1D-phase-induced porous templates for efficient two-step-processed mixed-halide perovskite solar cells

The two-step deposition method for preparing mixed-halide perovskite films is advantageous over the common one-step antisolvent method due to its higher controllability and repeatability. However, a key challenge in the two-step process is to create a porous lead-halide template, which promotes the complete conversion into mixed-halide perovskite thin film. Herein, we propose a dimensional engineering strategy to achieve porous lead-halide templates by introducing N,N-diisopropylbenzimidazolium bis(trifluoromethanesulfonyl)imide (IPR-TFSI) in the first step of template formation. First, the IPR⁺ cation induces the preferential growth of 1D phase perovskites, causing more voids in lead halide. Second, the TFSI^- anion passivates the uncoordinated Pb²⁺ defects and reduce the non-radiative recombination loss in the mixed-halide perovskite thin film. As a result, the mixed-halide perovskite solar cells with a bandgap of 1.65 eV achieve a power conversion efficiency (PCE) up to 21.38 %. Additionally, these solar cells have shown improved thermal stability, retaining over 85 % of their initial PCE after being continuously heated at 85 °C for 1000 h.