Unraveling the impact of graphene nanostructures passivation on the electrical properties of the perovskite solar cell

Herein, the impact of graphene nanoplatelets (GNPs) passivation on the performance of perovskites solar cells (PSCs) has been investigated using fluorescence spectroscopy, electrochemical impedance spectroscopy (EIS), and temperature dependence capacitance vs. frequency (C-f-T) measurements. Devices passivated with GNPs exhibited improved performance compared to the un-passivated device. The photoluminescence (PL) intensity of passivated perovskites films amplified as compared to the un-passivated perovskites film. The PL lifetime associated with the bulk of the perovskite increased from 830 ps to 991 ps, and the lifetime corresponds to the surface recombination delayed from 30 ns to 38 ns, confirming the suppression of non-radiative recombination centers on perovskites surface. The EIS measurements reveal that the passivated devices have higher recombination resistance and lower charge transport resistance, further confirming the decrease of recombination losses and improvement in the charge transport across the perovskites/charge selective contact (CSC) interface. Moreover, the temperature-dependent EIS measurement shows that the charge carrier lifetime increased from 30 mu s in the un-passivated device to 42 mu s in the passivated device, whereas the activation energy reduced from 43 meV to 13 meV. The C-f-T spectra reveal that the low-frequency evolution of capacitance in passivated devices decreases indicating the decrease of charge accumulation at perovskites/CSC interface. Finally, the activation energy for the charging/discharging of trap states in passivated devices dropped to 89 meV compared to 104 meV in the un-passivated device, further confirming the decrease in interfacial trap depth via GNPs passivation.