Bipedal Anchoring Strategy via Dicarboxylic Acid Molecules for Efficient NiOx-Based Perovskite Solar Cells

Abstract

Though nickel oxide (NiO_x) has been widely used as a hole transport layer in inverted perovskite solar cells (PSCs), the performance of NiO_x-based PSCs is limited by low conduction of NiO_x, surface defects, lattice mismatch, poor energy level alignment, and redox reactions at the NiO_x/perovskite interface. To address these issues, a series of small dicarboxylic acid molecules (DAMs) are introduced as a buffer layer between NiO_x and the perovskite films in this study. Utilizing the double carboxylic acid moieties to orderly anchor NiO_x, DAMs effectively passivate defects of NiO_x and inhibit interfacial redox reactions. Among the DAMs, pyridine-3,5-dicarboxylic acid (P35DA) owns unique pyridine rings, which induce more favorable dipole moments for energy level alignment and interact with uncoordinated lead ion, thus regulating the crystallization of perovskite, reducing the interfacial tensile strain, and suppressing nonradiative recombination. Consequently, the devices based on NiO_x/P35DA exhibit the champion power conversion efficiency (PCE) of 24.05% and 21.48% for 1.56 and 1.68 eV PSCs, respectively. Meanwhile, the unencapsulated devices maintain 81% of their initial PCE after being stored in air with 50–60% relative humidity for 1200 h, exhibiting remarkable environmental stability.