Reduced defects and enhanced V_bi in perovskite absorbers through synergetic passivating effect using 4-methoxyphenylacetic acid

Surface defect-assisted non-radiative recombination is one of major detrimental factors limiting the development of efficient and stable perovskite solar cells (PSCs). The ionic characteristic of perovskite absorbers facilitates passivation of diverse defects through the interaction of specific ending functional groups of organic molecules. Here, the passivation mechanism of a bifunctional organic molecule, 4-methoxyphenylacetic acid (MPA), on the defects within perovskite absorbers is systematically investigated. Density functional theory and X-ray photoelectric spectroscopy confirm that the keto-oxygen atom of carboxylic acid in the MPA mainly passivates Pb–I antisite through Lewis base-acid interaction, while the O-donor of the methoxy group from MPA heals the undercoordinated Pb²⁺ on the perovskite absorbers surface via a coordination bond. The synergetic passivation of two functional groups significantly reduces the defect density and thus recombination loss, which is confirmed by the space charge limited current, time-resolved photoluminescence (PL) spectroscopy and PL mapping. The capacitance-voltage measurement proves that MPA treatment enhances the built-in potential to accelerate the separation of photogenerated charges within perovskite absorbers. As a result, MPA-treated PSCs achieve a champion efficiency of 22.32% (relatively to 20.97% of the control) coupled with improved environmental tolerance for PSCs on ITO/glass and 19.34% for PSCs on flexible ITO/polyethylene terephthalate.