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

The planar perovskite solar cells (PSCs) using TiO2 as the electron transport layer (ETL) are undergoing a stagnated efficiency improvement, which the inferior TiO2 ETL mainly limits. Herein, a flocculating‐regulated TiO2 deposition using SnCl2·2H2O is reported as the flocculate to control the nanoparticle size finely for optimizing TiO2 deposition and to achieve a synergistic Sn doping. The SnCl2·2H2O 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 TiO2 film with marked reduced surface roughness. Meanwhile, along with flocculating‐regulated TiO2 deposition, it can also be achieved the Sn‐doping of TiO2, which increases the conductivity of TiO2 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 TiO2‐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. [ABSTRACT FROM AUTHOR]