Investigation of Interfacial Charge Transfer in Solution Processed Cs₂SnI₆ Thin Films

Cesium tin halide based perovskite Cs₂SnI₆ has been subjected to in-depth investigations owing to its potentiality toward the realization of environment benign Pb free and stable solar cells. In spite of the fact that Cs₂SnI₆ has been successfully utilized as an efficient hole transport material owing to its p-type semiconducting nature, however, the nature of the majority carrier is still under debate. Therefore, intrinsic properties of Cs₂SnI₆ have been investigated in detail to explore its potentiality as light absorber along with facile electron and hole transport. A high absorption coefficient (5 × 10⁴ cm^–1) at 700 nm indicates the penetration depth of 700 nm light to be 0.2 μm, which is comparable to conventional Pb based solar cells. Preparation of pure and CsI impurity free dense thin films with controllable thicknesses of Cs₂SnI₆ by the solution processable method has been reported to be difficult owing to its poor solubility. An amicable solution to circumvent such problems of Cs₂SnI₆ has been provided utilizing spray-coating in combination with spin-coating. The presence of two emission peaks at 710 and 885 nm in the prepared Cs₂SnI₆ thin films indicated coexistence of quantum dot and bulk parts which were further supported by transmission electron microscopy (TEM) investigations. Time-resolved photoluminescence (PL) and transient absorption spectroscopy (TAS) were employed to investigate the excitation carrier lifetime, which revealed fast decay kinetics in the picoseconds (ps) to nanoseconds (ns) time domains. Time-resolved microwave photoconductivity decay (MPCD) measurement provided the mobile charge carrier lifetime exceeding 300 ns, which was also in agreement with the nanosecond transient absorption spectroscopy (ns-TAS) indicating slow charge decay lasting up to 20 μs. TA assisted interfacial charge transfer investigations utilizing Cs₂SnI₆ in combination with n-type PCBM and p-type P3HT exhibited both intrinsic electron and hole transport

Data_Sheet_1_Exposure to urban green spaces and mental health during the COVID-19 pandemic: evidence from two low and lower-middle-income countries.docx

IntroductionThe COVID-19 pandemic has had a significant impact on mental health globally, with limited access to mental health care affecting low- and middle-income countries (LMICs) the most. In response, alternative strategies to support mental health have been necessary, with access to green spaces being a potential solution. While studies have highlighted the role of green spaces in promoting mental health during pandemic lockdowns, few studies have focused on the role of green spaces in mental health recovery after lockdowns. This study investigated changes in green space access and associations with mental health recovery in Bangladesh and Egypt across the pandemic.MethodsAn online survey was conducted between January and April 2021 after the first lockdown was lifted in Bangladesh (n = 556) and Egypt (n = 660). We evaluated indoor and outdoor greenery, including the number of household plants, window views, and duration of outdoor visits. The quantity of greenness was estimated using the normalized difference vegetation index (NDVI). This index was estimated using satellite images with a resolution of 10x10m during the survey period (January-April 2021) with Sentinel-2 satellite in the Google Earth Engine platform. We calculated averages within 250m, 300m, 500m and 1000m buffers of the survey check-in locations using ArcGIS 10.3. Multiple linear regression models were used to evaluate relationships between changes in natural exposure and changes in mental health.ResultsThe results showed that mental health improved in both countries after the lockdown period. People in both countries increased their time spent outdoors in green spaces after the lockdown period, and these increases in time outdoors were associated with improved mental health. Unexpectedly, changes in the number of indoor plants after the lockdown period were associated with contrasting mental health outcomes; more plants translated to increased anxiety and decreased depression. Refocusing lives after the pandemic on areas other than maintaining indoor plants may assist with worrying and feeling panicked. Still, indoor plants may assist with depressive symptoms for people remaining isolated.ConclusionThese findings have important implications for policymakers and urban planners in LMICs, highlighting the need to increase access to natural environments in urban areas to improve mental health and well-being in public health emergencies.</p