Semi-transparent metal electrode-free all-inorganic perovskite solar cells using floating-catalyst-synthesized carbon nanotubes

Perovskite solar cells offer a promising future for next-generation photovoltaics owing to numerous advantages such as high efficiency and ease of processing. However, two significant challenges, air stability, and manufacturing costs, hamper their commercialization. This study proposes a solution to these issues by introducing a floating catalyst-based carbon nanotube (CNT) electrode into all-inorganic perovskite solar cells for the first time. The use of CNT eliminates the need for metal electrodes, which are primarily responsible for high fabrication costs and device instability. The nanohybrid film formed by combining hydrophobic CNT with polymeric hole-transporting materials acted as an efficient charge collector and provided moisture protection. Remarkably, the metal-electrode-free CNT-based all-inorganic perovskite solar cells demonstrated outstanding stability, maintaining their efficiency for over 4000 h without encapsulation in air. These cells achieved a retention efficiency of 13.8%, which is notable for all-inorganic perovskites, and they also exhibit high transparency in both the visible and infrared regions. The obtained efficiency was the highest for semi-transparent all-inorganic perovskite solar cells. Building on this, a four-terminal tandem device using a low-band perovskite solar cell achieved a power conversion efficiency of 21.1%. These CNT electrodes set new benchmarks for the potential of perovskite solar cells with groundbreaking device stability and tandem applicability, demonstrating a step toward industrial applications.