Owing to their high efficiency and extended environmental stability, hybrid 2D/3D-perovskites (HPVKs) are gaining an increasing interest in the field of organometal halide perovskite solar cells (PSCs). In HPVKs, the 3D component acts as an active material, where its 2D-counterpart provides protection against environmental factors. Here in, we add dodecylammonium-chloride (DACl into the precursor solution of 3D-perovskites (FAMAPbI(3)) to achieve HPVKs. The formation of HPVK is confirmed by XRD, optical absorption, and Fourier-transform infrared (FTIR) spectroscopies. The structural and optical analysis affirmed that in the case of HPVKs, not only the crystallinity of perovskites is improved significantly but also a variation in its structural properties and optical bandgap have occurred. It is also observed that the surface morphologies of HPVK films are considerably improved with the incorporation of DACl. A minute amount of CsI is also added into the precursor solution of HPVKs, which further assist the formation of HPVKs and consequently causes a significant increase in the carrier lifetime. Finally, a solar cell made of HPVKs shows an improved PCE than pure 3D-perovskites. All HPVKs films and solar-cells are prepared in the ambient humidity and found to be more hydrophobic and stable, not only under relative humidity > 50% but also under high thermal stress of 85 degrees C.