Spiro-Phenothiazine Hole-Transporting Materials: Unlocking Stability and Scalability in Perovskite Solar Cells

Improving both the efficiency and long-term stability of perovskite solar cells (PSCs) is critical for their commercial deployment. Despite the widespread use of spiro-OMeTAD as a hole-transporting material (HTM), its inhomogeneous doping behavior and susceptibility to moisture and heat have hindered its large-scale industrial implementation. Here, a family of spiro-phenothiazine-based HTMs (PTZ) is reported to address these drawbacks. Among them, the fluorene derivative (PTZ-Fl) shows a larger Li⁺ affinity and forms a compact interphase by intercalation in the perovskite passivating layer that prevents Li⁺ migration. PSCs incorporating PTZ-Fl exhibit power conversion efficiencies (PCEs) up to 25.8% (certified 25.2% under reverse scan), retaining 80% of their initial performance after 1000 h under ISOS-L-3 protocol. Furthermore, a 5 × 5 cm mini-module reaches a PCE of 22.1%, surpassing spiro-OMeTAD-based PSCs and retaining over 85% of its efficiency after 1100 h under ISOS-D-1 protocol. These results demonstrate that PTZ-Fl not only enables high PCEs but also substantially improves operational stability, offering a promising pathway toward the large-scale deployment of next-generation PSCs.