Additive engineering of 4, 4′-Bis (N-carbazolyl)-1, 1′-biphenyl (CBP) molecules for defects passivation and moisture stability of hybrid perovskite layer

Abstract

Halide perovskites are known to have grain boundary defects and there are continuous efforts in the community to overcome them by various passivation techniques, like the use of various small organic molecules as additives, solvent additives, mixing of larger cations to decorate the grain boundaries at interfaces with quasi-2D perovskites. This paper reports an additive-engineering strategy which provides moisture resistance and passivates defects of CH3NH3PbI3 (MAPbI3) absorber layer of perovskite thin film via introducing organic molecule 4, 4′-Bis (N-carbazolyl)-1,1′-biphenyl (CBP). GIXRD results show that CBP molecules do not enter into the perovskite crystal. Contact angle measurement and XPS studies suggest that CBP plays a role in boosting moisture resistance. XPS also supports that a small amount of CBP reduces carbon related impurities. CBP causes improved optical properties via bulk defect passivation. These results are found to be in accordance with steady-state and transient photoluminescence studies, where improved photoluminescence is observed for CBP added MAPbI3 films with reduced non-radiative recombination centers. Defects passivation and moisture resistance imparted by CBP molecules result in improved photovoltaic parameters and electroluminescence efficiency eventually. The study leads to a rational approach towards choosing other additives of appropriate molecular size for enhancing perovskite solar cell performance.