Suppressing Glass‐Transition and Lithium‐Ions Migration in Hole Transport Layer by V2O5 Decorated Graphite Carbon Nitride Nanosheets for Thermally Stable Perovskite Solar Cells

The undesired glass transition of 2,2’,7,7’‐tetrakis(N,N‐di‐ p ‐methoxyphenylamine)‐9,9’‐spirobifluorene (spiro‐OMeTAD) and the lithium‐ions migration are the intractable factors affecting the stability of perovskite solar cells (PSCs). Herein, the 2D graphite carbon nitride nanosheets (CNVx) with various loading masses of V 2 O 5 are developed as additives for spiro‐OMeTAD to achieve stable and efficient PSCs. The optimized CNVx possesses quantitative and controllable oxidation ability to spiro‐OMeTAD under the inert atmosphere, yielding significantly improved conductivity and hole mobility of the modified hole transport layer (HTL) film. As a result, a power conversion efficiency (PCE) of 21.10% is obtained in the CNVx modified device with enhanced open‐circuit voltage of 1.114 V and fill factor of 0.80. Furthermore, the glass transition temperature suppression in the CNVx‐modified HTL film and effective Li + ions capture significantly improve the stability of the unencapsulated device, which maintains 82% and 90% of the original PCE after aging at 85 °C in the N 2 atmosphere and storing in an ambient atmosphere with a relative humidity of 40% for 720 h, respectively. These results provide a deep understanding of PSCs stability enhancement with 2D carbon nanosheets for realizing high‐performance PSCs.