Mingzi Wang

Double perovskites Cs2AgSbCl6 have been synthesized via the solution state for applications as a promising photovoltaic absorber. Considering TiO2 as an electron transport layer (ETL), Cs2AgSbCl6/TiO2 heterojunction nanoparticles have also been prepared by the hydrothermal process to study the interface effect. Experimental measurements show that Cs2AgSbCl6 has a cubic structure with the lattice constant of 10.699 Å. The absorption peaks in the optical spectrum of the Ag and Sb-based double perovskites agree well with our density functional theory calculations. The Cs2AgSbCl6/TiO2 heterostructure exhibits enhanced optical absorption in the visible-light region compared to that of Cs2AgSbCl6, which is caused by the formation of the interface states and the decreased bandgap, thus facilitating the photo-induced optical transition in the visible-light region. From the charge transfer analysis of two interfaces (Ag2Sb2Cl8/TiO2 and Cs4Cl4/TiO2 interfaces), we find that the efficient separation of photo-induced carriers can be achieved at the Cs4Cl4/TiO2 interface, with electron flowing from the double perovskite layer to the TiO2 ETL, which is beneficial for improving the power conversion efficiency of solar cells. The combined study of theory and experiments indicates that the double perovskites Cs2AgSbCl6 would be a promising light-absorbing material in contact with TiO2 for the lead-free perovskite-based solar cell devices.

Abstract Defects in perovskite films are still the dominant destroyer of both power conversion efficiency (PCE) and long‐term stability in perovskite solar cells (PSCs). As the most popular electron transport layer (ETL), TiO 2 film is used in many PSCs to achieve high PCE. However, pristine TiO 2 by itself is not sufficient as an ETL due to lattice mismatch, poor alignment of the energy level gap, and hysteresis of the PSC. Herein, ammonium sulfamate (AS), with desired NH 4 + and S═O functional groups, is designed to modify the TiO 2 surface and interface to improve the PCE of PSCs. It is found that the AS works like a seed layer for the perovskite deposition, and, in addition, it effectively forms a bridge between the TiO 2 surface and the perovskite. As a result, PSCs are successfully fabricated with a champion power conversion efficiency of 24.78% with smaller hysteresis. The PSCs prepared using the AS‐modified TiO 2 also show excellent stability, and the bare device without any encapsulation retains 96% of its initial PCE after 1056 h of ambient exposure at 25 °C and 25% relative humidity.

Abstract It is a crucial role for enhancing the power conversion efficiency (PCE) of perovskite solar cells (PSCs) to prepare high‐quality perovskite films, which can be achieved by delaying the crystallization of perovskite film. Hence, we designed difluoroacetic anhydride (DFA) as an additive to regulating crystallization process thus reducing defect formation during perovskite film formation. It was found DFA reacts with DMSO by forming two molecules, difluoroacetate thioether ester (DTE) and difluoroacetic acid (DA). The strong bonding DTE ⋅ PbI 2 and DA ⋅ PbI 2 retard perovskite crystallization process for high‐quality film formation, which was monitored through in situ UV/Vis and PL tests. By using DFA additives, we prepared perovskite films with high‐quality and low defects. Finally, a champion PCE of 25.28 % was achieved with excellent environmental stability, which retained 95.75 % of the initial PCE after 1152 h at 25 °C under 25 % RH.

Deep underground projects (e.g., coal mines), are often faced with complex conditions such as high stress and extremely soft rock. The strength and rigidity of the traditional support system are often insufficient, which makes it difficult to meet the requirements of ground control under complex conditions. As a new support form with high strength and rigidity, the confined concrete arch plays an important role in controlling the rock deformation under complex conditions. The section shape of the tunnel has an important impact on the mechanical properties and design of the support system. However, studies on the mechanical properties and influence mechanism of the new confined concrete arch are rarely reported. To this end, the mechanical properties of traditional U-shaped steel and new confined concrete arches is compared and comparative tests on arches of circular and straight-leg semicircular shapes in deep tunnels are conducted. A large mechanical testing system for underground engineering support structure is developed. The mechanical properties and influence mechanism of confined concrete arches with different section shapes under different loading modes and cross-section parameters are systematically studied. Test results show that the bearing capacity of the confined concrete arch is 2.10 times that of the U-shaped steel arch, and the bearing capacity of the circular confined concrete arch is 2.27 times that of the straight-leg semicircular arch. Among the various influencing factors and their engineering parameters, the lateral stress coefficient has the greatest impact on the bearing capacity of the confined concrete arch, followed by the steel pipe wall thickness, steel strength, and core concrete strength. Subsequently, the economic index of bearing capacity and cost is established, and the optimization design method for the confined concrete arch is proposed. Finally, this design method is applied to a high-stress tunnel under complex conditions, and the deformation of the surrounding rock is effectively controlled.