Boosting Spiro‐OMeTAD Doping via Structurally Asymmetrical Nanohorns for High‐Performance Carbon‐Based Perovskite Solar Cells

Abstract The doping level of 2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene (Spiro‐OMeTAD), a commonly used hole transport layer in perovskite solar cells (PSCs), is crucial for its electrical conductivity and the final photovoltaic performance. The routine oxygen‐oxidation doping strategy falls short in achieving high‐level doping due to the sparsity and random distribution of dopants within the solid Spiro‐OMeTAD film. Here the use of carbon nanohorns (CNH) as a promoter to significantly enhance the doping level of Spiro‐OMeTAD is reported. The unique asymmetry and polar structure of CNH not only enable effective charge transfer between CNH and Spiro‐OMeTAD, also exhibit confinement effect to trap Li⁺ ions and O₂, promoting the consecutive chemical doping processes. Corresponding carbon‐based PSCs achieved a power conversion efficiency of 23.24% (22.51% certified), and demonstrated exceptional long‐term durability, retaining 95.3% of the initial PCE (power conversion efficiency) after 1500 h of tracking at maximum power point (MPP) under 100 mW cm⁻² illumination.