Improved charge extraction in inverted perovskite solar cells with dual-site-binding ligands.

Inverted (pin) perovskite solar cells (PSCs) afford improved operating stability in comparison to their nip counterparts but have lagged in power conversion efficiency (PCE). The energetic losses responsible for this PCE deficit in pin PSCs occur primarily at the interfaces between the perovskite and the charge-transport layers. Additive and surface treatments that use passivating ligands usually bind to a single active binding site: This dense packing of electrically resistive passivants perpendicular to the surface may limit the fill factor in pin PSCs. We identified ligands that bind two neighboring lead(II) ion (Pb2+) defect sites in a planar ligand orientation on the perovskite. We fabricated pin PSCs and report a certified quasi-steady state PCE of 26.15 and 24.74% for 0.05- and 1.04-square centimeter illuminated areas, respectively. The devices retain 95% of their initial PCE after 1200 hours of continuous 1 sun maximum power point operation at 65°C.

The dynamic adsorption affinity of ligands is a surrogate for the passivation of surface defects.

Surface defects in semiconducting materials, though they have been widely studied, remain a prominent source of loss in optoelectronic devices; here we sought a new angle of approach, looking into the dynamic roles played by surface defects under atmospheric stressors and their chemical passivants in the lifetime of optoelectronic materials. We find that surface defects possess properties distinct from those of bulk defects. ab initio molecular dynamics simulations reveal a previously overlooked reversible degradation mechanism mediated by hydrogen vacancies. We find that dynamic surface adsorption affinity (DAA) relative to surface treatment ligands is a surrogate for passivation efficacy, a more strongly-correlated feature than is the static binding strength emphasized in prior reports. This guides us to design targeted passivator ligands with high molecular polarity: for example, 4-aminobutylphosphonic acid exhibits strong DAA and provides defect passivation applicable to a range of perovskite compositions, including suppressed hydrogen vacancy formation, enhanced photovoltaic performances and operational stability in perovskite solar cells.

Anion optimization for bifunctional surface passivation in perovskite solar cells.

Pseudo-halide (PH) anion engineering has emerged as a surface passivation strategy of interest for perovskite-based optoelectronics; but until now, PH anions have led to insufficient defect passivation and thus to undesired deep impurity states. The size of the chemical space of PH anions (>106 molecules) has so far limited attempts to explore the full family of candidate molecules. We created a machine learning workflow to speed up the discovery process using full-density functional theory calculations for training the model. The physics-informed machine learning model allowed us to pinpoint promising molecules with a head group that prevents lattice distortion and anti-site defect formation, and a tail group optimized for strong attachment to the surface. We identified 15 potential bifunctional PH anions with the ability to passivate both donors and acceptors, and through experimentation, discovered that sodium thioglycolate was the most effective passivant. This strategy resulted in a power-conversion efficiency of 24.56% with a high open-circuit voltage of 1.19 volts (24.04% National Renewable Energy Lab-certified quasi-steady-state) in inverted perovskite solar cells. Encapsulated devices maintained 96% of their initial power-conversion energy during 900 hours of one-sun operation at the maximum power point.

Bilateral Gastrocnemius Tertius Muscles: Cadaveric Findings of a Rare Variant.

The posterior compartment of the leg typically contains three muscles in the superficial flexor group: the gastrocnemius, plantaris, and soleus. The gastrocnemius has medial and lateral heads (MH and LH) that originate from the medial and lateral condyles of the femur, respectively. However, a third head (TH) of the gastrocnemius, is a rare accessory muscle bundle of the gastrocnemius muscle that covers the surface of the popliteal fossa. Bilateral THs of gastrocnemius were identified in a 67-year-old male during a routine educational cadaveric dissection. Both gastrocnemius TH muscles consisted of a superficial belly with distinct neurovasculature heads and originated from the lateral condyle of the femur and inserted into the Achilles tendon. To our knowledge, the co-existence of bilateral gastrocnemius TH muscles has only been reported once. The male donor was found to exhibit an anatomical anomaly and could be clinically underdiagnosed due to its clinically silent nature and the lack of reports. Insight into the potential implications of bilateral and unilateral gastrocnemius TH and identification during clinical evaluation offers a path for future research to better identify and manage cases of gastrocnemius TH and its effects.

Engineering ligand reactivity enables high-temperature operation of stable perovskite solar cells.

Perovskite solar cells (PSCs) consisting of interfacial two- and three-dimensional heterostructures that incorporate ammonium ligand intercalation have enabled rapid progress toward the goal of uniting performance with stability. However, as the field continues to seek ever-higher durability, additional tools that avoid progressive ligand intercalation are needed to minimize degradation at high temperatures. We used ammonium ligands that are nonreactive with the bulk of perovskites and investigated a library that varies ligand molecular structure systematically. We found that fluorinated aniliniums offer interfacial passivation and simultaneously minimize reactivity with perovskites. Using this approach, we report a certified quasi-steady-state power-conversion efficiency of 24.09% for inverted-structure PSCs. In an encapsulated device operating at 85°C and 50% relative humidity, we document a 1560-hour T85 at maximum power point under 1-sun illumination.

