Opportunities and challenges in perovskite-organic thin-film tandem solar cells.

Efficiency is paramount in enhancing the performance and cost-effectiveness of solar cells. Recent advancements in single-junction perovskite solar cells (PSCs) have yielded an impressive efficiency of 26.1%, nearing their theoretical limit. Meanwhile, multi-junction tandem solar cells exhibit a remarkable efficiency potential exceeding 42%, surpassing the 33% limit of single-junction cells, thereby opening avenues for ultra-high-efficiency solar cells. Tandem solar cells (TSCs) represent a groundbreaking photovoltaic technology, offering high efficiency, low cost, and a simple fabrication process. Among various TSCs, perovskite-organic TSCs (PO TSCs) are particularly promising due to their ability to leverage the complementary strengths of PSCs and organic solar cells (OSCs). PO TSCs are poised to outperform existing TSCs in terms of device performance, manufacturing cost, and diverse applications. The introduction of Y6-series non-fullerene acceptors (NFAs) over the past three years has significantly advanced the development of OSCs, leading to remarkable progress in PO TSCs. This paper commences by elucidating the advantages and potential of OSCs as bottom sub-cells in PO TSCs, followed by an in-depth review of mainstream interconnection layer (ICL) design. It then addresses key challenges in wide bandgap PSCs, including phase segregation, photovoltage loss, energy loss, and long-term stability. The paper concludes by examining critical factors influencing the future development of PO TSCs.

Anion-π interactions suppress phase impurities in FAPbI3 solar cells.

Achieving both high efficiency and long-term stability is the key to the commercialization of perovskite solar cells (PSCs)1,2. However, the diversity of perovskite (ABX3) compositions and phases makes it challenging to fabricate high-quality films3-5. Perovskite formation relies on the reaction between AX and BX2, whereas most conventional methods for film-growth regulation are based solely on the interaction with the BX2 component. Herein, we demonstrate an alternative approach to modulate reaction kinetics by anion-π interaction between AX and hexafluorobenzene (HFB). Notably, these two approaches are independent but work together to establish 'dual-site regulation', which achieves a delicate control over the reaction between AX and BX2 without unwanted intermediates. The resultant formamidinium lead halides (FAPbI3) films exhibit fewer defects, redshifted absorption and high phase purity without detectable nanoscale δ phase. Consequently, we achieved PSCs with power conversion efficiency (PCE) up to 26.07% for a 0.08-cm2 device (25.8% certified) and 24.63% for a 1-cm2 device. The device also kept 94% of its initial PCE after maximum power point (MPP) tracking for 1,258 h under full-spectrum AM 1.5 G sunlight at 50 ± 5 °C. This method expands the range of chemical interactions that occur in perovskite precursors by exploring anion-π interactions and highlights the importance of the AX component as a new and effective working site to improved photovoltaic devices with high quality and phase purity.

Anion Confinement for Homogeneous Mixed Halide Perovskite Film Growth by Electrospray.

Wide-bandgap perovskites are promising absorbers for state-of-the-art tandem solar cells to feasibly surpass Shockley-Queisser limit with low cost. However, the commonly used mixed halide perovskites suffer from poor stability; particularly, photoinduced phase segregation. Electrospray deposition is developed to bridge the gap of growth rate between iodide and bromide components during film growth by spatially confining the anion diffusion and eliminating the kinetic difference, which universally improves the initial homogeneity of perovskite films regardless of device architectures. It thus promotes the efficiency and stability of corresponding solar cells based on wide-bandgap (1.68 eV) absorbers. Remarkable power conversion efficiencies (PCEs) of 21.44% and 20.77% are achieved in 0.08 cm2 and 1.0 cm2 devices, respectively. In addition, these devices maintain 90% of their initial PCE after 1550 h of stabilized power output (SPO) tracking upon one sun irradiation (LED) at room temperature.

Inhibited Crack Development by Compressive Strain in Perovskite Solar Cells with Improved Mechanical Stability.

