RESUMO
We analyze the stability and photophysical dynamics of CsPbBr3 perovskite quantum dots (PeQDs), fabricated under mild synthetic conditions and embedded in an amorphous silica (SiOx) matrix (CsPbBr3@SiOx), underscoring their sustained performance in ambient conditions for over 300 days with minimal optical degradation. However, this stability comes at the cost of a reduced photoluminescence efficiency. Time-resolved spectroscopic analyses, including flash-photolysis time-resolved microwave conductivity and time-resolved photoluminescence, show that excitons in CsPbBr3@SiOx films decay within 2.5 ns, while charge carriers recombine over approximately 230 ns. This longevity of the charge carriers is due to photoinduced electron transfer to the SiOx matrix, enabling hole retention. The measured hole mobility in these PeQDs is 0.880 cm2 V-1 s-1, underscoring their potential in optoelectronic applications. This study highlights the role of the silica matrix in enhancing the durability of PeQDs in humid environments and modifying exciton dynamics and photoluminescence, providing valuable insights for developing robust optoelectronic materials.
RESUMO
In this study, we present a novel method for controlling the growth of perovskite crystals in the vacuum thermal evaporation process by utilizing a vacuum-processable additive, propylene urea (PU). By coevaporation of perovskite precursors with PU to form the perovskite layer, PU, acting as a Lewis base additive, retards the direct reaction between the perovskite precursors. This facilitates a larger domain size and reduced defect density. Following the removal of the residual additive, the perovskite layer, exhibiting improved crystallinity, demonstrates reduced charge recombination, as confirmed by a time-resolved microwave conductivity analysis. Consequently, there is a notable enhancement in open-circuit voltage and power conversion efficiency, increasing from 1.05 to 1.15 V and from 17.17 to 18.31%, respectively. The incorporation of a vacuum-processable and removable Lewis base additive into the fabrication of vacuum-processed perovskite solar cells offers new avenues for optimizing these devices.
RESUMO
Although previous studies have examined the signaling pathway involved in melanogenesis through which ultraviolet (UV) or α-melanocyte-stimulating hormones (α-MSH) stimuli act as key inducers to produce melanin at the stratum basal layer of the epidermis, the signaling pathway regulating melanogenesis is still controversial. This study reports that α-MSH, not UVA and UVB, acted as a major stimulus of melanogenesis in B16F10 melanoma cells. Signaling pathway analysis using gene knockdown technology and chemical inhibitors, the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK)/p90 ribosomal S6 kinase 2 (RSK2) played an important role in melanogenesis. Unexpectedly, LY294002, a PI3K inhibitor, increased melanogenesis without UV or α-MSH stimulation, suggesting that the PI3K/AKT signaling pathway may not be a major signaling pathway for melanogenesis. Chemical inhibition of the MEKs/ERKs/RSK2 signaling pathway using U0126 or BI-D1870 suppressed melanogenesis by stimulation of UVA or α-MSH stimulation, or both. In particular, the genetic depletion of RSK2 or constitutive active (CA)-RSK2 overexpression showed that RSK2 plays a key role in melanogenesis. Interestingly, forkhead box protein O4 (FOXO4) was phosphorylated by RSK2, resulting in the increase of FOXO4's transactivation activity. Notably, the FOXO4 mutant harboring serine-to-alanine replacement at the phosphorylation sites totally abrogated the transactivation activity and reduced melanin production, indicating that RSK2-mediated FOXO4 activity plays a key role in melanogenesis. Furthermore, kaempferol, a flavonoid inhibiting the RSK2 activity, suppressed melanogenesis. In addition, FOXO4-wt overexpression showed that FOXO4 enhance melanin synthesis. Overall, the RSK2-FOXO4 signaling pathway plays a key role in modulating melanogenesis.