Sterically Suppressed Phase Segregation in 3D Hollow Mixed-Halide Wide Band Gap Perovskites.

Band gap tuning in mixed-halide perovskites enables efficient multijunction solar cells and LEDs. However, these wide band gap perovskites, which contain a mixture of iodide and bromide ions, are known to phase segregate under illumination, introducing voltage losses that limit stability. Previous studies have employed inorganic perovskites, halide alloys, and grain/interface passivation to minimize halide segregation, yet photostability can be further advanced. By focusing on the role of halide vacancies in anion migration, one expects to be able to erect local barriers to ion migration. To achieve this, we employ a 3D "hollow" perovskite structure, wherein a molecule that is otherwise too large for the perovskite lattice is incorporated. The amount of hollowing agent, ethane-1,2-diammonium dihydroiodide (EDA), varies the density of the hollow sites. Photoluminescence measurements reveal that 1% EDA in the perovskite bulk can stabilize a 40% bromine mixed-halide perovskite at 1 sun illumination intensity. These, along with capacitance-frequency measurements, suggest that hollow sites limit the mobility of the halide vacancies.

Suppressed phase segregation for triple-junction perovskite solar cells.

The tunable bandgaps and facile fabrication of perovskites make them attractive for multi-junction photovoltaics1,2. However, light-induced phase segregation limits their efficiency and stability3-5: this occurs in wide-bandgap (>1.65 electron volts) iodide/bromide mixed perovskite absorbers, and becomes even more acute in the top cells of triple-junction solar photovoltaics that require a fully 2.0-electron-volt bandgap absorber2,6. Here we report that lattice distortion in iodide/bromide mixed perovskites is correlated with the suppression of phase segregation, generating an increased ion-migration energy barrier arising from the decreased average interatomic distance between the A-site cation and iodide. Using an approximately 2.0-electron-volt rubidium/caesium mixed-cation inorganic perovskite with large lattice distortion in the top subcell, we fabricated all-perovskite triple-junction solar cells and achieved an efficiency of 24.3 per cent (23.3 per cent certified quasi-steady-state efficiency) with an open-circuit voltage of 3.21 volts. This is, to our knowledge, the first reported certified efficiency for perovskite-based triple-junction solar cells. The triple-junction devices retain 80 per cent of their initial efficiency following 420 hours of operation at the maximum power point.

Regulating surface potential maximizes voltage in all-perovskite tandems.

The open-circuit voltage (VOC) deficit in perovskite solar cells is greater in wide-bandgap (over 1.7 eV) cells than in perovskites of roughly 1.5 eV (refs. 1,2). Quasi-Fermi-level-splitting measurements show VOC-limiting recombination at the electron-transport-layer contact3-5. This, we find, stems from inhomogeneous surface potential and poor perovskite-electron transport layer energetic alignment. Common monoammonium surface treatments fail to address this; as an alternative, we introduce diammonium molecules to modify perovskite surface states and achieve a more uniform spatial distribution of surface potential. Using 1,3-propane diammonium, quasi-Fermi-level splitting increases by 90 meV, enabling 1.79 eV perovskite solar cells with a certified 1.33 V VOC and over 19% power conversion efficiency (PCE). Incorporating this layer into a monolithic all-perovskite tandem, we report a record VOC of 2.19 V (89% of the detailed balance VOC limit) and over 27% PCE (26.3% certified quasi-steady state). These tandems retained more than 86% of their initial PCE after 500 h of operation.

Binding Affinity of Concanavalin A to Native and Acid-Hydrolyzed Phytoglycogen Nanoparticles.

Phytoglycogen (PG) is a polysaccharide produced in the kernels of sweet corn as soft, highly branched, compact nanoparticles. Its tree-like or dendritic architecture, combined with a high-safety profile, makes PG nanoparticles attractive for use in biological applications, many of which rely on the association or binding of small biomolecules. We have developed a methodology to functionalize surface plasmon resonance (SPR) sensor surfaces with PG nanoparticles, and we demonstrate the utility of the PG-functionalized SPR sensor by measuring the binding affinity of the tetrameric concanavalin A (ConA) protein to both native PG nanoparticles and smaller, softer acid-hydrolyzed PG nanoparticles. We measure comparable values of the equilibrium association constant K for native and acid-hydrolyzed PG, with a slightly smaller value for the acid-hydrolyzed particles that we attribute to unfavorable lateral interactions between the tetrameric subunits of ConA due to the increase in surface curvature of the smaller acid-hydrolyzed PG particles. We also use infrared reflection-absorption spectroscopy (IRRAS) to show that ConA maintains a large fraction of its native conformation, and thus its bioactivity, upon binding to PG, representing an important step toward the realization of PG as a novel bioactive delivery vehicle.

