Low‐Temperature TiO2 Electron Transporting Layer for Planar Hole Transport Material‐Free Carbon Electrode‐CsFA‐Based Perovskite Solar Cells

Carbon electrode‐based perovskite solar cells (C‐PSCs) without a hole transport material (HTM) are cost‐effective and exhibit impressive long‐term stability. The electron transporting layer (ETL) plays a crucial role in planar CsFA‐based HTM‐free C‐PSCs, serving as both an electron transporter and a hole barrier. Herein, the role of low‐TiO2 morphology and thickness on the performance of CsFA‐based HTM‐free C‐PSCs are addressed. Herein, the devices are fabricated with a simple structure fluorine‐doped tin oxide /TiO2 nanoparticles (TiO2 NPs)/Cs0.17FA0.83Pb(I0.83Br0.17)3/carbon, using low‐temperature processes (≤150 °C) under ambient air conditions. By optimizing TiO2 NP layer thickness via spin‐coating speed adjustments, the ETL's coverage and compactness are improved, enhancing the perovskite film's quality, crystallinity, and grain size. An optimal TiO2 ETL at 1500 rpm yields 10.80% efficiency and demonstrates exceptional stability, maintaining 80% efficiency over 120 days in an air environment without encapsulation. The enhancement in device performance is attributed to improved surface properties of the TiO2 NPs ETL, effectively reducing interfacial charge recombination. This straightforwardly supports the development of sustainable, commercial‐ready CsFA HTM‐free C‐PSCs.