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.