Additive Conformational Engineering To Improve the PbI₂ Framework for Efficient and Stable Perovskite Solar Cells

The PbI₂ framework is critical for two-step fabricated perovskite solar cells. This study investigates the effects of introducing two functional urea-based molecules, biuret (BU) and dithiobiuret (DTBU), into the PbI₂ precursor solution on the absorber layer and overall device performance. BU, which contains C═O, enhanced device performance and stability, whereas DTBU, which contains C═S, had negative effects. Research analysis revealed the differences in the spatial structures of the two urea-based molecules. The introduction of symmetrical BU molecules facilitated the crystallization of PbI₂, whereas the introduction of DTBU with a twisted molecular structure led to inferior crystallization performance of PbI₂. The perovskite thin film, obtained by introducing BU into the PbI₂ precursor solution, demonstrated superior performance, characterized by a decreased defect density and an extended carrier lifetime. The device performance and stability were enhanced, resulting in higher open-circuit voltage and fill factor. The highest achieved power conversion efficiency was 23.50%. After 1300 h of storage under unpackaged conditions at 30-40% humidity, the devices maintained 93% of their initial efficiency. Conversely, the devices prepared with DTBU doping exhibited inferior performance and stability, displaying power conversion efficiency below 10% and faster degradation under the same humidity conditions.