Beyond photovoltaics, metal halide perovskites have also emerged as promising emitters for light-emitting diodes (LEDs) due to their easily tunable bandgap, narrow emission linewidth, and good charge carrier mobility.¹ Although perovskite LEDs have recently achieved rapid increase in external quantum efficiency (EQE), the emission wavelengths of these high-efficiency LEDs remains restricted to the visible and short-wavelength near-infrared regions (<920 nm).^2–5

Environmentally friendly tin iodide perovskites, particularly all-inorganic CsSnI₃, have attracted growing interest because of their intrinsic long-wavelength near-infrared emission (>920 nm), offering distinct advantages in applications such as night vision, biological tissue analysis, biomedical imaging, sensing and optical communications.^6–8 However, realizing high-efficiency CsSnI₃ based LEDs is highly challenging. Current efforts to overcome this challenge have largely focused on improving photoluminescence quantum yields, for instance, by mitigating the oxidation of Sn²⁺ and suppressing fast crystallization.^6–9 Nevertheless, the limited success in LED efficiency highlights the urgent need for a fundamentally new strategy.

Light extraction represents another critical bottleneck in perovskite LEDs due to strong optical confinement arising from the high refractive index of perovskite films.¹⁰ Discontinuous perovskite films with submicron structures can enhance light outcoupling by extracting light trapped in waveguide modes.¹¹ While this strategy has been validated in Pb-based perovskites^11,12, its application to Sn-perovskites remains rarely explored and presents distinct challenges. For CsSnI₃, light extraction is even more challenging due to its higher refractive index.^10,13 Moreover, the fast and uncontrollable crystallization in Sn-perovskites driven by the Lewis acidity of Sn²⁺ poses significant challenges in precisely tailoring their morphological features.⁶

Here we demonstrate a morphology engineering strategy that combines a low-temperature preheating step with an organic additive to precisely regulate grain and pinhole formation in CsSnI₃-based perovskite films. This microstructural control enables fine-tunable optical structures within LED stacks, substantially enhancing light outcoupling efficiency (LOE). The resulting 960 nm-emitting LEDs achieve a record-high EQE of 9.5% in the long-wavelength near-infrared region (>920 nm). Optical simulations further demonstrate that an even wider LOE range can be realized by further manipulation of grain and pinhole sizes. Our work not only offers a practical approach for precisely tailoring morphological features of tin perovskite films but also deepens the understanding of the relationship between film morphology and LED performance.