Nanotransfection-based vasculogenic cell reprogramming drives functional recovery in a mouse model of ischemic stroke.

Ischemic stroke causes vascular and neuronal tissue deficiencies that could lead to substantial functional impairment and/or death. Although progenitor-based vasculogenic cell therapies have shown promise as a potential rescue strategy following ischemic stroke, current approaches face major hurdles. Here, we used fibroblasts nanotransfected with Etv2, Foxc2, and Fli1 (EFF) to drive reprogramming-based vasculogenesis, intracranially, as a potential therapy for ischemic stroke. Perfusion analyses suggest that intracranial delivery of EFF-nanotransfected fibroblasts led to a dose-dependent increase in perfusion 14 days after injection. MRI and behavioral tests revealed ~70% infarct resolution and up to ~90% motor recovery for mice treated with EFF-nanotransfected fibroblasts. Immunohistological analysis confirmed increases in vascularity and neuronal cellularity, as well as reduced glial scar formation in response to treatment with EFF-nanotransfected fibroblasts. Together, our results suggest that vasculogenic cell therapies based on nanotransfection-driven (i.e., nonviral) cellular reprogramming represent a promising strategy for the treatment of ischemic stroke.

The NF-κB subunit c-Rel stimulates cardiac hypertrophy and fibrosis.

Cardiac remodeling and hypertrophy are the pathological consequences of cardiovascular disease and are correlated with its associated mortality. Activity of the transcription factor NF-κB is increased in the diseased heart; however, our present understanding of how the individual subunits contribute to cardiovascular disease is limited. We assign a new role for the c-Rel subunit as a stimulator of cardiac hypertrophy and fibrosis. We discovered that c-Rel-deficient mice have smaller hearts at birth, as well as during adulthood, and are protected from developing cardiac hypertrophy and fibrosis after chronic angiotensin infusion. Results of both gene expression and cross-linked chromatin immunoprecipitation assay analyses identified transcriptional activators of hypertrophy, myocyte enhancer family, Gata4, and Tbx proteins as Rel gene targets. We suggest that the p50 subunit could limit the prohypertrophic actions of c-Rel in the normal heart, because p50 overexpression in H9c2 cells repressed c-Rel levels and the absence of cardiac p50 was associated with increases in both c-Rel levels and cardiac hypertrophy. We report for the first time that c-Rel is highly expressed and confined to the nuclei of diseased adult human hearts but is restricted to the cytoplasm of normal cardiac tissues. We conclude that c-Rel-dependent signaling is critical for both cardiac remodeling and hypertrophy. Targeting its activities could offer a novel therapeutic strategy to limit the effects of cardiac disease.

MeCP2 controls an epigenetic pathway that promotes myofibroblast transdifferentiation and fibrosis.

BACKGROUND & AIMS: Myofibroblast transdifferentiation generates hepatic myofibroblasts, which promote liver fibrogenesis. The peroxisome proliferator-activated receptor gamma (PPARgamma) is a negative regulator of this process. We investigated epigenetic regulation of PPARgamma and myofibroblast transdifferentiation. METHODS: Chromatin immunoprecipitation (ChIP) assays assessed the binding of methyl-CpG binding protein 2 (MeCP2) to PPARgamma and chromatin modifications that silence this gene. MeCP2(-/y) mice and an inhibitor (DZNep) of the epigenetic regulatory protein EZH2 were used in the carbon tetrachloride model of liver fibrosis. Liver tissues from mice were assessed by histologic analysis; markers of fibrosis were measured by quantitative polymerase chain reaction (qPCR). Reverse transcription PCR detected changes in expression of the microRNA miR132 and its target, elongated transcripts of MeCP2. Myofibroblasts were transfected with miR132; PPARgamma and MeCP2 expressions were analyzed by qPCR or immunoblotting. RESULTS: Myofibroblast transdifferentiation of hepatic stellate cells is controlled by a combination of MeCP2, EZH2, and miR132 in a relay pathway. The pathway is activated by down-regulation of miR132, releasing the translational block on MeCP2. MeCP2 is recruited to the 5' end of PPARgamma, where it promotes methylation by H3K9 and recruits the transcription repressor HP1alpha. MeCP2 also stimulates expression of EZH2 and methylation of H3K27 to form a repressive chromatin structure in the 3' exons of PPARgamma. Genetic and pharmacologic disruptions of MeCP2 or EZH2 reduced the fibrogenic characteristics of myofibroblasts and attenuated fibrogenesis. CONCLUSIONS: Liver fibrosis is regulated by an epigenetic relay pathway that includes MeCP2, EZH2, and miR132. Reagents that interfere with this pathway might be developed to reduce fibrogenesis in chronic liver disease.