS CQDs) solar cell. Here, synergistic passivation is performed in the direct synthesis of conductive PbS CQD inks by introducing multifunctional ligands to well coordinate the complicated CQDs surface with the thermodynamically optimal configuration. The improved passivation effect is intactly delivered to the final photovoltaic device, leading to an order lower surface trap density and beneficial doping behavior compared to the control sample. The obtained CQD inks show the highest photoluminescence quantum yield (PLQY) of 24% for all photovoltaic PbS CQD inks, which is more than twice the reported average PLQY value of ≈10%. As a result, a high Voc of 0.71 V and power conversion efficiency (PCE) of 13.3% is achieved, which results in the lowest Voc loss (0.35 eV) for the reported PbS CQD solar cells with PCE >10%, comparable to that of perovskite solar cells. This work provides valuable insights into the future CQDs passivation strategies and also demonstrates the great potential for the direct-synthesis protocol of PbS CQDs.

Homologous Bromides Treatment for Improving the Open-Circuit Voltage of Perovskite Solar Cells.

The power conversion efficiency (PCE) of solution-processed organic-inorganic mixed halide perovskite solar cells has achieved rapid improvement. However, it is imperative to minimize the voltage deficit (Woc  = Eg /q - Voc ) for their PCE to approach the theoretical limit. Herein, the strategy of depositing homologous bromide salts on the perovskite surface to achieve a surface and bulk passivation for the fabrication of solar cells with high open-circuit voltage is reported. Distinct from the conclusions given by previous works, that homologous bromides such as FABr only react with PbI2 to form a large-bandgap perovskite layer on top of the original perovskite, this work shows that the bromide also penetrates the perovskite film and passivates the perovskite in the bulk. This is confirmed by the small-bandgap enlargement observed by absorbance and photoluminescence, and the bromide element ratio increasing in the bulk by time-of-flight secondary-ion mass spectrometry and depth-resolved X-ray photoelectron spectroscopy. Furthermore, a clear suppression of non-radiative recombination is confirmed by a variety of characterization methods. This work provides a simple and universal way to reduce the Woc of single-junction perovskite solar cells and it will also shed light on developing other high-performance optoelectronic devices, including perovskite-based tandems and light-emitting diodes.

The effect of water on colloidal quantum dot solar cells.

Almost all surfaces sensitive to the ambient environment are covered by water, whereas the impacts of water on surface-dominated colloidal quantum dot (CQD) semiconductor electronics have rarely been explored. Here, strongly hydrogen-bonded water on hydroxylated lead sulfide (PbS) CQD is identified. The water could pilot the thermally induced evolution of surface chemical environment, which significantly influences the nanostructures, carrier dynamics, and trap behaviors in CQD solar cells. The aggravation of surface hydroxylation and water adsorption triggers epitaxial CQD fusion during device fabrication under humid ambient, giving rise to the inter-band traps and deficiency in solar cells. To address this problem, meniscus-guided-coating technique is introduced to achieve dense-packed CQD solids and extrude ambient water, improving device performance and thermal stability. Our works not only elucidate the water involved PbS CQD surface chemistry, but may also achieve a comprehensive understanding of the impact of ambient water on CQD based electronics.

Toward printable solar cells based on PbX colloidal quantum dot inks.

Lead chalcogenide (PbX, X = S, Se) colloidal quantum dots (CQDs) are promising solution-processed semiconductor materials for the construction of low-cost, large-area, and flexible solar cells. The properties of CQDs endow them with advantages in semi-conducting film deposition compared to other solution-processed photovoltaic materials, which is critical for the fabrication of efficient large-area solar cells towards industrialization. However, the development of large-area CQD solar cells is impeded by the conventional solid-state ligand exchange process, where the tedious processing with high expense is indispensable to facilitate charge transport of CQD films for photovoltaic applications. In the past several years, the rapid development of CQD inks has boosted the device performance and dramatically simplified the fabrication process. The CQD inks are compatible with most of the industrialized printing techniques, demonstrating potential in fabricating solar modules for commercialization. This article aims to review the recent advances in solar cells based on PbX CQD inks, including both lab-scale and large-area photovoltaic devices prepared from solution-phase ligand exchange (SPLE) as well as the recently invented "one-step" synthesis. We expect to draw attention to the enormous potential of CQD inks for developing high-efficiency and low-cost large-area photovoltaics.