Metal halide perovskites are promising as next-generation photovoltaic materials, but stability issues are still a huge obstacle to their commercialization. Here, the formation and evolution of cracks in perovskite films during thermal cycling, which affect their mechanical stability, are investigated. Compressive strain is employed to suppress cracks and delamination by in situ formed polymers with low elastic modulus during crystal growth. The resultant devices pass the thermal-cycling qualification (IEC61215:2016), retaining 95% of the initial power conversion efficiency (PCE) and compressive strain after 230 cycles. Meanwhile, the p-i-n devices deliver PCEs of 23.91% (0.0805 cm2 ) and 23.27% (1 cm2 ). The findings shed light on strain engineering with respect to their evolution, which enables mechanically stable perovskite solar cells.

The Diagnostic Value of Circulating VEGF in Diabetic Retinopathy in Asia: A Systematic Review and Meta-analysis.

PURPOSE: Vascular endothelial growth factor (VEGF) has obvious clinical value in diabetes, but the conclusions on the diagnostic value of diabetic retinopathy (DR) are not consistent. This study aims to comprehensively evaluate the accuracy of circulating VEGF in the diagnosis of DR in the Asian population by a method of meta-analysis. METHODS: PubMed, Cochrane Library, Embase, Web of Science, China National Knowledge Infrastructure (CNKI), and China Wanfang Databases were searched for relevant studies on the diagnostic value of VEGF for DR in Asia up to November 2021. The pooled sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), and areas under the curve (AUC) were calculated by Stata 15.0 software. RESULTS: After screening, eight eligible studies were enrolled, including 547 patients with DR. The results of the meta-analysis showed that the pooled DOR, sensitivity, specificity, PLR, and NLR were 31.67 (95%CI: 13.55 ~ 74.05), 0.86 (95%CI: 0.74 ~ 0.93), 0.84 (95%CI: 0.80 ~ 0.87), 5.33 (95%CI: 4.09 ~ 6.93), 0.17 (95%CI: 0.09 ~ 0.32), respectively. The AUC was 0.86 (95%CI: 0.82 ~ 0.89). CONCLUSION: Circulating VEGF has a good diagnostic value in DR in the Asian population, with the potential to be an early diagnostic marker for DR.

Initializing film homogeneity to retard phase segregation for stable perovskite solar cells.

The mixtures of cations and anions used in hybrid halide perovskites for high-performance solar cells often undergo element and phase segregation, which limits device lifetime. We adapted Schelling's model of segregation to study individual cation migration and found that the initial film inhomogeneity accelerates materials degradation. We fabricated perovskite films (FA1-xCsxPbI3; where FA is formamidinium) through the addition of selenophene, which led to homogeneous cation distribution that retarded cation aggregation during materials processing and device operation. The resultant devices achieved enhanced efficiency and retained >91% of their initial efficiency after 3190 hours at the maximum power point under 1 sun illumination. We also observe prolonged operational lifetime in devices with initially homogeneous FACsPb(Br0.13I0.87)3 absorbers.

Reversible Phase Transition for Durable Formamidinium-Dominated Perovskite Photovoltaics.

Phase instability is one of the major obstacles to the wide application of formamidinium (FA)-dominated perovskite solar cells (PSCs). An in-depth investigation on relevant phase transitions is urgently needed to explore more effective phase-stabilization strategies. Herein, the reversible phase-transition process of FA1- x Csx PbI3 perovskite between photoactive phase (α phase) and non-photoactive phase (δ phase) under humidity, as well as the reversible healing of degraded devices, is monitored. Moreover, through in situ atomic force microscopy, the kinetic transition between α and δ phase is revealed to be the "nucleation-growth transition" process. Density functional theory calculation implies an enthalpy-driven α-to-δ degradation process during humidity aging and an entropy-driven δ-to-α healing process at high temperatures. The α phase of FA1- x Csx PbI3 can be stabilized at elevated temperature under high humidity due to the increased nucleation barrier, and the resulting non-encapsulated PSCs retain >90% of their initial efficiency after >1000 h at 60 °C and 60% relative humidity. This finding provides a deepened understanding on the phase-transition process of FA1- x Csx PbI3 from both thermodynamics and kinetics points of view, which also presents an effective means to stabilize the α phase of FA-dominated perovskites and devices for practical applications.

