Perovskite solar cells have gained a lot of attention in the recent years due to their high potential in power conversion efficiency (PCE) and low production cost. Despite these advantages, they are still not commercialized, mainly because of their low stability. In this paper, we seek to achieve better efficiency and stability by composition and surface engineering of the perovskite layer. Surface engineering is done using passivating agents with the aim to passivate deep trapped states on the perovskite and ETM interface. Using the TRPL technique we found 4 potential molecules for passivating agent, namely Titanium tetrabromide, Tetrabutylammonium Bromide, 1,4-Dimethyl-4H-1,2,4-Triazolium Iodide, and 4-Fluorophenethylammonium. These molecules can have a positive effect on recombination rate in the perovskite layer and result in an improvement in the power conversion efficiency of a device. For better stability, we deviated from the mostly-studied perovskite formula of MAPbI3 and tested a cesium doped formula (Cs0.1FA0.9PbI3). XRD of the new formula showed very stable α phase perovskite even after 4 days of exposure to the outside environment and the device made with the new formula gave a PCE of 19.45%.