1D Passivated CsPbI3 Perovskite Solar Cells with High Efficiency and Stability

Inorganic black α-CsPbI₃ perovskite tends to transform into the nonperovskite δ-CsPbI₃ phase at ambient conditions, which hinders potential photovoltaic applications, such as tandem solar cells with a silicon solar cell. The β-CsPbI₃ phase has more thermodynamic stability due to the distorted PbI₆ inorganic framework compared to cubic α-CsPbI₃. We prepared the β-CsPbI₃ perovskite film by the solution method using DMAPbI₃ and CsI. We introduced a dication molecule, homopiperazium (HPI₂), into the as-prepared CsPbI₃ perovskite film to construct the 1D (HPI₂)₂PbI₆ perovkite on the surface of 3D CsPbI₃. It remarkably enhanced the stability of CsPbI₃ perovskite film through the retardation of the phase transformation from the black tetragonal β-CsPbI₃ perovskite to the yellow nonperovskite phase, δ-CsPbI₃. Moreover, the post-treatment with the HPI₂ dication provides high quality perovskite film with compact and well crystallized CsPbI₃ films through the passivation of defect sites in the CsPbI₃ perovskite. CsPbI₃((HPI₂)₂PbI₆) perovskite PSC demonstrated a champion PCE of 14.69%, while the control CsPbI₃ device without 1D (HPI₂)₂PbI₆ has only achieved about 11.53%. Moreover, 87% of the initial efficiency of the CsPbI₃((HPI₂)₂PbI₆) device was maintained under a relative humidity of 30% at room temperature.