Establishment of a Nomogram Model for Predicting Cardiovascular and Cerebrovascular Events in Diabetic Nephropathy Patients Receiving Maintenance Hemodialysis.

Objective: The objective of this study is to explore the risk factors of cardiovascular and cerebrovascular events (CCE) in patients with diabetic nephropathy (DN) receiving maintenance hemodialysis, and to establish a nomogram model on this basis. Method: 144 patients with DN receiving maintenance hemodialysis from February 2020 to February 2021 were selected and followed up for 12 months. They were divided into the occurrence and nonoccurrence groups according to whether CCE occurred. The multivariate logistic regression analysis was used to analyze the influencing factors of CCE, and a predictive nomogram model was established. The receiver operating characteristic (ROC) curve was drawn to evaluate the predictive effect of the nomogram model. The Hosmer-Lemeshow method was used to test the calibration degree. Results: Among the patients, 63 patients (43.75%) encountered CCE. Multivariate logistic regression analysis showed that age >60 years old, history of CCE, dialysis age >12 months, systolic blood pressure >140 mmHg, blood phosphorus level >1.5 mmol/L, triglyceride (TG) level >2.30 mmol/l, adiponectin (ADPN) level <5 mg/L, high-sensitivity-C-reactive protein (hs-CRP) level >10 mg/L, hemoglobin (Hb) level <120 g/L, serum creatinine (SCr) level >720 µmol/L, and albumin (ALB) level <40 g/L were independent risk factors for CCE. Based on the above independent risk factors, a nomogram model of CCE was created. ROC curve analysis showed that the area under curve for predicting CCE was 0.881 (95% CI: 0.833~0.919), indicating that the nomogram model had great predictive effect. The Hosmer-Lemeshow method showed that the calibration curve was in good agreement with the standard curve. Conclusion: Age, history of CCE, dialysis age, systolic blood pressure and serum phosphorus, and TG, ADPN, hs-CRP, Hb, SCr, and ALB levels are all influencing factors for the occurrence of CCE in patients with DN receiving maintenance hemodialysis, and the nomogram model has a great predictive effect on CCE.

Strain Modulation for Light-Stable n-i-p Perovskite/Silicon Tandem Solar Cells.

Perovskite/silicon tandem solar cells are promising to penetrate photovoltaic market. However, the wide-bandgap perovskite absorbers used in top-cell often suffer severe phase segregation under illumination, which restricts the operation lifetime of tandem solar cells. Here, a strain modulation strategy to fabricate light-stable perovskite/silicon tandem solar cells is reported. By employing adenosine triphosphate, the residual tensile strain in the wide-bandgap perovskite absorber is successfully converted to compressive strain, which mitigates light-induced ion migration and phase segregation. Based on the wide-bandgap perovskite with compressive strain, single-junction solar cells with the n-i-p layout yield a power conversion efficiency (PCE) of 20.53% with the smallest voltage deficits of 440 mV. These cells also maintain 83.60% of initial PCE after 2500 h operation at the maximum power point. Finally, these top cells are integrated with silicon bottom cells in a monolithic tandem device, which achieves a PCE of 26.95% and improved light stability at open-circuit.

Temperature-Insensitive Efficient Inorganic Perovskite Photovoltaics by Bulk Heterojunctions.

