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Modifying Mesoporous TiO2 by Ammonium Sulfonate Boosts Performance of Perovskite Solar Cells.

Mesoporous-structure perovskite solar cells (meso-PVKSCs) have been widely utilizeddue to the achieved high efficiency, for which the TiO2 layer usually suffers from sufficient electron trap states, low electron mobility and inavoidable catalytic activity. Herein, mesoporous TiO2 (m-TiO2) layer is modified by tetraethylammonium p-toluenesulfonate (abbreviated as TEATS) for the first time, leading to a significant photoelectric conversion efficiencies (PCE) enhancement from 19.14% to 20.69% for Cs0.05MA0.12FA0.83PbI2.55Br0.45 (abbreviated as CsMAFA) meso-PVKSC. In particular, the obtained champion open circuit voltage (Voc) is 1.18 V, which is a record high value for meso-PVKSCs with CsMAFA triple cation mixed perovskite. A series of measurements were employed to investigate the influences of TEATS modification on the energy band structures of TiO2 as well as the CsMAFA perovskite layer atop, unveiling that TEATS modification benefits defect passivation of TiO2 film along with decrease of the work function of TiO2. Besides, TEATS modification helps to improve the wettability of perovskite precursors on m-TiO2 substrate, affording improved film quality of perovskite with enhanced crystallinity and grain size. Consequently, the trap states existed in perovskite film can be passivated and the interfacial charge recombination is suppressed. This further benefits the improvement of the ambient stability of devices.