Additive engineering is the way to handle grain boundary defects in solution processed halides perovskites semiconductor thin-films. Most of the moieties used for this role are known to be n-type small organic molecules like PCBM, BCP, amine-based compounds or insulating large Eg molecules PEO, PMMA, PS, etc. However, this is the first report we demonstrate that a commonly known p-type organic small molecule (CBP) can also passivate the defects at grain boundaries to reduce optical losses and overall improved performance of the perovskite solar cells (PSCs) in terms of efficiency and moisture/thermal stability. This work is carried out in collaboration with Physics Department (Prof. Kabra) and MEMS (Prof. Bhargava and Prof. Mallick) as a part of deliverable of NCPRE- IIT Bombay funded by MNRE-India.