2D-MA 3 Sb 2 I 9 Back Surface Field for Efficient and Stable Perovskite Solar Cells.

In perovskite solar cells (PSCs), a defective perovskite (PVK) surface and cliff-like energy offset at the interface always slow down the charge extraction; meanwhile, interface ion diffusion causes oxidation of the metal electrode, inducing device instability. Here, the in situ grown 2D-(CH 3 NH 2 ) 3 Sb 2 I 9 (MA 3 Sb 2 I 9 ) on the back surface of MAPbI 3 results in a more robust interface. MA 3 Sb 2 I 9 changes the MAPbI 3 surface to p-type and thus acts like a back surface field to drive charge extraction and suppress recombination, resulting in an obviously higher fill factor (FF) = 0.8 and power conversion efficiency (PCE) = 20.4% of SnO 2 /MAPbI 3 /MA 3 Sb 2 I 9 /Spiro-OMeTAD (2,2',7,7'-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene) PSC than the pure MAPbI 3 device. More importantly, strong chemical bonding of SbI prohibits ion diffusion, largely enhancing the thermal stability and longtime stability. Here, special 2D-MA 3 Sb 2 I 9 constructs' robust band alignment and chemical environment at the interface are highlighted for efficient and stable PSCs.