Facilitated Diffusion of Organic Ammonium Salts via OD-Induced Porous PbI2 for Efficient Two-Step Inverted Perovskite Solar Cells
The pre-deposited lead iodide (PbI2) film in two-step inverted perovskite solar cells (PSCs) often exhibits a dense structure, which impedes the diffusion and reaction of organic ammonium salts, leading to unreacted PbI2 residues and compromised device performance. To address this, 2,4-oxazolidinedione (OD) is introduced as a molecule additive into the PbI2 precursor solution. Owing to its stronger coordination with PbI2, OD effectively modulates its crystallization behavior, resulting in a porous structure. This porous structure significantly facilitates the diffusion and infiltration of organic ammonium salts, thereby minimizing PbI2 residue and enhancing the completeness of the perovskite conversion. Furthermore, OD and the constructed porous network jointly retard the crystallization kinetics of perovskite, promoting the formation of perovskite films with improved crystallinity and preferred crystal orientation. Therefore, the optimized PSCs achieve a power conversion efficiency (PCE) of 26.31%, and demonstrate excellent operational stability, retaining 90.24% of initial PCE for 1500 h at 25°C and 90.47% after 1000 h at 65°C. The champion device exhibits a VOC of 1.197 V, a JSC of 26.28 mA cm-2, and an FF of 83.58%, with negligible hysteresis. This study presents a straightforward yet effective approach to advancing the performance and stability of inverted PSCs fabricated via the two-step method.