α-Lipoic Acid Mediates Rapid Spiro-OMeTAD Doping for High-Performance Perovskite Solar Cells

The instability of 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD)-based n-i-p perovskite solar cells (PSCs) with lithium bis(trifluoromethane)sulfonimide doping arises from ionic shuttling and uncontrolled oxidation. Here, we introduce α-lipoic acid (LA) as a multifunctional additive to address these challenges. LA creates an acidic environment and accelerates the radical oxidation of spiro-OMeTAD, enabling the rapid formation of a stable hole transport layer while simultaneously precipitating excess Li⁺ ions to mitigate ion migration. Additionally, the carboxyl and disulfide groups of LA passivate interfacial defects between the perovskite and spiro-OMeTAD layers, suppressing nonradiative recombination and enhancing hole extraction. The optimized LA-doped devices achieve a power conversion efficiency (PCE) of 25.05% and show enhanced stability with a T₈₃ of 1056 h under maximum power point (MPP) tracking, far exceeding the control's PCE of 22.54% and T₈₀ of 528 h, respectively. This strategy not only streamlines the fabrication process by eliminating prolonged oxidation steps but also provides valuable insights into enhancing the operational stability of spiro-OMeTAD-based PSCs.