Bismuth is considered as one of the most promising candidates to replace Pb in the organo-lead halide perovskite, a classical material for various optoelectronic applications. When utilized in a photovoltaic cell, the performance of the cell drops due to deterioration in the absorber film and the changes in its crystal structures. In this work, a small amount of dodecylammonium chloride, C12H25NH3Cl (DCl) is added into Cs3Bi2I9 (CBI), resulting in a pinhole-free high-quality perovskite (PVK) film via a single-step solution processability, also confirmed by FTIR and XPS analyses. Structural, optical, and microscopic analyses showed that the quality, surface features, and crystallinity of the CBI films are significantly improved by adding DCl. The prepared films are successfully demonstrated in a solar cell and exhibited considerably improved photovoltaic (PV) characteristics (VOC by ~47%, JSC by ~33%, FF by 13%, and PCE by 115%) over pure CBI-based devices. Moreover, the PV device retained more than 95% of its initial PCE in the ambient laboratory environment (relative humidity 55±5%). To the best of our knowledge, this is the highest PCE along with extended environmental stability reported for solution processed CBI-based perovskite solar cells.