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

Inorganic black α-CsPbI 3 perovskite tends to transform into the nonperovskite δ-CsPbI 3 phase at ambient conditions, which hinders potential photovoltaic applications, such as tandem solar cells with a silicon solar cell. The β-CsPbI 3 phase has more thermodynamic stability due to the distorted PbI 6 inorganic framework compared to cubic α-CsPbI 3 . We prepared the β-CsPbI 3 perovskite film by the solution method using DMAPbI 3 and CsI. We introduced a dication molecule, homopiperazium (HPI 2 ), into the as-prepared CsPbI 3 perovskite film to construct the 1D (HPI 2 ) 2 PbI 6 perovkite on the surface of 3D CsPbI 3 . It remarkably enhanced the stability of CsPbI 3 perovskite film through the retardation of the phase transformation from the black tetragonal β-CsPbI 3 perovskite to the yellow nonperovskite phase, δ-CsPbI 3 . Moreover, the post-treatment with the HPI 2 dication provides high quality perovskite film with compact and well crystallized CsPbI 3 films through the passivation of defect sites in the CsPbI 3 perovskite. CsPbI 3 ((HPI 2 ) 2 PbI 6 ) perovskite PSC demonstrated a champion PCE of 14.69%, while the control CsPbI 3 device without 1D (HPI 2 ) 2 PbI 6 has only achieved about 11.53%. Moreover, 87% of the initial efficiency of the CsPbI 3 ((HPI 2 ) 2 PbI 6 ) device was maintained under a relative humidity of 30% at room temperature.