Physical, hydraulic, and mechanical properties of clayey soil stabilized by Physical, hydraulic, and mechanical properties of clayey soil stabilized by lightweight alkali-activated slag geopolymer lightweight alkali-activated slag geopolymer Abstract Abstract Lightweight cement materials are extensively used in the infrastructure construction. Geopolymer is a low-carbon and environmentally friendly cementitious material. This paper presents an investigation on the physical, hydraulic, and mechanical characteristics of lightweight geopolymer stabilized soil (LGSS) and a comparison with lightweight cement stabilized soil (LCSS). Measurements of volumetric absorption (VA) of water, hydraulic conductivity (k), and unconfined compressive strength (qu), scanning electron microscope (SEM) observation, mercury intrusion porosimetry (MIP) test, and thermogravimetric analysis (TGA) are conducted. The results show that LGSS has higher VA than LCSS. The k of LGSS is one order of magnitude higher than that of LCSS. The qu of LGSS is 2-3.5 times of that of LCSS. Microstructurally, the VA and k of LGSS are found to be positively correlated with the volume of large air pores (>10 μm). Higher qu of LGSS than LCSS is attributed to more hydration products that fill up the voids of soil. It is concluded that LGSS gives better engineering performances than LCSS in terms of water absorption, permeability, and strength characteristics. Abstract: Lightweight cement materialsare extensively used in the infrastructure 5

of methylammonium iodide (MAI) with formamidine iodide (FAI) improves the structure stability of perovskite crystal and maximizes the short-circuit current density (J sc ) of PVSCs due to the lower bandgap of FAPbI 3 perovskite film, which significantly enhances the device stability and efficiency. [9][10][11] Recently, many works focus on minimizing the interfacial nonradiative recombination and further improving the efficiency of PVSCs by introducing passivation layers since the defect states on the perovskite surface is much larger than that in the perovskite bulk film. [12][13][14] In addition to the improvement of efficiency, the passivation layers also improve the stability of PVSCs by protecting the functional layers from external water or oxygen erosion and retraining ions' migration inside the devices. [15][16][17] The synergetic development of composition engineering, additive engineering, and interface engineering facilitates the charge transportation and reduces nonradiative recombination in the device, which leads to the enhancement of certified PCE up to 25.5%. [4,18,19] However, this efficiency still lags behind the theoretical efficiency defined by the Shockley-Queisser theory due to the severe nonradiative recombination losses inside devices, thus strategies are still needed to be developed to suppress the nonradiative recombination losses and further improve the device efficiency, especially for the open-circuit voltage (V oc ) while the J sc and fill factor (FF) are approaching the theoretical limit. [20][21][22] The V oc of PVSC is determined by the internal quasi-Fermi level splitting (QFLS) in the absorber layer. [22] The QFLS will reduce compared with the QFLS of the neat perovskite film when the charge transport layers (CTLs) attach to the perovskite layer, which is possibly induced by the mismatched energy level alignment between different layers and the defects at the perovskite/CTL interfaces. [23] The reduction of QFLS should be minimized as possible for fabrication of high-performance PVSCs as it leads to the reduction of V oc and efficiency. Thus, it is urging to reduce nonradiative recombination losses aroused by defects and mismatched energy level alignment between the perovskite layer and the CTLs so as to reduce the V oc loss.Theoretical simulations and experimental data show that the perovskite materials possess self-doping characteristic by The severe nonradiative recombination losses limit the further improvement of open-circuit voltage (V oc ) and power conversion efficiency (PCE) of perovskite solar cells (PVSCs). In this work, the 4,4′-cyclohexylidenebis [N,N-bis(4-methylphenyl) benzene amine] is dissolved into the antisolvent to prepare perovskite films, which reduces defects, improves the crystallinity, and induces a p/p + homojunction on the top surface of perovskite film. Besides, the 2-thiophenemethylammonium iodide and 2-thiophenethylammonium iodide form interface electric field and passivate defects on the bottom surface of perovskite film. The p/p + homojunction and...

Fiber is effective in restricting cracks and improving the toughness of geopolymer composites, but few studies have focused on the surface crack characteristics of fiber-reinforced geopolymer composites. In this paper, after flexural tests of polypropylene fiber-reinforced geopolymer mortar, the surface cracking image was collected by a digital camera and cracking information was extract by deep learning. Finally, the cracking and fractal characteristics were specifically discussed. The semantic segmentation network can accurately extract surface cracks for calculating various parameters. The results showed that the mean intersection over union (mIoU) and mean pixel accuracy (mPA) of the cracks are 0.8451 and 0.9213, respectively. Generally, the crack length, width, area, and fractal dimension of the specimen are all increased with the increase in the fiber volume fraction. These crack parameters grow rapidly when the fiber content is small, and the growth of the crack parameters gradually slows down as the fiber volume fraction increases to approximately 1.5%. The highest crack parameter values were found in the geopolymer mortar, with a 0.48 water–binder ratio and 12 mm fiber length. The variation of the bottom crack length and the side crack fractal dimension can be used to represent the overall crack variation patterns. Meanwhile, the crack parameters increase with the increased fiber factor in a quadratic function. Based on these crack parameters, the critical fiber factor and dense fiber factor of polypropylene fiber-reinforced geopolymer mortar were 200 and 550, respectively. They are greater than those of fiber-reinforced Portland cementitious composites. The influence of various crack parameters on the flexural strength is in the order of the crack area, width, length, and fractal dimension.

The energy loss (Eloss) aroused by inefficient charge transfer and large energy level offset at the buried interface of p‐i‐n perovskite solar cells (PVSCs) limits their development. In this work, a BF4− anion‐assisted molecular doping (AMD) strategy is first proposed to improve the charge transfer capability of hole transport layers (HTLs) and reduce the energy level offset at the buried interface of PVSCs. The AMD strategy improves the carrier mobility and density of poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl) amine] (PTAA) and poly[N,N′‐bis(4‐butilphenyl)‐N,N′‐bis(phenyl)‐benzidine] (Poly‐TPD) HTLs while lowering their Fermi levels. Meanwhile, BF4− anions regulate the crystallization and reduce donor‐type iodine vacancies, resulting in the energetics transformation from n‐type to p‐type on the bottom surface of perovskite film. The faster charge transfer and formed p–n homojunction reduce charge recombination and Eloss at the HTL/perovskite buried interface. The PVSCs utilizing AMD treated PTAA and Poly‐TPD as HTLs demonstrate a highest power conversion efficiency (PCE) of 24.26% and 22.65%, along with retaining 90.97% and 85.95% of the initial PCE after maximum power point tracking for 400 h. This work provides an effective way to minimize the Eloss at the buried interface of p‐i‐n PVSCs by accelerating charge transfer and forming p–n homojunctions.

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