Metal-halide perovskite nanocrystals have demonstrated excellent optoelectronic properties for light-emitting applications. Isovalent doping with various metals (M 2+ ) 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.

Over the past few years, high external quantum efficiencies (EQE) 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, which has become increasingly important since the COVID-19 pandemic. 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 film by adding water into the precursor solution to engineer the crystallization process of spin-coated 2D perovskite. The PeLEDs deliver bright violet emission at 408 nm, with a maximum external quantum efficiency of 0.41%, a fivefold increase over control devices. This work demonstrates viable steps towards cost-effective, efficient ultraviolet PeLEDs.

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While perovskite light-emitting diodes (PeLEDs) have demonstrated external quantum efficiencies (EQEs) well over 20%, their stability limits their commercial viability. Previously, the incorporation of transition metal dopants has demonstrated improved PeLED brightness, stability, and efficiency. 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. However, while the incorporation of TFPPO dramatically increases PeLED EQE, their stability is severely compromised. 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 minutes, 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. While Mn2+ doped PeLEDs hold the potential to enable bright and efficient lighting, device stability degradation mechanisms must be further investigated.

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