Effect of 1,3-Disubstituted Urea Derivatives as Additives on the Efficiency and Stability of Perovskite Solar Cells

Additive engineering in perovskites precursor solution is one of the most effective methods to fabricate high-quality perovskite films. Finding proper additives for morphology improvement and passivation of the perovskite defects is critical to fabricate highly efficient and stable perovskite solar cells (PSCs). In this work, 1,3-disubstituted urea additives are employed to study the effect of different substituents at -NH moiety on the quality of the perovskite layer and device performance. By adding 1,3-diphenyl urea (Ph-urea) or 1,3-di(tert-butyl)urea (tBu-urea) into the precursors, the crystallization process leads to the formation of perovskite films with larger grains and lower defect densities as compared to the non-substituted urea additive. Using density functional theory (DFT) calculations and experimental spectroscopic measurements, we found that the selected 1,3-disubstituted ureas are prone to form stronger coordination interaction with undercoordinated Pb2+ ions than the urea. Applying this additive engineering to the devices reduced the current density–voltage (J–V) hysteresis and improved the photovoltaic performance, resulting in maximum power conversion efficiencies of 21.7% and 21.2% for the Ph-urea and tBu-urea modified devices, respectively. In addition, the device with Ph-urea enhanced long-term stability, where it remains 90% of its initial efficiency, while the device with tBu-urea degrades fast reaching 20% of its initial efficiency after aging for 90 days due to the high moisture permeability of tBu-urea.