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

This study reveals that the molecularconformation of theadditives makes a nonnegligible effect on the PbI2 filmsand the final perovskite solar cells (PSCs) performance. The spatiallysymmetrical biuret additive contributes to the improved crystallinityof PbI2 film, while the asymmetrical dithiobiuret additivealmost destroys the PbI2 film. Therefore, the biuret-modifiedPSCs via a two-step deposition method achieve an enhanced power conversionefficiency of 22.7%, negligible hysteresis, and prolonged stability. The PbI2 framework is critical for two-stepfabricatedperovskite solar cells. This study investigates the effects of introducingtwo functional urea-based molecules, biuret (BU) and dithiobiuret(DTBU), into the PbI2 precursor solution on the absorberlayer and overall device performance. BU, which contains C O,enhanced device performance and stability, whereas DTBU, which containsC S, had negative effects. Research analysis revealed the differencesin the spatial structures of the two urea-based molecules. The introductionof symmetrical BU molecules facilitated the crystallization of PbI2, whereas the introduction of DTBU with a twisted molecularstructure led to inferior crystallization performance of PbI2. The perovskite thin film, obtained by introducing BU into the PbI2 precursor solution, demonstrated superior performance, characterizedby a decreased defect density and an extended carrier lifetime. Thedevice performance and stability were enhanced, resulting in higheropen-circuit voltage and fill factor. The highest achieved power conversionefficiency was 23.50%. After 1300 h of storage under unpackaged conditionsat 30-40% humidity, the devices maintained 93% of their initialefficiency. Conversely, the devices prepared with DTBU doping exhibitedinferior performance and stability, displaying power conversion efficiencybelow 10% and faster degradation under the same humidity conditions.

Automated summary

This study reveals that the molecular conformation of the additives significantly affects the PbI2 films and the performance of perovskite solar cells (PSCs). The symmetrical biuret additive improves the crystallinity of the PbI2 film, while the asymmetrical dithiobiuret additive damages the PbI2 film. Therefore, the biuret-modified PSCs achieve enhanced power conversion efficiency, negligible hysteresis, and prolonged stability.