One Stone, Three Birds: Multifunctional SnSO Oxidant for Efficient Perovskite Solar Cells

Perovskite solar cells (PSCs) that incorporate a two-dimensional/three-dimensional (2D/3D) perovskite layer demonstrate enhanced stability compared to that of their purely three-dimensional counterparts. This improved stability can be attributed to the superior chemical stability of the 2D perovskite layer. However, the poor electrical properties of the 2D perovskite layer also limit further improvement of device performance. Moreover, as the most effective hole transport layer (HTL) in 2D/3D PSCs, lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI)-doped 2,2 ',7,7 '-tetrakis(N,N-di(4-methoxyphenyl)amino)-9,9-spirobifluorene (spiro-OMeTAD) usually needs prolonged exposure to air to improve its conductivity, which to some extent increases the risk of water/oxygen infiltrating into the perovskite layer, leading to the degradation of the perovskite active layer. Herein, we developed a multifunctional dopant, tin oxysulfide (SnSO) in the spiro-OMeTAD layer to improve the efficiency and stability simultaneously. On one hand, SnSO accelerates the oxidation of the spiro-OMeTAD film and significantly improves its conductivity. On the other hand, strong interaction among the SnSO with 2D perovskite makes up for the poor conductivity of 2D perovskite and passivates perovskite defects, which also creates an interface built-in electric field to improve hole transport efficiency and reduce charge recombination at the 2D/HTL interface. Furthermore, the doping of SnSO makes the energy level arrangement at the 2D/3D interface more favorable for carrier transfer. Finally, after optimizing the doping concentration of SnSO, the target device achieved a high photoelectric conversion efficiency (PCE) of 24.5%. Simultaneously, the device's stability increased dramatically under various testing conditions.