2D materials for conducting holes from grain boundaries in perovskite solar cells

Grain boundaries in organic-inorganic halide perovskite solar cells (PSCs) have been found to be detrimental to the photovoltaic performance of devices. Here, we develop a unique approach to overcome this problem by modifying the edges of perovskite grain boundaries with flakes of high-mobility two-dimensional (2D) materials via a convenient solution process. A synergistic effect between the 2D flakes and perovskite grain boundaries is observed for the first time, which can significantly enhance the performance of PSCs. We find that the 2D flakes can conduct holes from the grain boundaries to the hole transport layers in PSCs, thereby making hole channels in the grain boundaries of the devices. Hence, 2D flakes with high carrier mobilities and short distances to grain boundaries can induce a more pronounced performance enhancement of the devices. This work presents a cost-effective strategy for improving the performance of PSCs by using high-mobility 2D materials

2D WSe2 Flakes for Synergistic Modulation of Grain Growth and Charge Transfer in Tin‐Based Perovskite Solar Cells

Abstract Tin (Sn)‐based perovskites with favorable optoelectronic properties and ideal bandgaps have emerged as promising alternatives to toxic lead (Pb)‐based perovskites for photovoltaic applications. However, it is challenging to obtain high‐quality Sn‐based perovskite films by solution process. Here, liquid‐exfoliated 2D transition‐metal dichalcogenides (i.e., MoS2, WS2, and WSe2) with smooth and defect‐free surfaces are applied as growth templates for spin‐coated FASnI3 perovskite films, leading to van der Waals epitaxial growth of perovskite grains with a growth orientation along (100). The authors find that WSe2 has better energy alignment with FASnI3 than MoS2 and WS2 and results in a cascade band structure in resultant perovskite solar cells (PSCs), which can facilitate hole extraction and suppress interfacial charge recombination in the devices. The WSe2‐modified PSCs show a power conversion efficiency up to 10.47%, which is among the highest efficiency of FASnI3‐based PSCs. The appealing solution phase epitaxial growth of FASnI3 perovskite on 2D WSe2 flakes is expected to find broad applications in optoelectronic devices

Micro-Nanoarchitectonics of Ga₂O₃/GaN Core-Shell Rod Arrays for High-Performance Broadband Ultraviolet Photodetection

This study presents broadband ultraviolet photodetectors (BUV PDs) based on Ga2O3/GaN core-shell micro-nanorod arrays with excellent performance. Micro-Nanoarchitectonics of Ga2O3/GaN core-shell rod arrays were fabricated with high-temperature oxidization of GaN micro-nanorod arrays. The PD based on the microrod arrays exhibited an ultrahigh responsivity of 2300 A/W for 280 nm at 7 V, the peak responsivity was approximately 400 times larger than those of the PD based on the planar Ga2O3/GaN film. The responsivity was over 1500 A/W for the 270–360 nm band at 7 V. The external quantum efficiency was up to 1.02 × 106% for 280 nm. Moreover, the responsivity was further increased to 2.65 × 104 A/W for 365 nm and over 1.5 × 104 A/W for 270–360 nm using the nanorod arrays. The physical mechanism may have been attributed to the large surface area of the micro-nanorods coupled with the Ga2O3/GaN heterostructure, which excited more photogenerated holes to be blocked at the Ga2O3 surface and Ga2O3/GaN interface, resulting in a larger internal gain. The overall high performance coupled with large-scale production makes it a promising candidate for practical BUV PD

Stabilization Effects of Inclined Soil–Cement Continuous Mixing Walls for Existing Warm Frozen Soil Embankments

Affected by climate warming and anthropogenic disturbances, the thermo-mechanical stability of warm and ice-rich frozen ground along the Qinghai–Tibet Railway (QTR) is continuously decreasing, and melting subsidence damage to existing warm frozen soil (WFS) embankments is constantly occurring, thus seriously affecting the stability and safety of the existing WFS embankments. In this study, in order to solve the problems associated with the melting settlement of existing WFS embankments, a novel reinforcement technology for ground improvement, called an inclined soil–cement continuous mixing wall (ISCW), is proposed to reinforce embankments in warm and ice-rich permafrost regions. A numerical simulation of a finite element model was conducted to study the freeze–thaw process and evaluate the stabilization effects of the ISCW on an existing WFS embankment of the QTR. The numerical investigations revealed that the ISCW can efficiently reduce the melt settlement in the existing WFS embankment, as well as increase the bearing capacity of the existing WFS embankment, making it favorable for improving the bearing ability of composite foundations. The present investigation breaks through the traditional ideas of “active cooling” and “passive protection” and provides valuable guidelines for the choice of engineering supporting techniques to stabilize existing WFS embankments along the QTR

High-Performance, Self-Powered Photodetectors Based on Perovskite and Graphene

An ideal photodetector must exhibit a fast and wide tunable spectral response, be highly responsive, have low power consumption, and have a facile fabrication process. In this work, a self-powered photodetector with a graphene electrode and a perovskite photoactive layer is assembled for the first time. The graphene electrode is prepared using a solution transfer process, and the perovskite layer is prepared using a solution coating process, which makes the device low cost. Graphene can form a Schottky junction with TiO₂ to efficiently separate/transport photogenerated excitons at the graphene/perovskite interface. Unlike the conventional photovoltaic structure, in this photodetector, both photogenerated electrons and holes are transported along the same direction to graphene, and electrons tunneled into TiO₂ are collected by the cathode and holes transported by graphene are collected by the anode; therefore, the photodetector is self-powered. The photodetector has a broad range of detection, from 260 to 900 nm, an ultrahigh on–off ratio of 4 × 10⁶, rapid response to light on–off (<5 ms), and a high level of detection of ∼10¹¹ Jones. The high performance is primarily due to the unique charge-transport property of graphene and strong light absorption properties of perovskite. This work suggests a new method for the production of self-powered photodetectors with high performance and low power consumption on a large scale