Abstract: Advances in perovskite light-emitting diodes (PeLEDs) have established them as viable candidates for next-generation displays and lighting across the entire visible spectrum, with recent investigations extending their emissive properties into the deep blue and violet regions. However, achieving shorter emission wavelengths presents a significant challenge due to the larger band gaps required of both the perovskite and charge transport materials, compounding the difficulty in managing electron-hole pair recombination dynamics necessary for efficient electroluminescence. In this work, we precisely tune the halide composition in two-dimensional perovskites, successfully extending the band gap to 3.1 eV. By introducing an optimized dual-electron transport layer architecture, we improve electron injection and hole confinement within the perovskite matrix, culminating in a high-purity electroluminescent emission at 399 nm with a maximum external quantum efficiency of 0.16%, a benchmark for PeLEDs operating in this spectral domain. These findings highlight the potential of large-band-gap perovskite materials for next-generation light-emitting applications.

Standfirst: Photoresponsive perovskite light-emitting diodes can be used to build multifunctional displays that can function as touch screens, light sensors and image sensors.

Abstract: To foster equity, inclusion, and diversity within engineering departments' graduate student populations, active support of traditionally underrepresented undergraduates early in their academic journey is essential. Here, we outline the efforts of the Stanford Engineering Research Introductions Organization (SERIO) to address systemic barriers, encourage early engagement with research opportunities, and prepare early-stage underrepresented students for admission to engineering graduate programs. We highlight new pathways for institutions to foster their underrepresented undergraduate student population and facilitate their pursuit of advanced engineering education. 

Abstract: Although perovskite light-emitting diodes (PeLEDs) have demonstrated external quantum efficiencies (EQEs) well over 20%, their instability limits their commercial viability. Incorporating transition-metal dopants has previously improved the brightness, stability, and efficiency of PeLEDs. Here, we dope Mn2+ ions into a quasi-bulk 3D perovskite and introduce tris(4-fluorophenyl)phosphine oxide (TFPPO) to achieve a 14.0% peak EQE and 128,000 cd/m2 peak luminance. Whereas incorporating TFPPO into PeLEDs dramatically increases their EQE, it also severely compromises their stability. At a 5 mA/cm2 electrical current bias, PeLEDs fabricated without TFPPO (2.97% EQE) and with TFPPO (14.0% EQE) decay to half their maximum luminance in 37.0 and 2.54 min, respectively. In order to investigate this trade-off in EQE and stability, we study both photophysical and optoelectronic characteristics before and after PeLED electrical operation. Although Mn2+-doped PeLEDs hold the potential to enable bright and efficient lighting, device stability degradation mechanisms require further investigation.

Abstract: High external quantum efficiencies (EQEs) have been achieved for blue, green, red, and near-infrared perovskite light-emitting diodes (PeLEDs), and their energy efficiencies are approaching the efficiencies of III-V-based LEDs. Beyond the visible regime, ultraviolet light offers great promise for many applications such as disinfection. However, PeLEDs demonstrate poor performance in the violet/ultraviolet region, with reports of violet PeLED performance hindered by poor thin-film quality. In this work, we improve the uniformity of perovskite films by adding water into the precursor solution to engineer the crystallization process of spin-coated 2D perovskites. The resulting improved film uniformity, coupled with the reduction in nanoplate size, reduces leakage current and promotes faster recombination rates. The fabricated PeLEDs deliver bright violet emission at 408 nm with a maximum external quantum efficiency of 0.41%, a 5-fold increase over control devices. This work demonstrates viable steps toward cost-effective, efficient ultraviolet PeLEDs.

Abstract: Metal-halide perovskite nanocrystals have demonstrated excellent optoelectronic properties for light-emitting applications. Isovalent doping with various metals (M2+) can be used to tailor and enhance their light emission. Although crucial to maximize performance, an understanding of the universal working mechanism for such doping is still missing. Here, we directly compare the optical properties of nanocrystals containing the most commonly employed dopants, fabricated under identical synthesis conditions. We show for the first time unambiguously, and supported by first-principles calculations and molecular orbital theory, that element-unspecific symmetry-breaking rather than element-specific electronic effects dominate these properties under device-relevant conditions. The impact of most dopants on the perovskite electronic structure is predominantly based on local lattice periodicity breaking and resulting charge carrier localization, leading to enhanced radiative recombination, while dopant-specific hybridization effects play a secondary role. Our results suggest specific guidelines for selecting a dopant to maximize the performance of perovskite emitters in the desired optoelectronic devices.