Oxidization-Free Spiro-OMeTAD Hole-Transporting Layer for Efficient CsPbI₂Br Perovskite Solar Cells

The inorganic CsPbI₂Br perovskite faces serious challenges of low phase stability and high moisture sensitivity. The moisture controllable process of a hole-transporting layer (HTL) is crucial for the development of stable and efficient inorganic perovskite solar cells (IPSCs). In this work, we proposed an oxidization-free spiro-OMeTAD hole-transport layer (HTL) with a preoxidized spiro-OMeTAD solution to prevent moisture and completely avoid the phase transition of CsPbI₂Br from the α-phase to β-phase. The oxidization-free HTL exhibited improved surface hydrophobic properties, smoother morphology, and optimized energy-level alignment compared with a traditional HTL. As a result, the CsPbI₂Br-based IPSCs achieved an efficiency of up to 14.2 and 86.6% of the initial power conversion efficiency (PCE) with 2000 h storage. Meanwhile, this oxidization-free HTL was applied in CH₃NH₃PbI₃-based PSCs and obtained 13.8% PCE enhancement, which proved the universality of the solution preoxidization tactic. We believe that the oxidization-free HTL could be an efficient strategy to replace traditional HTLs and can be widely used in perovskite solar cells, especially in moisture-sensitive PSCs.