Managing Excess Lead Iodide with Functionalized Oxo‐Graphene Nanosheets for Stable Perovskite Solar Cells

Stability issues could prevent lead halide perovskite solar cells (PSCs) from commercialization despite it having a comparable power conversion efficiency (PCE) to silicon solar cells. Overcoming drawbacks affecting their long-term stability is gaining incremental importance. Excess lead iodide (PbI2) causes perovskite degradation, although it aids in crystal growth and defect passivation. Herein, we synthesized functionalized oxo-graphene nanosheets (Dec-oxoG NSs) to effectively manage the excess PbI2. Dec-oxoG NSs provide anchoring sites to bind the excess PbI2 and passivate perovskite grain boundaries, thereby reducing charge recombination loss and significantly boosting the extraction of free electrons. The inclusion of Dec-oxoG NSs leads to a PCE of 23.7 % in inverted (p-i-n) PSCs. The devices retain 93.8 % of their initial efficiency after 1,000 hours of tracking at maximum power points under continuous one-sun illumination and exhibit high stability under thermal and ambient conditions

Normalized multibump solutions to nonlinear Schrödinger equations with steep potential well

Abstract We are concerned with the existence of multibump solutions to the nonlinear Schrödinger equation − Δ u + λ a ( x ) u + μ u = | u | 2 σ u in R N with an L 2-constraint ‖ u ‖ L 2 ( R N ) 2 = ρ in the L 2-subcritical case σ ∈ (0, 2/N) and the L 2-supercritical case σ ∈ (2/N, 2*/N), where the usual critical Sobolev exponent is 2* = +∞ if N = 1, 2 and 2* = 2N/(N − 2) if N ⩾ 3. Here μ ∈ R will arise as a Lagrange multiplier, and 0 ⩽ a ∈ L loc ∞ ( R N ) has a bottom int a −1(0) composed of ℓ 0 (ℓ 0 ⩾ 1) connected components { Ω i } i = 1 ℓ 0 , where int a −1(0) is the interior of the zero set a − 1 ( 0 ) = { x ∈ R N | a ( x ) = 0 } of a. When ρ is fixed either large in the L 2-subcritical case or small in the L 2-supercritical case, we construct a ℓ-bump (1 ⩽ ℓ ⩽ ℓ 0) positive normalized solution which is localised at ℓ prescribed components { Ω i } i = 1 ℓ for large λ. The asymptotic profile of the solution is also analysed through taking the limit as λ → +∞, and subsequently as ρ → +∞ in the L 2-subcritical case or ρ → 0+ in the L 2-supercritical case. In particular, we find ℓ-bump normalized solutions to the related Dirichlet problem 0\quad \text{for}\ i=1,\dots ,\ell .\hfill \end{aligned}\right.\end{equation*}?> − Δ v + μ v = | v | 2 σ v , v ∈ H 0 1 ( ∪ i = 1 ℓ Ω i ) , ∑ i = 1 ℓ ∫

The Spatio-Temporal Variation of Vegetation and Its Driving Factors during the Recent 20 Years in Beijing

As the most important city in China, Beijing has experienced an economic soar, large-scale population growth and eco-environment changes in the last 20 years. Evaluating climate- and human-induced vegetation changes could reveal the relationship of vegetation-climate-human activities and provide important insights for the coordination of economic growth and environmental protection. Based on a long-term MODIS vegetation index dataset, meteorological data (temperature, precipitation) and impervious surface data, the Theil-Sen regression and the Mann-Kendall method are used to estimate vegetation change trends in this study and the residual analysis is utilized to distinguish the impacts of climate factors and human activities on vegetation restoration and degradation from 2000 to 2019 in Beijing. Our results show that the increasing vegetation areas account for 80.2% of Beijing. The restoration of vegetation is concentrated in the urban core area and mountainous area, while the degradation of vegetation is mainly concentrated in the suburbs. In recent years, the vegetation in most mountainous areas has changed from restoration to significant restoration, indicating that the growth of mountain vegetation has continued to restore. We also found that in the process of urban expansion, vegetation browning occurred in 53.1% of the urban built-up area, while vegetation greening occurred in the remaining area. We concluded that precipitation is the main climatic factor affecting the growth of vegetation in Beijing’s mountainous areas through correlation analysis. Human activities have significantly promoted the vegetation growth in the northern mountainous area thanks to the establishment of environmental protection areas. The negative correlation between vegetation and the impervious surface tends to gradually expand outwards, which is consistent with the trend of urban expansion. The positive correlation region remains stable, but the positive correlation is gradually enhanced. The response of vegetation to urbanization demonstrated a high degree of spatial heterogeneity. These findings indicated that human activities played an increasingly important role in influencing vegetation changes in Beijing