Inorganic perovskite solar cells (IPSCs) emerge as an ideal candidate for applications beyond terrestrial implementation due to their robustness. However, underlying mechanisms regarding their photovoltaic process at different temperatures remain unclear. Based on a stable absorber of CsPbI2.85 (BrCl)0.15 , considerable variation of corresponding device performance is revealed over temperature and further demonstrates a simple approach to an effective reduction of such variation. Interestingly, this absorber is found to be excitonic with poor carrier transport even at an ambient temperature of 285 K and below. With a novel device configuration of a PTB7-th/perovskite bulk heterojunction, exciton dissociation and carrier extraction is facilitated. The resultant solar cell attains a best power conversion efficiency (PCE) of 17.2% with the fill factor of ≈84%, which represents the highest-efficiency γ-phase IPSCs reported to date. Importantly, this device is less sensitive to operation temperature, wherein the PCE variation over the temperature range from 210 to 360 K is 60% suppressed compared with the reference. The approach is effectively extended to other IPSCs with different photoactive phases, which may shed light on realizing highly efficient IPSCs for specific scenarios such as polar regions, near-space, and exoplanet exploration.

Comparison of the Development and Prognosis in Patients of Hypertriglyceridemic Pancreatitis with and without Diabetes.

AIM: To investigate the clinical features and prognosis in patients of hyperlipidemic acute pancreatitis with or without diabetes. METHODS: 157 patients with hypertriglyceridemic pancreatitis (HTGP) were included in this study. Patients with a previous history of diabetes were identified in the group of HTGP with diabetes (HTGPD), while patients without a history of diabetes were identified in the group of HTGP. The clinical characteristics and prognosis data of these patients in the two groups were analyzed. RESULTS: Multivariate Cox regression analysis showed that age, body mass index, glycated serum protein (GSP), and Acute Physiology and Chronic Health Evaluation (APACHE) II score were significantly associated with mortality in patients with HTGP. The mortality was significantly higher in the HTGPD group than in the HTGP group (p < 0.001). Compared to patients of HTGP, those of HTGPD had older age of onset, higher blood glucose levels, and higher GSP levels on admission. Electrocardiograms showed that patients of HTGPD had a significantly higher risk of heart ischemia than those of HTGP (p < 0.05). Patients of HTGPD had higher APACHE II scores than those of HTGP (p < 0.001). Single-factor analysis showed that higher triglyceride levels, GSP, LDL, and previous history of diabetes were associated with HTGP recurrence. CONCLUSIONS: Clinicians should be alert to patients of HTGP with diabetes. Diabetes is an important risk factor for HTGP and hyperglycemia may affect the development and prognosis of HTGP.

Synergistic Effects of Eu-MOF on Perovskite Solar Cells with Improved Stability.

Enhancing device lifetime is one of the essential challenges in perovskite solar cells. The ultrathin Eu-MOF layer is introduced at the interface between the electron-transport layer and the perovskite absorber to improve the device stability. Both Eu ions and organic ligands in the MOF can reduce the defect concentration and improve carrier transport. Moreover, due to the Förster resonance energy transfer effect, Eu-MOF in perovskite films can improve light utilization and reduce the decomposition under ultraviolet light. Meanwhile, Eu-MOF also turns tensile strain to compressive strain in the perovskite films. As a result, the corresponding devices achieve a champion power conversion efficiency (PCE) of 22.16%. In addition, the devices retain 96% of their original PCE after 2000 h under the relative humidity of 30% and 91% of their original PCE after 1200 h after continuous 85 °C aging condition in N2 .

Liquid medium annealing for fabricating durable perovskite solar cells with improved reproducibility.

Solution processing of semiconductors is highly promising for the high-throughput production of cost-effective electronics and optoelectronics. Although hybrid perovskites have potential in various device applications, challenges remain in the development of high-quality materials with simultaneously improved processing reproducibility and scalability. Here, we report a liquid medium annealing (LMA) technology that creates a robust chemical environment and constant heating field to modulate crystal growth over the entire film. Our method produces films with high crystallinity, fewer defects, desired stoichiometry, and overall film homogeneity. The resulting perovskite solar cells (PSCs) yield a stabilized power output of 24.04% (certified 23.7%, 0.08 cm2) and maintain 95% of their initial power conversion efficiency (PCE) after 2000 hours of operation. In addition, the 1-cm2 PSCs exhibit a stabilized power output of 23.15% (certified PCE 22.3%) and keep 90% of their initial PCE after 1120 hours of operation, which illustrates their feasibility for scalable fabrication. LMA is less climate dependent and produces devices in-house with negligible performance variance year round. This method thus opens a new and effective avenue to improving the quality of perovskite films and photovoltaic devices in a scalable and reproducible manner.

