Dual-function ammonium salt as a lithium-free dopant and passivator for efficient and stable perovskite solar cells

Lithium salt-based hole transport layer (HTL) dopants commonly used in perovskite solar cells (PSCs) are known to negatively impact stability due to their intrinsic hygroscopic properties and ion migration. In this study, we introduce an ammonium salt, p-methoxyphenylethylamine bis(trifluoromethyl)sulfonimide (MPT), as a novel dual-function dopant for the HTL in PSCs. The chemical interaction between MPT and the widely used HTL material spiro-OMeTAD generates high concentrations of spiro-OMeTAD⁺ radicals, effectively enhancing the doping of spiro-OMeTAD. Additionally, MPT reacts with the perovskite layer, forming a 2D perovskite structure at the perovskite/HTL interface, which passivates defects and suppresses interfacial ion migration. As a result, PSCs with MPT doping achieved a remarkable power conversion efficiency (PCE) of 25.52% for small-area devices (0.045 cm²) and 21.01% for mini-modules (16.8 cm²). Moreover, the incorporation of MPT significantly enhances the moisture, light, and thermal stability of the PSCs by eliminating Li⁺ and suppressing I⁻ migration. Notably, PSCs with MPT-doped PTAA retained 84% of their initial PCE after 1,300 h of aging at 60 °C in a nitrogen-filled glovebox. Our work presents a unique doping strategy for the HTL in PSCs, offering a promising approach to simultaneously improve both the stability and efficiency of these devices.