Employment of l-Citrulline as an Effective Molecular Bridge for Regulating the Buried Interface of Perovskite Solar Cells to Achieve High Efficiency and Good Stability

Suppressing the defects from SnO₂ and perovskite interface is essential for the fabrication of large-area n–i–p perovskite solar cells (PSCs) with the needed lifetime and efficiency for commercialization. Here, we report the employment of l-citrulline (CIT), which has amino acid (─COOH, ─NH₂) and urea (─NH─CO─NH₂) groups, during SnO₂ colloidal dispersion to function as a molecular bridge to modulate the SnO₂/perovskite buried interface. The amino acid group can effectively coordinate with Sn⁴⁺ to passivate the oxygen vacancy defects of SnO₂, and the urea group can interact with uncoordinated Pb²⁺ and I⁻. These interactions not only improve the electron mobility of SnO₂ but also facilitate the formation of larger grain-size perovskite film. In addition, they can also inhibit the generation of excess PbI₂ and the nonphotoactive δ phase to result in suppressed trap-assisted nonradiative recombination. Consequently, the incorporation of CIT helps achieve a champion power conversion efficiency (PCE) of 25.95% (0.07065 cm²) in PSC with improved shelf life/light soaking stability. When combined with an antisolvent-free slot-die coating technique in air, the solar modules (23.26 cm²) could achieve a PCE of 22.70%, which is among the highest PCE reported so far.