No abstract

Timely monitoring of pavement cracks is essential for successful maintenance of road infrastructure. Accurate information concerning crack location and severity enables proactive management of the infrastructure. Black‐box cameras, which are becoming increasingly widespread at an affordable price, can be used as efficient road‐image collectors over a wide area. However, the cracks in these images are difficult to detect, because the images containing them often include objects other than roads. Thus, we propose a pixel‐level detection method for identifying road cracks in black‐box images using a deep convolutional encoder–decoder network. The encoder consists of convolutional layers of the residual network for extracting crack features, and the decoder consists of deconvolutional layers for localizing the cracks in an input image. The proposed network was trained on 427 out of 527 images extracted from black‐box videos and tested on the remaining 100 images. Compared with VGG‐16, ResNet‐50, ResNet‐101, ResNet‐200 with transfer learning, and ResNet‐152 without transfer learning, ResNet‐152 with transfer learning exhibited the best performance, achieving recall, precision, and intersection of union of 71.98%, 77.68%, and 59.65%, respectively. The experimental results prove that the proposed method is optimal for detecting cracks in black‐box images at the pixel level.

Surface passivation is an effective way to boost the efficiency and stability of perovskite solar cells (PSCs). However, a key challenge faced by most of the passivation strategies is reducing the interface charge recombination without imposing energy barriers to charge extraction. Here, a novel multifunctional semiconducting organic ammonium cationic interface modifier inserted between the light‐harvesting perovskite film and the hole‐transporting layer is reported. It is shown that the conjugated cations can directly extract holes from perovskite efficiently, and simultaneously reduce interface non‐radiative recombination. Together with improved energy level alignment and the stabilized interface in the device, a triple‐cation mixed‐halide medium‐bandgap PSC with an excellent power conversion efficiency of 22.06% (improved from 19.94%) and suppressed ion migration and halide phase segregation, which lead to a long‐term operational stability, is demonstrated. This strategy provides a new practical method of interface engineering in PSCs toward improved efficiency and stability.

The epitaxial growth of a perovskite matrix on quantum dots (QDs) has enabled the emergence of efficient red light-emitting diodes (LEDs) because it unites efficient charge transport with strong surface passivation. However, the synthesis of wide-band gap (E g) QD-in-matrix heterostructures has so far remained elusive in the case of sky-blue LEDs. Here, we developed CsPbBr3 QD-in-perovskite matrix solids that enable high luminescent efficiency and spectral stability with an optical E g of over 2.6 eV. We screened alloy candidates that modulate the perovskite E g and allow heteroepitaxy, seeking to implement lattice-matched type-I band alignment. Specifically, we introduced a CsPb1–x Sr x Br3 matrix, in which alloying with Sr2+ increased the E g of the perovskite and minimized lattice mismatch. We then developed an approach to passivation that would overcome the hygroscopic nature of Sr2+. We found that bis(4-fluorophenyl)­phenylphosphine oxide strongly coordinates with Sr2+ and provides steric hindrance to block H2O, a finding obtained by combining molecular dynamics simulations with experimental results. The resulting QD-in-matrix solids exhibit enhanced air- and photo-stability with efficient charge transport from the matrix to the QDs. LEDs made from this material exhibit an external quantum efficiency of 13.8% and a brightness exceeding 6000 cd m–2.

Surface ligand treatment provides a promising approach for passivating defect states, improving material and device stability, manipulating interfacial energetics, and improving the performance of perovskite solar cells (PSCs). To facilitate targeted selection and design of surface ligands for PSCs, it is necessary to establish relationships between ligand structure and perovskite surface properties. Herein, surface ligands with different binding groups are investigated to determine their extent of surface coverage, whether they form a surface monolayer or penetrate the perovskite, how they influence material energetics and photoluminescence, and how this combination of factors affects PSC performance. Ultraviolet and inverse photoelectron spectroscopy measurements show that surface ligands can significantly shift the ionization energy and electron affinity. These changes in surface energetics substantially impact PSC performance, with the performance decreasing for ligands that create less favorable energy landscapes for electron transfer from MAPbI 3 to the electron transport layer, C 60 .