In present study, I report the synthesis of PbSe nanocrystal quantum dots (NQDs) and its solar cell application. PbSe NQD is known for promising material of $3^{rd}$ generation solar cells. I successfully fabricated PbSe NQDs heterojunction solar cell using Layer-by-Layer (LBL) spin coating. I exchanged the bulky surface ligand of PbSe NQDs such as oleic acid (OA) to EDT, then I could achieve strong electronic coupling of PbSe NQDs. By optimizing solar cell fabrication condition, I could increase the overall performance of PbSe NQDs solar cell. Finally, I achieved PbSe NQDs heterojunction solar cell exceeding photocurrent of $20 mA/cm^{2}$. Additionally, I improved PbSe NQD stability by surface treatment with ammonium chloride (NH4Cl). Absorption and PL spectroscopy results revealed that our stability improved PbSe NQDs can maintain their original optical properties over 1 week. Stability improved PbSe NQDs can be applied to PbSe heterojunction solar cell with ultra-long life time in the future.