A polyaspartic acid sodium interfacial layer enhances surface trap passivation in perovskite solar cells

The characteristics of perovskite solar cells (PSC) are affected by interface traps. In this work, we introduce an interfacial modifier based on polyaspartic acid sodium (PASP) that is incorporated between a methylammonium lead iodide (MAPbI(3)) photo-absorber and P3CT-Na hole transporting layer. PASP contains a large number of -COO- anions and Na+ cations, thus enabling a strong chelating cooperation for metal polyvalent ions. The incorporated PASP leads to an effective passivation of the surface traps originating from Pb2+ and I- in MAPbI(3) and control over the crystallization of MAPbI(3) with slightly enlarged grains. The combined benefits with the introduced PASP enable boosting the power conversion efficiency to 20.05% with an impressive FF of 82.20% in MAPbI(3) based p-i-n PSCs.