Enhancing Photostability of Perovskite Solar Cells by Eu(TTA)<sub>2</sub>(Phen)MAA Interfacial Modification

Organic–inorganic lead halide perovskite solar cells (PSCs) exhibit spectacular changes in the photovoltaic area, but they still face the challenges of full spectral utilization and photostability under continuous light irradiation. The ultraviolet (UV) part in sunlight could induce oxygen vacancy in the mesoporous TiO<sub>2</sub> (m-TiO<sub>2</sub>) layer, resulting in the degradation of perovskite photoactive films and the rapidly decreased device performance. In this work, we demonstrate that an effective luminescent downconversion material, Eu­(TTA)<sub>2</sub>(Phen)­MAA (ETPM), can be used as an interfacial modifier between the m-TiO<sub>2</sub> layer and the perovskite photoactive layer to improve the power conversion efficiency (PCE) from 17.00 to 19.07%. The improved device performance can be ascribed to the effective utilization of incident UV light and reduced carrier recombination. Meanwhile, the conversion of the UV light by ETPM could inhibit the stability loss of the device under irradiation. As a result, the modified PSCs can maintain 86% of their initial value under continuous light soaking for 100 h, higher than that of 40% for the control device. This work indicates that the introduction of the luminescent downconversion material ETPM can successfully improve the PCE and photostability of PSCs.