Dopant-free Spiro-OMeTAD as hole transporting layer for stable and efficient perovskite solar cells

High efficiency organic-inorganic hybrid perovskite solar cells have attracted significant attention and experienced a rapid development in recent years. Lithium-doped spiro-OMeTAD is one of the most commonly used hole transporting material, however, the hygroscopicity of lithium dopant usually causes serious moisture instability of devices. Herein, we demonstrate a dopant-free spiro-OMeTAD as hole transporting layer to improve the ambient stability of planar perovskite solar cells. With the optimization of the thickness of spiro-OMeTAD layer, the dopant-free spiro-OMeTAD based device achieved a comparable device performance with a champion power conversion efficiency of 16.92%. Moreover, the unencapsulated dopant-free device showed significantly improved stability, which still maintained 95% of its initial efficiency after storage in ambient environment for 60 days. This work provides a simple and valid approach to overcome the instability issue of spiro-OMeTAD based devices, paving a way to manufacture more stable and efficient perovskite photovoltaics.