Mitigating interfacial and bulk defects via chlorine modulation for HTL-free all-inorganic CsPbI₂Br carbon-based perovskite solar cells with efficiency over 14%

Hole transporting layer-free all-inorganic CsPbI₂Br carbon-based perovskite solar cells (C-PSCs) show promising prospect for photovoltaic application due to its low cost and excellent stability. However, the low power conversion efficiency (PCE) hampers its development, mainly due to the existence of defects inside the CsPbI₂Br film or at electron transporting layer (ETL)/CsPbI₂Br interface. Herein, a non-hydrophilic Cl-containing SnO₂ (SnO₂-Cl) ETL through a facile SnCl₄·5H₂O hydrolysis process is developed, which can provide fewer nucleation sites and larger nucleus spacing for the growth of high-quality CsPbI₂Br film as well as reduced ETL/CsPbI₂Br interfacial defects. Then, PbCl₂ additive is introduced into CsPbI₂Br precursor to participate in the formation of CsI-Pb[I/Br/Cl]₂-DMSO intermediate phase, which can induce more rapid and even nucleation as well as slow crystal growth before and during annealing process, bringing about the further increased crystal size and reduced defect density of CsPbI₂Br film. Based on this systematic optimization via chlorine modulation, both interfacial and bulk defects are effectively suppressed, the assembled CsPbI₂Br C-PSC achieves a champion PCE of 14.11%, which is one of the highest reported values to date.