Dopant-Free Ultra-Thin Spiro-OMeTAD Enables Near 30%-Efficient n–i–p Perovskite/Silicon Tandem Solar Cells

A major challenge for n-i-p structured perovskite/silicon tandem solar cells (TSCs) is the use of 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD), a commonly used hole transport layer, which induces significant optical losses and consequently reduces device current. Herein, we propose an ultra-thin (10 nm) vacuum thermal evaporation (VTE)-deposited spiro-OMeTAD, coupled with a 2D/3D perovskite heterojunction, to simultaneously enhance the optical and electrical properties of n-i-p perovskite/silicon TSCs. Our results demonstrate that the 10-nm-thick spiro-OMeTAD layer significantly improves optical performance, achieving a 92.2% reduction in parasitic absorption and an 18.4% decrease in reflection losses. Additionally, the incorporation of the 2D/3D perovskite heterojunction facilitates improved molecular arrangement and enhanced surface uniformity of the ultrathin spiro-OMeTAD, leading to higher tolerance to interface defects and more efficient hole extraction. Consequently, n-i-p perovskite/silicon TSCs featuring ultrathin spiro-OMeTAD exhibit remarkable efficiencies of 29.73% (0.135 cm²) and 28.77% (28.25% certified efficiency, 1.012 cm²), along with improved stability.