Low‐Temperature Remote Plasma Synthesis of Highly Porous TiO ₂ as Electron Transport Layers in Perovskite Solar Cells

Abstract Halide perovskite solar cells (PSCs) offer high efficiency at low production costs, making them a promising solution for future photovoltaic technologies. Optimizing charge transport layers is crucial, with porous TiO ₂ widely used as electron transport layers (ETLs) due to their suitable energy band alignment, transparency, and abundance. However, their performance depends strongly on crystallinity, requiring high‐temperature processing (>450 °C), which increases costs and limits their applicability on flexible substrates. Low‐temperature wet‐chemical methods face scalability issues due to material waste and hazardous solvents. Therefore, plasma‐based technologies provide a scalable, eco‐friendly alternative for fabricating oxide‐based ETLs. This study presents a plasma‐based synthesis of TiO ₂ layers using remote plasma‐assisted vacuum deposition (RPAVD) and soft plasma etching (SPE) at temperatures below 200 °C, enabling precise control over microstructure and porosity. The resulting nanocolumnar and aerogel‐like TiO ₂ films are antireflective and enhance optical and electronic properties, leading to improved PSC efficiency (champion PCE = 14.6%) comparable to high‐temperature processed devices. The devices are based on a 3D organometal perovskite with mixed cations (MA, FA, Cs, Rb) and halides (I, Br), with a nominal composition of (Rb _0.03 Cs _0.03 FA _0.69 MA _0.25 )(PbI ₃ ) _0.83 (PbBr ₃ ) _0.17 . Our results highlight the potential of RPAVD+SPE for producing low‐temperature ETLs, offering a feasible, industrially scalable solution for flexible, high‐performance photovoltaics.