Tailor-Made Amino-Based Self-Assembled Monolayers Grafted on Electron Transport ZnO Layers: Perovskite Solar Cell Performance and Modified Interface Relationship

Self-assembled monolayers (SAMs) have been grafted via a carboxylic acid group onto a ZnO electron transport layer to control the growth and structure of a hybrid perovskite CH3NH3PbI3 (MAPI) used as an active layer in a solar cell. In addition to the basic molecule, HO2C–PP–NH2 (PP = biphenyl), two bipolar molecules, HO2C–(CH2)n–PP–CH2–NH3Cl (A: n = 0), 4′-(carboxy)-(1,1′-biphenyl)-4-aminomethyl hydrochloride and B: (n = 1), 4′-(carboxymethyl)-(1,1′-biphenyl)-4-aminomethyl hydrochloride, are used in this work. They have been tailored to ensure (i) rigidity/self-assembly and conductivity via biphenyl and (ii) some flexibility via the methylene groups to ensure bonding to both the solid ZnO layer and the methylammonium lead iodide (MAPI) layer. The protonated amino group was chosen to create an efficient 2D sublayer for the growth of the methylammonium-based perovskite. The deposition of SAMs on the metal oxide layers improves device stability and the efficiency of perovskite solar cells (PCSs). The long-term stability of PSCs in ambient air is enhanced by the SAMs.