Spacer Engineering Using Aromatic Formamidinium in 2D/3D Hybrid Perovskites for Highly Efficient Solar Cells

Organic spacers play an important role in 2D/3D hybrid perovskites, which could combine the advantages of high stability of 2D perovskites and high efficiency of 3D perovskites. Here, a class of aromatic formamidiniums (ArFA) was developed as spacers for 2D/3D perovskites. It is found that the bulky aromatic spacer ArFA in 2D/3D perovskites could induce better crystalline growth and orientation, reduce the defect states, and enlarge spatially resolved carrier lifetime thanks to the multiple NH···I hydrogen-bonding interactions between ArFA and inorganic [PbI₆]^4- layers. As a result, compared to the control device with efficiency of 19.02%, the 2D/3D perovskite device based on such an optimized organic salt, namely benzamidine hydrochloride (PhFACl), exhibits a dramatically improved efficiency of 22.39% along with improved long-term thermal stability under 80 °C over 1400 h. Importantly, a champion efficiency of 23.36% was further demonstrated through device engineering for PhFACl-based 2D/3D perovskite solar cells. These results indicate the great potential of this class of ArFA spacers in highly efficient 2D/3D perovskite solar cells.