Interfacial Energy Level Tuning for Efficient and Thermostable CsPbI2Br Perovskite Solar Cells.

Inorganic mixed-halide CsPbX3-based perovskite solar cells (PeSCs) are emerging as one of the most promising types of PeSCs on account of their thermostability compared to organic-inorganic hybrid counterparts. However, dissatisfactory device performance and high processing temperature impede their development for viable applications. Herein, a facile route is presented for tuning the energy levels and electrical properties of sol-gel-derived ZnO electron transport material (ETM) via the doping of a classical alkali metal carbonate Cs2CO3. Compared to bare ZnO, Cs2CO3-doped ZnO possesses more favorable interface energetics in contact with the CsPbI2Br perovskite layer, which can reduce the ohmic loss to a negligible level. The optimized PeSCs achieve an improved open-circuit voltage of 1.28 V, together with an increase in fill factor and short-circuit current. The optimized power conversion efficiencies of 16.42% and 14.82% are realized on rigid glass substrate and flexible plastic substrate, respectively. A high thermostability can be simultaneously obtained via defect passivation at the Cs2CO3-doped ZnO/CsPbI2Br interface, and 81% of the initial efficiency is retained after aging for 200 h at 85 °C.

Complete chloroplast genome of Senna spectabilis (DC.) H.S. Irwin & Barneby (Fabaceae) and phylogenetic analysis.

Senna spectabilis (DC.) H.S. Irwin & Barneby is a popular ornamental tree as well as a traditional medical plant in Cameroon. In this study, we sequenced and annotated the complete chloroplast genome of S. spectabilis and reconstructed the phylogenetic relationship of the tribe Cassieae. The length of the chloroplast genome was determined to be 162,754 bp, containing a pair of inverted repeats of 25,413 bp which separated by a small single-copy (SSC) region of 20,161 bp and a large single-copy (LSC) region of 91,767 bp. The cp genome encodes 128 genes, including 83 protein-coding genes, 37 tRNA genes, and eight rRNA genes. The percentage of total GC content of this genome was 35.7%. The phylogenetic analysis indicates that S. spectabilis with the sampled Senna species formed a well-supported monophyletic clade.

Complete plastome sequence of Jacaranda mimosifolia D. Don (Bignoniaceae): a beautiful landscaping tree species.

Jacaranda mimosifolia is a deciduous arbor with blue flowers native to Brazil, Bolivia, and Argentina in South America. After introduction from South America, it was widely cultivated as a garden ornamental plant in South China. The complete chloroplast (cp) genome sequence of this ornamental species is reported in this study, based on high-throughput sequencing (Illumina). The complete cp genome is 153,514 bp in length, containing a pair of inverted repeat regions (IRs) of 25,408 bp, a large single-copy (LSC) region of 84,755 bp, and a small single-copy (SSC) region of 17,943 bp. The cp genome contains 130 genes, consisting of 85 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. The overall A/T content in the cp genome of J. mimosifolia is 61.70%. The phylogenetic analyses indicate that there is a close relationship between J. mimosifolia and Tecomaria capensis. The complete cp sequence of J. mimosifolia will provide a useful resource for the development and utilization of this species as well as for the phylogenetic studies in Bignoniaceae.

Complete plastome sequence of Elaeagnus glabra (Elaeagnaceae): an Asian endemic plant species.

Elaeagnus glabra is an evergreen vine or climbing shrub with 5 m height. It is widespread in southern China. It grows in the sunny forests or forest margins below 1000 m a.s.l. In this paper, we report and describe the complete plastome of E. glabra in order to provide useful genomic data for its systematic research. The complete plastome of E. glabra is 152,555 bp with a typical quadripartite structure of angiosperms. It contains two Inverted Repeats (IRs) of 25,918 bp, a large single-copy (LSC) of 82,408 bp, and a small single-copy (SSC) region of 18,311 bp. The complete plastome contains 129 genes, including 83 protein-coding genes, 38 tRNA genes, and eight rRNA genes. The overall A/T content in the chloroplast genome of E. glabra is 62.90%. The phylogenetic analysis indicated that E. glabra is close to E. loureirii within Elaeagnaceae. The complete plastome of E. glabra will provide useful resources for the development and utilization of this species and the phylogenetic study of Rosales.

