Potassium-intercalated rubrene as a dual-functional passivation agent for high efficiency perovskite solar cells†
Defects and related trap sites are generated inevitably at grain boundaries (GBs) and on surfaces of solution-processed polycrystalline perovskite films. Seeking a suitable passivation material using facile and efficient methods to passivate the perovskite film for minimum defect density is necessary to further improve the photovoltaic performance. Here, we introduce a novel potassium-intercalated rubrene (K2Rubrene) with facile anti-solvent engineering to obtain high quality perovskite films through a novel dual-functional perovskite passivation approach. It was found that the cation–π interaction between aromatic rubrene and organic cations can immobilize the organic cations in perovskite, which can trigger heterogeneous nucleation over the perovskite precursor film to decrease the grain size and obtain a more homogeneous and uniform perovskite film. The potassium insertion in the K2Rubrene molecule, more importantly, could balance the cation–π interaction energy that occurred between the aromatic additive and the organic cations in perovskite films to reduce the barrier for better carrier transfer at GBs. Moreover, K+ could freely enter the A-site defects at the surface of the perovskite absorber and then digest the A-site shallow defects to prevent the migration and autorotation of the large organic cations at the interface between the hole transfer layer and the perovskite absorber, or perovskite/perovskite GBs. Consequently, a significant upshift of the valence band maximum and the conduction band minimum of the perovskite material leads to a more favorable energy alignment with the hole transporting material, which can enhance hole-transfer and suppress the hysteresis, and the corresponding perovskite solar cell device achieves a high efficiency of over 19%, higher than that of pristine and rubrene based devices.