Weakly space-confined all-inorganic perovskites for light-emitting diodes

Metal halide perovskites are promising materials for light-emitting diodes (LEDs)^1-4. Spatially confining charge carriers using nanocrystal/quantum dots^5-9, low-dimensional perovskites^10-13 and ultrathin perovskite layers¹⁴ have all been used to improve the external quantum efficiency of perovskite LEDs (PeLEDs). However, most strongly space-confined perovskites suffer from severe Auger recombination, ion migration and thermal instability, resulting in limited brightness and operational lifetime^{6,7,10-12,14-17}. Here, we report an alternative strategy based on weakly space-confined, large-grained crystals of all-inorganic perovskite. Sacrificial additives, namely, hypophosphorous acid and ammonium chloride, were used to induce nucleation and crystallization of caesium lead bromide, resulting in monocrystal grains with minimized trap density and a high photoluminescence quantum yield. Benefiting from the high carrier mobility and suppressed Auger recombination, we obtained efficient PeLEDs with an external quantum efficiency reaching 22.0%, which remained above 20% at a high current density near 1,000 mA cm^-2 and a brightness of over 1,167,000 cd m^-2. Furthermore, benefiting from the suppressed ion migration and better thermal stability, the extrapolated half-lifetime of the weakly space-confined PeLEDs increased to 185,600 h under an initial luminance of 100 cd m^-2 at room temperature. Our work is a new approach for designing efficient, bright and stable PeLEDs for real applications.