<p>Spin light-emitting diodes are promising for applications in next-generation optoelectronics, spin photonics and communication devices. However, rapid spin relaxation at room temperature causes early loss of spin polarization, constraining the asymmetric electroluminescence brightness (<i>B</i>_CP-EL, the product of the electroluminescence dissymmetry factor and luminance) to suboptimal levels of 10–1,000 cd m⁻². Here we realize a hybrid chiral perovskite heterostructure that features distributed achiral emitters spatially separated by a wide-bandgap chiral spin injector, enabling modulation of the effective contribution of exciton–exciton interactions to spin relaxation. The hybrid chiral perovskite suppresses the rapid rise of the spin-flip rate with excitation density and extends the spin-relaxation time to the nanosecond regime while preserving a photoluminescence quantum efficiency of 78%. The resulting spin light-emitting diodes deliver a <i>B</i>_CP-EL of 13,084 cd m⁻², a maximum electroluminescence dissymmetry factor of 0.2 and an extrapolated half-lifetime that exceeds 5,000 h at an initial luminance of 100 cd m⁻². Kinetic analysis further reveals a crossover in the dominant determinant of emission polarization, from initial spin polarization at low excitation to spin-flip rate at high excitation. These findings provide mechanistic insights into spin dynamics, opening up opportunities for next-generation displays and quantum technologies.</p>