Dual bulk and interface engineering with ionic liquid for enhanced performance of ambient-processed inverted CsPbI₃ perovskite solar cells

All-inorganic cesium lead iodide (CsPbI₃) perovskites with superior thermal stability are attractive candidates for perovskite solar cells (PSCs). Fabricating such inorganic PSCs in the ambient atmosphere is desirable for practical production, however, the challenge remains in inhibiting the phase transition of CsPbI₃ in ambient air. Herein, we demonstrate a dual bulk and interface engineering using ionic liquid to stabilize CsPbI₃ perovskite structure, thus enhancing the performance of ambient-processed inverted CsPbI₃ PSCs. Such dual bulk and interface engineering is found effective not only in suppressing the bulk and interfacial charge carrier recombination and enhancing charge carrier transport and extraction, but also in protecting CsPbI₃ crystal structure by leaving hydrophobic alkyl chains coverage at the boundary and surface to prevent phase transition caused by moisture from ambient air. The optimized device fully processed in the open air with relative humidity up to 55% exhibits remarkably enhanced efficiency and stability over the control device, with the efficiency increasing from 8.6% to 13.21%, and 92% efficiency maintaining after storage for 1680 h, which outperforms the control device with only 82% retaining after 648 h storage. We thus believe this work can provide an efficient alternative for the low-cost fabrication of ambient-processible PSCs.