Trap-State Passivation by Nonvolatile Small Molecules with Carboxylic Acid Groups for Efficient Planar Perovskite Solar Cells

Trap-state passivation has been validated to efficiently improve the performance of perovskite solar cells. Small volatile molecules and polymers both have the ability to reduce the trap states in perovskite. Herein, we demonstrate the feasibility of passivation by nonvolatile small molecules with carboxylic acid groups such as benzoic acid, p-phthalic acid, and trimesic acid. They can obviously increase the fill factor of the photocurrent density-voltage curves. Furthermore, the relationship between the molecular structure and passivation effect is proposed by fixing the concentration of carboxylic acid groups. Trimesic-acid-doped perovskite solar cells significantly increase the power conversion efficiency from 12.52 +/- 0.67 to 14.51 +/- 0.81 (champion efficiency, 15.81%) under standard AM 1.5G illumination. Our work expands the chemical additives in perovskite and further demonstrates how the additive molecular structure influences the performance of solar cells.