Flocculating‐Regulated TiO₂ Deposition Enables the Synergistic Effect of Doping for Perovskite Solar Cells with Efficiency Exceeding 25.8%

Abstract The planar perovskite solar cells (PSCs) using TiO 2 as the electron transport layer (ETL) are undergoing a stagnated efficiency improvement, which the inferior TiO 2 ETL mainly limits. Herein, a flocculating‐regulated TiO 2 deposition using SnCl 2 ·2H 2 O is reported as the flocculate to control the nanoparticle size finely for optimizing TiO 2 deposition and to achieve a synergistic Sn doping. The SnCl 2 ·2H 2 O incorporated into bath precursor can bridge‐link the suspended nanoparticles, which promotes the precipitation of large‐sized nanoparticles and leaves the smaller‐sized nanoparticles for deposition, leading to a compact TiO 2 film with marked reduced surface roughness. Meanwhile, along with flocculating‐regulated TiO 2 deposition, it can also be achieved the Sn‐doping of TiO 2 , which increases the conductivity of TiO 2 thin films by ≈2.5 times. As a consequence, attributing to the optimized interface contact and accelerated interfacial electron transport, the planar PSCs achieved a certification efficiency of 25.85%, the highest value among the TiO 2 ‐based planar PSCs to date. In addition, the PSCs can maintain 99% of their initial efficiency after more than 4500 h of storage in ambient air, showing excellent stability.