Abstract A common approach to enhance the stability of metal halide perovskites (MHPs) implemented in optical and optoelectronic devices is to incorporate polymer additives into the perovskite layer. A β ‐(1,4) cellulose oligosaccharide (COS) synthesized by mechanocatalytic depolymerization of cellulose has been incorporated to films of the BA 2 MA 4 Pb 5 I 16 (BA = n ‐butylammonium and MA = methylammonium) two‐dimensional (2D) Ruddlesden‐Popper (RP) hybrid perovskite. Scanning Electron Microscopy (SEM) images displayed a three‐fold reduction of the 2D RP perovskite grains (≈30–40 nm), close to the quantum confinement scale. The analysis of the dark J–V curves of single carrier devices by using the space charge limited current (SCLC) method resulted in a rise of the defect concentration. A notable 14‐fold increase in the photoluminescence (PL) signal at high COS content is detected. Moreover, the analysis of the temperature dependence PL measurements (80–300 K) resulted in a larger exciton binding energy, Eb = 180 to 370 meV, at high COS content. Light emitting diodes of the 2D RP perovskites (PeLEDs) are fabricated w/o the COS compound. The stability test performed under operation (5 V) displays 20 times higher operational lifetimes at high COS content while the luminance is also increased in the devices with the COS compound.