Interfacial-engineering enhanced performance and stability of ZnO nanowire-based perovskite solar cells.

Perovskite solar cells (PSCs) have attracted extensive attention due to their convenient fabrication and excellent photoelectric characteristics. The highest power conversion efficiency (PCE) of over 25% has been realized. However, ZnO as electron transport layer based PSCs exhibit inferior PCE and stability because of the mismatched energy-band and undesirable interfacial recombination. Here, we introduce a thin layer of SnO2nanocrystals to construct an interfacial engineering with gradient energy band and interfacial passivation via a facile wet chemical process at a low temperature. The best PCE obtained in this study reaches 18.36%, and the stability is substantially improved and maintains a PCE of almost 100% over 500 h. The low-temperature fabrication process facilitates the future application of ZnO/SnO2-based PSCs in flexible and stretchable electronics.

Towards commercialization: the operational stability of perovskite solar cells.

Recently, perovskite solar cells (PSCs) have attracted much attention owing to their high power conversion efficiency (25.2%) and low fabrication cost. However, the short lifetime under operation is the major obstacle for their commercialization. With efforts from the entire PSC research community, significant advances have been witnessed to improve the device operational stability, and a timely summary on the progress is urgently needed. In this review, we first clarify the definition of operational stability and its significance in the context of practical use. By analyzing the mechanisms in established approaches for operational stability improvement, we summarize several effective strategies to extend device lifetime in a layer-by-layer sequence across the entire PSC. These mechanisms are discussed in the contexts of chemical reactions, photo-physical management, technological modification, etc., which may inspire future R&D for stable PSCs. Finally, emerging operational stability standards with respect to testing and reporting device operational stability are summarized and discussed, which may help reliable device stability data circulate in the research community. The main target of this review is gaining insight into the operational stability of PSCs, as well as providing useful guidance to further improve their operational lifetime by rational materials processing and device fabrication, which would finally promote the commercialization of perovskite solar cells.

Stacking Effects on Electron-Phonon Coupling in Layered Hybrid Perovskites via Microstrain Manipulation.

Organic-inorganic hybrid halide perovskites (ABX3), especially layered 2D perovskites, have been recognized as promising semiconductors due to their tunable crystal structure and unique optoelectronic properties. A-site cations, as spacers, allow various metal halide assemblies, but the stacking pattern and the influence of their collective behavior on the properties of the resultant materials remain ambiguous. Here, the cation-stacking effects in the 2D perovskite single crystals, with a focus on the electron-phonon interaction, are investigated. We reveal the different photoluminescence from the surface region and the interior of the crystal, which is due to the residual strain induced by A-site cation stacking. We also examine the cation-stacking effects on the electron-phonon interaction, which is further employed to tailor the optoelectronic properties of the resultant 2D crystals. By reducing the microstrain, we reduce the electron-phonon coupling to improve the mobility and their stability against electric field in the corresponding crystals. Our study suggests a way to manipulate the optoelectronic properties in 2D perovskite materials by rational design of cation stacking.

A two-step precise targeting nanoplatform for tumor therapy via the alkyl radicals activated by the microenvironment of organelles.

