Solvent engineering based on triethylenetetramine (TETA) for perovskite solar cells processed in ambient-air

Solvent engineering as a crucial factor in determining the photovoltaic performance of perovskite solar cells has attracted much attention in recent years. Herein, we treat PbI2 and perovskite films with isopropyl alcohol, acetone, diethyl ether and dichloromethane, as standard solvents, in a modified two-step method. Meanwhile, triethylenetetramine (TETA) is introduced as a new reagent in solvent engineering for perovskite solar cell devices. Structural, optical and photovoltaic characteristics of the TETA-treated perovskite films are compared with those of the ones treated with different solvents. A shiny, pinhole-free and full-coverage texture with sufficiently large grain sizes is obtained in the presence of TETA, suggesting an efficient solvent engineering for perovskite layers. Moreover, the results reveal that residual PbI2 is completely removed and converted to a crystalline perovskite film. Amongst the PSC devices engineered with various solvents, the TETA-treated film exhibits a 55% increase in photoconversion efficiency compared to the control device with no solvent engineering.

The role of a vapor-assisted solution process on tailoring the chemical composition and morphology of mixed-halide perovskite solar cells

Herein, we report a modified two-step method to construct a uniform and pinhole-free polycrystalline perovskite film with large grains up to the microscale using lead mixed-halide (PbI₂–PbCl₂) precursor solutions to guarantee the device functioning.

Dissociable fronto-striatal effects of dopamine D2 receptor stimulation on cognitive versus motor flexibility

Genetic and pharmacological studies suggest an important role of the dopamine D2 receptor (DRD2) in flexible behavioral adaptation, mostly shown in reward-based learning paradigms. Recent evidence from imaging genetics indicates that also intentional cognitive flexibility, associated with lateral frontal cortex, is affected by variations in DRD2 signaling. In the present functional magnetic resonance imaging (MRI) study, we tested the effects of a direct pharmacological manipulation of DRD2 stimulation on intentional flexibility in a task-switching context, requiring switches between cognitive task rules and between response hands. In a double blind, counterbalanced design, participants received either a low dose of the DRD2 agonist bromocriptine or a placebo in two separate sessions. Bromocriptine modulated the blood-oxygen-level-dependent (BOLD) signal during rule switching: rule-switching-related activity in the left posterior lateral frontal cortex and in the striatum was increased compared to placebo, at comparable performance levels. Fronto-striatal connectivity under bromocriptine was slightly increased for rule switches compared to rule repetitions. Hand-switching-related activity, in contrast, was reduced under bromocriptine in sensorimotor regions. Our results provide converging evidence for an involvement of DRD2 signaling in fronto-striatal mechanisms underlying intentional flexibility, and indicate that the neural mechanisms underlying different types of flexibility (cognitive vs motor) are affected differently by increased dopaminergic stimulation.

1H MRSI of middle frontal gyrus in pediatric ADHD

Neuroimaging studies in multiple modalities have implicated the left or right dorsolateral prefrontal cortex (here, middle frontal gyrus) in attentional functions, in ADHD, and in dopamine agonist treatment of ADHD. The far lateral location of this cortex in the brain, however, has made it difficult to study with magnetic resonance spectroscopy (MRS). We used the smaller voxel sizes of the magnetic resonance spectroscopic imaging (MRSI) variant of MRS, acquired at a steep coronal-oblique angle to sample bilateral middle frontal gyrus in 13 children and adolescents with ADHD and 13 age- and sex-matched healthy controls. Within a subsample of the ADHD patients, aspects of attention were also assessed with the Trail Making Task. In right middle frontal gyrus only, mean levels of N-acetyl-aspartate + N-acetyl-aspartyl-glutamate (tNAA), creatine + phosphocreatine (Cr), choline-compounds (Cho), and myo-inositol (mI) were significantly lower in the ADHD than in the control sample. In the ADHD patients, lower right middle frontal Cr was associated with worse performance on Trails A and B (focused attention, concentration, set-shifting), while the opposite relationship held true for the control group on Trails B. These findings add to evidence implicating right middle frontal cortex in ADHD. Lower levels of these multiple species may reflect osmotic adjustment to elevated prefrontal cortical perfusion in ADHD and/or a previously hypothesized defect in astrocytic production of lactate in ADHD resulting in decelerated energetic metabolism (Cr), membrane synthesis (Cho, mI), and acetyl-CoA substrate for NAA synthesis. Lower Cr levels may indicate attentional or executive impairments.