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There is growing demand for convenient and cost-efficient ethanol sensing techniques in daily life and industry. However, the complexity, high cost, and large volume of the equipment hinder the widespread use of conventional ethanol sensing techniques. Here, we introduce a test paperlike visualized label-free ethanol sensing platform by taking advantage of the instability of 2D Ruddlesden-Popper perovskite in ethanol. The photoluminescence of PEA2Csn-1PbnBr3n+1 2D perovskite changes from deep blue to green distinctly when exposed to ethanol. A cheap demo ethanol test paper is fabricated by this 2D perovskite and paper using a simple method, demonstrating interesting rapid and convenient ethanol sensing performance. Crystal analysis, constituent analysis, spectral analysis, and molecular dynamic (MD) simulation reveal the crystal structure transformation from 2D to 3D induced by the migration of PEA+ cations in the original 2D perovskite when exposed to ethanol. In addition, a chemiresistive sensor based on the 2D perovskite and on the 2D-3D phase transformation is developed and demonstrates a high ethanol detection sensitivity with a limit down to 0.7 ppm. The photodetector fabricated by the 2D perovskite also demonstrates tunable sensitivity upon the controllable 2D-3D transformation. This remarkable colorimetric, chemiresistive, and photosensitive perovskite is expected to highlight its future application and be a supplement to the existing ethanol sensing and photodetector techniques.

The successful implementation of perovskite light-emitting diodes (PeLEDs) in advanced displays and lighting has proven to be challenging because of the inferior performance of blue devices. Here, we point out that a strained system would lead to the quasi-degenerate energy state to enhance the excited-state transition due to the formation of double-polarized transition channel. The tensile strained structure also brings about a synergetic control of the carrier dynamics in virtue of lattice structure deformation and reduced dimensional phase regulation to promote carrier population in large bandgap domains and to realize near-unit energy transfer from the large bandgap phases to the emitter phases. Accordingly, high external quantum efficiencies of 14.71 and 10.11% are achieved for the 488- and 483-nanometer PeLEDs. This work represents a versatile strategy using a strained system to achieve enhanced radiative emission for the development of efficient PeLEDs.

Wide bandgap inorganic perovskites have attracted intensive attention owing to their potential applications in high-efficiency tandem solar cells and indoor photovoltaics. However, the performance of wide bandgap inorganic perovskite solar cells (PSCs) suffers from large energy loss due to a high degree of atom (or lattice) disorder and trap defects induced by phase transformation. Herein, the defect states of 1.82 eV inorganic CsPbI3−xBrx perovskite are investigated by thermal admittance spectroscopy, photoluminescence spectroscopy, transient photovoltage, and space-charge-limited current measurement. It is found that the deep-level interstitial defects with an activation energy of 321 meV can be reduced by two orders of magnitude under prolonged storage under low-humidity ambient conditions. Admittance spectroscopy in the low-frequency region also reveals the evolution of activation energy for ion migration. The self-healing process, which is assisted by the ion migration, is proposed to explain the mitigation of the deep-level interstitial defects. Device characterization and drift-diffusion model-based simulation further elucidate the reduction of nonradiative Shockley-Read-Hall recombination and the enhancement of carrier extraction, both attributed to the mitigation of the trap defects. This work highlights the critical roles of the self-healing process in diminishing the deep-level interstitial defects for high-performance inorganic perovskite optoelectronics. © 2022 The Royal Society of Chemistry.

Halide perovskite light-emitting diodes (PLEDs) have raised considerable attention due to their high color purity and rapid development performance. Although high-efficiency PLEDs have been continuously and repeatedly reported, the lack of a highly reproducible manufacturing process for PLEDs hinders their future development and commercialization. Here, a generic protocol for rational control of the nucleation and crystallization process of the perovskite emission layer is reported. Through the monitoring of the photoluminescence during spin-coating, the antisolvent dripping time can be precisely determined. Therefore, it is possible to repeatedly produce a perovskite emission layer with high PLQY, smooth surface/interface, and good homogeneity. As a result, high-performance PLEDs are easily obtained. Moreover, the standard deviation of the fabricated PLEDs performance is smaller than 0.8%, showing high reproducibility independent of the process conditions such as the process temperature, solvent atmosphere, and spin-coating parameters, which highlights the statement of the importance of rationally control of the antisolvent process. The methodology provides important progress towards highly reproducible manufacturing of PLEDs for practical applications. © 2021 Wiley-VCH GmbH

The efficiency of blue perovskite light-emitting diodes (PeLEDs) is lagging far behind their green and red counterparts. Here, we demonstrate high-efficiency sky-blue PeLEDs by employing pseudohalide thiocyanates, which are ammonium thiocyanate (NH4SCN), methylammonium thiocyanate (MASCN), and guanidine thiocyanate (GASCN), as additives in a quasi-two-dimensional cesium lead halide perovskite emission layer. Although the thiocyanate incorporation can modify the formation energy to induce more n = 1 phases that are undesirable for light emission due to their strong electron-phonon coupling, the pseudohalide additive is able to passivate the nonradiative trap defects and stabilize the perovskite structure by filling the halide vacancy, coordinating to Pb with the Pb-S bond, and enhancing the bonding of the perovskite lattice. It is found that the passivation effect outperforms the electron-phonon coupling loss, yielding a higher photoluminescence quantum yield. As a result, the external quantum efficiencies of the sky-blue PeLEDs are improved from 5.75 to 11.93%. The thiocyanate-modulated devices also exhibit good spectral and operational stability. This work revealed the important roles of the pseudohalide thiocyanates in the improvement of sky-blue PeLEDs.