With the in-depth research of organelles, the microenvironment characteristics of their own, such as the acid environment of lysosomes and the high temperature environment of mitochondria, could be used as a natural and powerful condition for tumor therapy. Based on this, we constructed a two-step precise targeting nanoplatform which can realize the drug release and drug action triggered by the microenvironment of lysosomes (endosomes) and mitochondria, respectively. To begin with, the mesoporous silica nanoparticles (MSNs) were modified with triphenylphosphonium (TPP) and loaded with 2,2'-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride (AIPH). Then, folic acid (FA) targeted pH-sensitive liposomes containing docetaxel (Lipo/DTX-FA) were prepared by thin-film dispersion method, and the core-shell AIPH/MSN-TPP@Lipo/DTX-FA nanoparticles were constructed by self-assembly during the hydration of the liposomes. When this nanoplatform entered into the tumor cells through FA receptor-mediated endocytosis, the pH-sensitive liposomes were destabilized in the lysosomes, resulting in the release of DTX and AIPH/MSN-TPP nanoparticles. After that, AIPH was delivered to mitochondria by AIPH/MSN-TPP, and the alkyl radicals produced by AIPH under the high temperature environment can cause oxidative damage to mitochondria. Not only that, the DTX could enhance the anti-tumor effect of AIPH by downregulating the expression of anti-apoptotic Bcl-2 protein. The in vitro and in vivo results demonstrate that this delivery system could induce apoptosis based on organelles' s own microenvironment, which provides a new approach for tumor therapy.

An oral drug delivery system with programmed drug release and imaging properties for orthotopic colon cancer therapy.

Oral drug delivery systems (ODDSs) have attracted considerable attention in relation to orthotopic colon cancer therapy due to certain popular advantages. Unfortunately, their clinical applications are generally limited by the side-effects caused by systemic drug exposure and poor real-time monitoring capabilities. Inspired by the characteristics of pH changes of the gastrointestinal tract (GIT) and specific enzymes secreted by the colonic microflora, we anchored polyacrylic acid (PAA) and chitosan (CS) on Gd3+-doped mesoporous hydroxyapatite nanoparticles (Gd-MHAp NPs) to realize programmed drug release and magnetic resonance imaging (MRI) at the tumor sites. In particular, the grafted PAA, as a pH-responsive switch, could effect controlled drug release in the colon. Further, CS is functionalized as the enzyme-sensitive moiety, which could be degraded by ß-glycosidase in the colon. Gadolinium is a paramagnetic lanthanide element used in chelates, working as a contrast medium agent for an MRI system. Interestingly, after oral administration, CS and PAA could protect the drug-loaded nanoparticles (NPs) against variable physiological conditions in the GIT, allowing the drug to reach the colon tumor sites, preventing premature drug release. Enhanced drug concentrations at the colon tumor sites were achieved via this programmed drug release, which subsequently ameliorated the therapeutic effect. In addition, encapsulating both chemotherapeutic (5-fluorouracil, 5-FU) and targeted therapy drug (gefitinib, Gef) within Gd-MHAp NPs produced a synergistic therapeutic effect. In summary, this study demonstrated that such a novel drug system (Gd-MHAp/5-FU/Gef/CS/PAA NPs) could protect, transport, and program drug release locally within the colonic environment; further, this system exhibited a worthwhile therapeutic effect, providing a promising novel treatment strategy for orthotopic colon cancer.

Strain engineering in perovskite solar cells and its impacts on carrier dynamics.

The mixed halide perovskites have emerged as outstanding light absorbers for efficient solar cells. Unfortunately, it reveals inhomogeneity in these polycrystalline films due to composition separation, which leads to local lattice mismatches and emergent residual strains consequently. Thus far, the understanding of these residual strains and their effects on photovoltaic device performance is absent. Herein we study the evolution of residual strain over the films by depth-dependent grazing incident X-ray diffraction measurements. We identify the gradient distribution of in-plane strain component perpendicular to the substrate. Moreover, we reveal its impacts on the carrier dynamics over corresponding solar cells, which is stemmed from the strain induced energy bands bending of the perovskite absorber as indicated by first-principles calculations. Eventually, we modulate the status of residual strains in a controllable manner, which leads to enhanced PCEs up to 20.7% (certified) in devices via rational strain engineering.