Effects of N-Positions on Pyridine Carboxylic Acid-Modified Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) employing NiO film as the hole transport layer (HTL) have been widely investigated due to their good stability. The interface between NiO and perovskite plays a key role in device efficiency and stability, and an interfacial modifier is usually selected to adjust this interface. A good interfacial modifier should not only deduct the energy barrier and passivate trap states at the NiO/perovskite interface but also be beneficial for the growth of perovskite absorbers. Herein, n-pyridine carboxylic acid (n-PA, where n = 2, 3, and 4) isomers with various N-positions are proposed to modify the NiO/perovskite interface. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis show that all isomers are perpendicularly anchored to the NiO surface through ester bonds. The work functions of NiO with n-PA modifications are influenced by the position of the N atom on the pyridine ring. Charge recombination in PSCs is suppressed in varying degrees after n-PA treatment. Moreover, the crystallinity of the perovskite layer is also influenced by the surface modification (i.e., decreased crystallinity for the 2-PA case and increased crystallinity for the 3-PA case). As a result, the device power conversion efficiency (PCE) is achieved in the order of PCE3-PA > PCE4-PA > PCE2-PA > PCENiO. The PSC using a 3-PA-modified NiO film achieves the best PCE of 18.13% due to the reduced energy barrier and thus suppressed recombination in the PSC as well as enhanced absorbance. In addition, with 3-PA modification, the device exhibits good thermal stability and retains 92.5% of its original efficiency after 92 h thermal annealing while only 53.4% for NiO-based devices.