High-Efficiency PbS Quantum-Dot Solar Cells with Greatly Simplified Fabrication Processing via "Solvent-Curing".

PbS quantum-dot (QD) solar cells are promising candidates for low-cost solution-processed photovoltaics. However, the device fabrication usually requires ten more times film deposition and rinsing steps, which is not ideal for scalable manufacturing. Here, a greatly simplified deposition processing is demonstrated by replacing methanol with acetonitrile (ACN) as the rinsing solvent. It is discovered that ACN can effectively "cure" the film cracks generated from the volume loss during the solid-state ligand-exchange process, which enables the deposition of thick and dense films with much fewer deposition steps. Meanwhile, due to the aprotic nature of ACN, fewer trap states can be introduced during the rinsing process. As a result, with only three deposition steps for the active layer, a CPVT-certified 11.21% power conversion efficiency is obtained, which is the highest efficiency ever reported for PbS QD solar cells employing a solid-state ligand-exchange process. More importantly, the simple film-deposition processing provides an opportunity for the future application of QDs in low-cost printing of optoelectronic devices.

In Situ Passivation for Efficient PbS Quantum Dot Solar Cells by Precursor Engineering.

Current efforts on lead sulfide quantum dot (PbS QD) solar cells are mostly paid to the device architecture engineering and postsynthetic surface modification, while very rare work regarding the optimization of PbS synthesis is reported. Here, PbS QDs are successfully synthesized using PbO and PbAc2  ·â€†3H2 O as the lead sources. QD solar cells based on PbAc-PbS have demonstrated a high power conversion efficiency (PCE) of 10.82% (and independently certificated values of 10.62%), which is significantly higher than the PCE of 9.39% for PbO-PbS QD based ones. For the first time, systematic investigations are carried out on the effect of lead precursor engineering on the device performance. It is revealed that acetate can act as an efficient capping ligands together with oleic acid, providing better surface coverage and replace some of the harmful hydroxyl (OH) ligands during the synthesis. Then the acetate on the surface can be exchanged by iodide and lead to desired passivation. This work demonstrates that the precursor engineering has great potential in performance improvement. It is also pointed out that the initial synthesis is an often neglected but critical stage and has abundant room for optimization to further improve the quality of the resultant QDs, leading to breakthrough efficiency.

Room-Temperature Processed Nb2O5 as the Electron-Transporting Layer for Efficient Planar Perovskite Solar Cells.

In this work, we demonstrate high-efficiency planar perovskite solar cells (PSCs), using room-temperature sputtered niobium oxide (Nb2O5) as the electron-transporting layer (ETL). Widely spread ETL-like TiO2 often requires high-temperature (>450 °C) sintering, which is not desired for the fabrication of flexible devices. The amorphous Nb2O5 (labeled as a-Nb2O5) ETL, without any heat treatment, can give a best power conversion efficiency (PCE) of 17.1% for planar PSCs. Interestingly, the crystalline Nb2O5 (labeled as c-Nb2O5), with high-temperature (500 °C) annealing, results in a very similar PCE of 17.2%, indicating the great advantage of a-Nb2O5 in energy saving. We thus carried out a systematical investigation on the properties of the a-Nb2O5 film. The Hall effect measurements indicate both high mobility and conductivity of the a-Nb2O5 film. Kelvin probe force microscopy measurements define the Fermi levels of a-Nb2O5 and c-Nb2O5 as -4.31 and -4.02 eV, respectively, which allow efficient electron extraction at the Nb2O5/perovskite interface, regardless of the additional heat treatment on Nb2O5 film. Benefitting from the low-temperature process, we further demonstrated flexible PSCs based on a-Nb2O5, with a considerable PCE of 12.1%. The room-temperature processing and relatively high device performance of a-Nb2O5 suggest a great potential for its application in optoelectrical devices.

Epidemiology and temporal trend of suicide mortality in the elderly in Jiading, Shanghai, 2003-2013: a descriptive, observational study.

