One of the important factors in the performance of perovskite solar cells (PSCs) is effective defect passivation. Dimensional engineering technique is a promising method to efficiently passivate non-radiative recombination pathways in the bulk and surface of PSCs. Herein, a passivation approach for the perovskite/hole transport layer interface is presented, using a mixture of guanidinium and n-octylammonium cations introduced via GuaBr and n-OABr. The dual-cation passivation layer can provide an open-circuit voltage of 1.21 V with a power conversion efficiency of 23.13%, which is superior to their single cation counterparts. The mixed-cation passivation layer forms a 1D/2D perovskite film on top of 3D perovskite, leading to a more hydrophobic and smoother surface than the uncoated film. A smooth surface can diminish non-radiative recombination and enhance charge extraction at the interface making a better contact with the transport layer, resulting in improved short-circuit current. In addition, space charge-limited current measurements show a three times reduction in the trap-filled limit voltage in the mixed-cation passivated sample compared with unpassivated cells, indicating fewer trapped states. The shelf-life stability test in ambient atmosphere with 60% relative humidity as well as light-soaking stability reveal the highest stability for the dual-cation surface passivation.
- surface passivation