Researchers develop novel lead leakage blocking and defect healing strategy for perovskite solar cells

Researchers from Shandong University of Science and Technology, Ocean University of China, Qingdao University and Southeast University have developed a method to block lead leakage and heal defects across all interfaces  in perovskite solar cells.

The team utilized a designed MOF: Co-bpdc (where bpdc=4,4’-biphenyldicarboxylate), to modify the top surface of the perovskite. The unique structure and abundant oxygen sites of Co-bpdc enable it to react completely with Pb²⁺, thereby hindering the escape of Pb²⁺ ions. Additionally, they employed polyethyleneimine (PEI), a material commonly used in industrial wastewater treatment, at the buried interface of the perovskite. PEI possesses dense amino groups, enabling it to act as heterogeneous nucleation sites to facilitate the growth of larger grains and enhance film quality. 

Moreover, PEI competes with solvent molecules for PbBr₂ at the burid interface, reducing residual solvent molecules, minimizing voids, thereby forming a perovskite film with a superior buried interface. PEI also protects the perovskite from water molecules and captures escaping Pb²⁺ ions, effectively suppressing lead leakage.

This method offers a comprehensive system that impedes lead leakage, optimizes crystallization, and reduces interface defects in PSCs. When applied to FA_0.945MA_0.025Cs_0.03Pb(I_0.975Br_0.025)₃ and CsPbBr₃ PSCs, it improved their PCEs to 24.92% and 11.17%, demonstrating the universality of this all-interfaces engineering method for different perovskite compositions. 

Importantly, experiments have shown that this method provides protection for PSCs by preventing water molecule infiltration and effectively suppressing lead leakage. 

After 1200 hours of storage under conditions of 25 ^oC with 85% relative humidity (RH) and 85 ^oC with 0% RH, unencapsulated PSCs still maintained 93.7% and 94.5% of their initial efficiency, respectively. Additionally, after 360 hours of continuous operation, the device still maintains 94.2% of its initial PCE.

This innovative protection system for PSCs by uses a non-ionic polymer, PEI, and a synthesized MOF material, Co-bpdc, at both the buried and top interfaces of the perovskite film. It effectively heals defects at these interfaces while reducing the risk of lead leakage. This method reduces the problem of toxicity of lead ions and improves the performance of PSCs, thereby presenting a valid way to advance their commercialization.