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.