Investigation on Organic Molecule Additive for Moisture Stability and Defect Passivation via Physisorption in CH₃NH₃PbI₃ Based Perovskite

Abstract

We investigate the role of n-type organic molecule, bathocuproine (BCP), additive in perovskite semiconductor film based solar cells using first principle calculations and optoelectronic studies. A state-of-art high fill factor of 0.82 and improved open circuit voltage of 0.95 V for CH3NH3PbI3 (MAPI) based perovskite solar cells are achieved in addition with highly improved (more than one order) electroluminescence efficiency. Delayed emission spectroscopy does not show any blue shift peak or double peak emission suggests no structural changes in 3D perovskite. Contact angle studies using water droplet supports BCP is forming a capping layer to boost moisture barrier. Our experimental findings regarding no 2D structure formation has also been supported by first-principles electronic structure calculations based on DFT in MAPI after insertion of BCP. Furthermore, calculations suggest that a physisorption type of interaction has been found in between MAPI and BCP with an average distance of 2.9 Å. These results were found to be in agreement with steady-state and transient photoluminescence studies where an improved PL is observed by using perovskite solution with BCP additive. Chemical analysis and electroluminescence study confirmed the reduction in defect sites by BCP addition. The study suggests that BCP being a small molecule plays an important role in passivating and improving the MAPI film quality and points to an approach toward utilizing other such additives. Furthermore, this approach can be useful for other optoelectronic devices too based on wider bandgap perovskite semiconductors.