The trade-off between high luminance and moisture robustness of inorganic metal halide perovskite light-emitting electrochemical cells (PeLECs) is necessary for their use under harsh environmental conditions. Herein we report a new approach to improve the properties of a poly(ethylene oxide) (PEO)–CsPbBr₃ perovskite device with a transparent single-walled carbon nanotube electrode consisting of two-layered cell encapsulation and 50 or 80% relative humidity stress-aging. The encapsulation into metal catalyst-free cross-linked polymethylhydrosiloxane (PMHS) does not impose a negative influence on the perovskite material's optoelectronic properties. Furthermore, the PeLECs are coated with a polydimethylsiloxane Sylgard 184 (PDMS) capping layer to provide mechanical strength. After 168 hours of accelerated aging at 80% relative humidity, the double-layer (PMHS/PDMS) encapsulated PeLEC indicates a luminance of >2000 cd m⁻² at 4 V demonstrating the highest current efficiency and photoluminescence quantum yield among all samples (including non-aged and non-encapsulated ones) while the luminescent properties of a double-encapsulated PeLEC degrade significantly in a nitrogen atmosphere and at 50% relative humidity. Thereby, we show the optimal encapsulation recipe for a high-humidity environment that allows not only the use of PeLECs under extremely high relative humidity conditions but also improves their performance due to water diffusion. X-Ray diffraction data reveal that pronounced 〈hh0〉 and 〈00l〉 texture appears in single and doubled encapsulated thin films after 80% water vapor treatment. In contrast, the reference (non-encapsulated) perovskite film does not show complete texture formation, demonstrating possible grain coarsening and crystal quality deterioration after 80% water vapor treatment. The proposed approach combining PMHS/PDMS encapsulation and aging reveals a new promising strategy to develop efficient perovskite devices operating at high humidity, which also can be made flexible or even stretchable.