OBJECTIVES: To investigate and describe the epidemiological characteristics of suicide in the elderly in Jiading, Shanghai, for the period 2003-2013. DESIGN: Retrospective, observational, epidemiological study using routinely collected data. SETTING: Jiading District, Shanghai. METHODS: Suicide data were retrieved from the Shanghai Vital Registry database for the period 2003-2013. Crude and age-standardised mortality rates were calculated for various groups according to sex and age. Joinpoint regression was performed to estimate the percentage change (PC) and annual percentage change (APC) for suicide mortality. RESULT: A total of 956 deaths due to suicide occurred among people aged ≥65 years during the study period, accounting for 76.7% (956/1247) of all suicide decedents. Among the 956 people with suicide deaths, 88.7% (848/956) had a history of a psychiatric condition. The age-standardised mortality rates for suicide without and with a psychotic history in people aged ≥65 years were much higher than those for people aged <65 years in both genders. Suicide mortality in the elderly showed a declining trend, with a PC of -51.5% for men and -47.5% for women. The APC was -29.1 in 2003-2005, 4.6 in 2005-2008 and -9.7 in 2008-2013 for aged men, and -12.2 in 2003-2006 and -5.2 in 2006-2013 for aged women, respectively. Women living in Jiading had a higher risk of suicide death than men, especially among the elderly. The mortality rate for suicide increased with age in the elderly, and was more marked for those with a psychiatric history than for those without. CONCLUSIONS: Suicide mortality declined in Jiading during the study period 2003-2013 overall, but remained high in the elderly, especially those with a psychiatric history.

High efficiency all-polymer tandem solar cells.

In this work, we have reported for the first time an efficient all-polymer tandem cell using identical sub-cells based on P2F-DO:N2200. A high power conversion efficiency (PCE) of 6.70% was achieved, which is among the highest efficiencies for all polymer solar cells and 43% larger than the PCE of single junction cell. The largely improved device performance can be mainly attributed to the enhanced absorption of tandem cell. Meanwhile, the carrier collection in device remains efficient by optimizing the recombination layer and sub-cell film thickness. Thus tandem structure can become an easy approach to effectively boost the performance of current all polymer solar cells.

Impact evaluation of a community-based intervention to reduce risky sexual behaviour among female sex workers in Shanghai, China.

BACKGROUND: Female sex workers (FSWs) are at risk for sexually transmitted infections (STIs), including HIV. We implemented an HIV/STI preventive intervention among FSWs in Shanghai that aimed to increase condom use, improve HIV knowledge, and reduce STI and HIV incidence. METHODS: From six districts in Shanghai, 750 randomly selected venue-based FSWs were allocated to either a behavioural intervention or control group. In the intervention and control groups, 221 and 278 participants, respectively, had at least one follow-up at three or six months. In analysis, we randomly selected 57 lost to follow-up cases in the intervention group and imputed baseline values to equalize the arms at n = 278 (74.1% follow-up rate in each group). The impacts of the intervention on condom use, HIV/STI risk perception and knowledge, and STI incidence were assessed using either a logistic or linear model, adjusting for the baseline measure of the outcome and venue type. RESULTS: The intervention improved consistent condom use with any partner type in the previous month (AOR = 2.09, 95% CI, 1.43-3.04, p = 0.0001). Consistent condom use with clients in the three most recent sex acts increased in both arms, and with primary partners in the intervention arm, but there was no difference between groups after adjusting for baseline condom use and venue type. There were no differences in cumulative incidence of any STI (i.e., chlamydia, gonorrhoea, syphilis) between groups. HIV transmission knowledge (p = 0.0001), condom use skill (p = 0.0421), and self-efficacy for using condoms (p = 0.0071) were improved by the intervention. HIV-related stigma declined (p = 0.0119) and HIV and STI risk perception were improved (4.6 to 13.9%, and 9.4 to 20.0%, respectively). The intervention was associated with these improvements after adjusting for the baseline measure and venue type. CONCLUSION: Following a preventive intervention among Shanghai FSWs, our findings demonstrate that a simple, community-based educational intervention improved overall condom use, HIV and STI knowledge, and attitudes in relation to HIV/AIDS. The intervention should be implemented widely after tailoring educational materials regarding condom negotiation with different partner types (i.e., commercial sex clients and primary partners).