The perovskite solar cells (PSCs) based on cesium lead bromide (CsPbBr 3 ) with outstanding environmental stability and low preparation cost are regarded as one of the most promising photovoltaic devices for commercial applications. However, the performance of CsPbBr 3 PSCs can be badly deteriorated by the intense charge recombination arising from the ionic defects at the grain boundaries of perovskite film. To cope with this issue, we adopt an amino acid of Llysine with two amino and one carboxyl groups as a chemical additive to incorporate into perovskite film to simultaneously anchor the uncoordinated Pb 2+ (Cs + ) and halogen ion defects. Further, the grain size of CsPbBr 3 perovskite is boosted from 688 to over 1000 nm after L-lysine incorporation as a result of the decreased nucleation rate and the sufficient growth of perovskite, which effectively reduce the grain boundaries for load defects. As expected, the optimized device achieves a best power conversion efficiency of 9.69% attributed to the remarkably reduced charge recombination and enhanced charge extraction arising from the efficient defects dual-passivation and enlarged grain size of perovskite film as well as the improved energy level alignment at the device interface after the introduction of L-lysine, which is elevated by 61.23% in comparison to 6.01% efficiency of the pristine one. Moreover, the unencapsulated device with L-lysine incorporation exhibits remarkable long-term stability in air with 80% RH at 25 °C and 0% RH at 80 °C as well as under continuous illumination conditions. This work provides an effective multifunctional additive for imperfection passivation and grain size enlargement of perovskite to build PSCs with high efficiency and stability.

The preparation of high‐quality perovskite films with low grain boundaries and defect states is a prerequisite for achieving high‐efficiency perovskite solar cells (PSCs) with good environmental stability. An effective additive engineering strategy has been developed for simultaneous defect passivation and crystal growth of CsPbBr3 perovskite films by introducing 1,3,5‐triazine‐2,4,6‐triamine (melamine) into the PbBr2 precursor solution. The resultant melamine–PbBr2 film has a loose, large‐grained structure and decreased crystallinity, which has a positive effect on the crystallization process of the perovskite as it retards the crystallization rate as a result of the interaction between melamine and lead ions. Additionally, the passivation by melamine gives a high‐quality CsPbBr3 perovskite film with fewer grain boundaries, lower defect densities, and better energy level matching is achieved by multistep liquid‐phase spin‐coating, which greatly suppresses the nonradiative recombination resulting from the defects and promotes charge extraction at the interface. A champion power conversion efficiency as high as 9.65 % with a promising open‐circuit voltage of 1.584 V is achieved for PSCs with an architecture of fluorine‐doped tin oxide/c‐TiO2/m‐TiO2/melamine‐added CsPbBr3/carbon‐based hole‐transporting layer. Furthermore, the unencapsulated melamine‐added CsPbBr3 PSC shows superior thermal and humidity stability in ambient air at 85 °C or 85 % relative humidity over 720 h.

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Abstract:The urban heat island (UHI) effect resulting from rapid urbanization generally has a negative impact on urban residents. Shijiazhuang, the capital of Hebei Province in China, was selected to assess surface thermal patterns and its correlation with Land Cover Types (LCTs). This study was conducted using Landsat TM images on the mesoscale level and airborne hyperspectral thermal images on the microscale level. Land surface temperature (LST) was retrieved from four scenes of Landsat TM data in the summer days to analyze the thermal spatial patterns and intensity of surface UHI (SUHI). Surface thermal characteristics were further examined by relating LST to percentage of imperious surface area (ISA%) and four remote sensing indices (RSIs), the Normalized Difference Vegetation Index (NDVI), Universal Pattern Decomposition method (VIUPD), Normalized Difference Built-up Index (NDBI) and Biophysical Composition Index (BCI). On the other hand, fives scenes of airborne TASI (Thermal Airborne Spectrographic Imager sensor) images were utilized to describe more detailed urban thermal characteristics of the downtown of Shijiazhuang city. Our results show that an obvious surface heat island effect OPEN ACCESSRemote Sens. 2015, 7 4805 existed in the study area during summer days, with a SUHI intensity of 2-4 °C. The analyses reveal that ISA% can provide an additional metric for the study of SUHI, yet its association with LST is not straightforward and this should a focus in future work. It was also found that two physically based indices, VIUPD and BCI, have the potential to account for the variation in urban LST. The results concerning on TASI indicate that diversity of impervious surfaces (rooftops, concrete, and mixed asphalt) contribute most to the SUHI, among all of the land cover features. Moreover, the effect of impervious surfaces on LST is complicated, and the composition and arrangement of land cover features may play an important role in determining the magnitude and intensity of SUHI. Overall, the analysis of urban thermal signatures at two spatial scales complement each other and the use of airborne imagery data with higher spatial resolution is helpful in revealing more details for understanding urban thermal environments.Keywords: urban heat island (UHI); land cover types (LCTs); impervious surface area (ISA); thermal airborne spectrographic imager (TASI)