Degradation of Two-Dimensional CH₃NH₃PbI₃ Perovskite and CH₃NH₃PbI₃/Graphene Heterostructure

Hybrid organic–inorganic metal halide perovskites have been considered as promising materials for boosting the performance of photovoltaics and optoelectronics. Reduced-dimensional condiments and tunable properties render two-dimensional (2D) perovskite as novel building blocks for constructing micro-/nanoscale devices in high-performance optoelectronic applications. However, the stability is still one major obstacle for long-term practical use. Herein, we provide microscale insights into the degradation kinetics of 2D CH₃NH₃PbI₃ (MAPbI₃) perovskite and CH₃NH₃PbI₃/graphene heterostructures. It is found that the degradation is mainly caused by cation evaporation, which consequently affects the microstructure, light–matter interaction, and the photoluminescence quantum yield efficiency of the 2D perovskite. Interestingly, the encapsulation of perovskite by monolayer graphene can largely preserve the structure of the perovskite nanosheet and maintain reasonable optical properties upon exposure to high temperature and humidity. The heterostructure consisting of perovskite and another 2D impermeable material affords new possibilities to construct high-performance and stable perovskite-based optoelectronic devices

Light Extraction of Trapped Optical Modes in Polymer Light-Emitting Diodes with Nanoimprinted Double-Pattern Gratings

Despite the rapid development of polymer light-emitting diodes (PLEDs), the overall device efficiency is still limited because ∼80% of the generated light is trapped in a conventional device architecture by the high refractive index of organic materials and the optical confinement and internal reflection. The implementation of the energy dissipation compensation techniques is urgently required for further enhancement in the efficiency of PLEDs. Here, we demonstrate that incorporating the double-pattern Bragg gratings in the organic layers with soft nanoimprinting lithography can dramatically enhance the light extraction of trapped optical modes in PLEDs. The resulting efficiency is 1.35 times that of a conventional device with a flat architecture used as a comparison. The experimental and theoretical analyses indicate that the enhanced out-coupling efficiency is attributed to the combination of the ordinary Bragg scattering, the guided-mode resonance (GMR), surface plasmon polariton (SPP) modes, and the hybrid anticross coupling between GMR and SPP, leading to the extraordinary efficient photo flux that can transfer in direction of the leaky modes. We anticipate that our method provides a new pathway for precisely manipulating nanoscale optical fields and could enable the integration of different optical modes in PLEDs for the viable applications