Co-evaporation of metal halide perovskites by thermal evaporation is an attractive method since it does not require harmful solvents and enables precise control of the film thickness. Furthermore, the ability to manipulate the Fermi level allows the formation of a graded homojunction, providing interesting opportunities to improve the charge carrier collection efficiency. However, little is known about how these properties affect the charge carrier dynamics. In this work, the structural and optoelectronic properties of co-evaporated MAPbI3 films varying in thickness (100, 400, and 750 nm) with a gradient in composition are analyzed. The X-ray diffraction patterns show that excess PbI2 is only present in the thick layers. From X-ray photoelectron spectroscopy depth analysis, the I/Pb atomic ratio indicates methylammonium iodide deficiencies that become more prominent with thicker films, resulting in differently n-doped regions across the thick MAPbI3 films. We suggest that due to these differently n-doped regimes, an internal electric field is formed. Side-selective time-resolved microwave photo conductivity measurements show an elongation of the charge carrier lifetimes on increasing thickness. These observations can be explained by the fact that excess carriers separate under the influence of the electric field, preventing rapid decay in the thick films.

Recent progress of vapor-deposited perovskite solar cells (PSCs) has proved the feasibility of this deposition method in achieving promising photovoltaic devices. For the first time, it is probed the versatility of the co-evaporation process in creating perovskite layers customizable for different device architectures. A gradient of composition is created within the perovskite films by tuning the background chamber pressure during the growth process. This method leads to co-evaporated MAPbI₃ film with graded Fermi levels across the thickness. Here it is proved that this growth process is beneficial for p-i-n PSCs as it can guarantee a favorable energy alignment at the charge selective interfaces. Co-evaporated p-i-n PSCs, with different hole transporting layers, consistently achieve power conversion efficiency (PCE) over 20% with a champion value of 20.6%, one of the highest reported to date. The scaled-up p-i-n PSCs, with active areas of 1 and 1.96 cm², achieved the record PCEs of 19.1% and 17.2%, respectively, while the flexible PSCs reached a PCE of 19.3%. Unencapsulated PSCs demonstrate remarkable long-term stability, retaining ≈90% of their initial PCE when stored in ambient for 1000 h. These PSCs also preserve over 80% of their initial PCE after 500 h of thermal aging at 85 °C.

It is difficult to apply the structure of steel-ultra thin UHPC lightweight composite deck due to the adoption of the ultra-thin UHPC layer. To solve this problem, an innovative shear connector fabricated from short rebar is proposed. In this work, the shear performance of the short rebar connectors is revealed through static and fatigue tests on push-out specimens. The static tests disclosed that: ① Two failure modes, namely, the break of connector-to-steel deck weld and the localized damage of UHPC, were observed; ② The capacity of the short steel rebar increased with the length of the connector-to-steel deck weld; ③ The shear capacity of the short steel rebar was higher than that of headed stud, but it was lower than that of welded steel mesh. The fatigue tests showed that under a nominal shear stress range of 80 MPa, the fatigue lives of three specimens were 1.942, 2.710, and 1.958 million cycles, respectively. By removing the maximum value, the mean fatigue life of the remaining two specimens was 1.95 million cycles, which is slightly lower than 2 million, a value defined in related design specifications. Based on the fatigue theory of welded structures, the fatigue strength corresponding to a fatigue life of 2 million can be calculated as 79.6 MPa. Furthermore, a detailed finite-element analysis was performed to reveal the response of the proposed short rebar connectors on an orthotropic steel deck bridge. The analysis results indicated that when the spacing of the short rebar connector was 200×200 mm (longitudinal×transverse), both the connector and the connector-to-deck plate weld met the fatigue design requirement. The research results in this work provide theoretical basis for the application of real bridges in the future.

It is a huge challenge for high-tap-density electrodes to achieve high volumetric energy density but without compromising the ionic transportation. Herein, we prepared compact Li₄Ti₅O₁₂ (LTO) microspheres consisting of densely packed primary nanoparticles. The real space distribution of lithium ions inside the compact LTO was revealed by using scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) to identify the function of grain boundaries for lithium ion transportation during lithiation. The as-prepared LTO microspheres possess a high tap density (1.23 g cm^-3) and an ultra-small specific surface area (2.40 m² g^-1). Impressively, the compact LTO microspheres present excellent electrochemical performance. At high rates of 5C, 10C and 20C, the LTO microspheres show a specific capacity of 146.6, 138.2 and 111 mA h g^-1, respectively. The capacity retention remains at 97.8% at 5C after 500 cycles. The STEM-EELS results indicate that the lithiation reaction of LTO is firstly initiated at grain boundaries during the high rate lithiation process and then diffuses to the bulk area. The abundant grain boundaries in compact LTO microspheres can form a highly efficient conductive network to preferentially transport the ions, which contributes to high volumetric and gravimetric energy density simultaneously.