Toward high-efficiency and thermally-stable perovskite solar cells: A novel metal-organic framework with active pyridyl sites replacing 4-tert-butylpyridine

4-tert-butylpyridine (t-BP), the only liquid phase constituent in hole transport layers (HTLs) of perovskite solar cells (PSCs), volatilizes easily to induce the aggregation, hydration, and ion penetration of lithium salts, thereby seriously impairing the thermal stability of devices. Herein, an efficient strategy is presented to address this issue by developing a novel thermally-stable metal-organic framework (MOF) In-Pyia with active pyridyl sites to replace the volatile t-BP. The In-Pyia-modified PSCs realize enhanced power conversion efficiency (PCE) with low performance fluctuation (19.47 ± 0.79%), significantly outperforming the typical devices employing t-BP (17.42 ± 1.02%). More importantly, In-Pyia fulfills a long-term effectiveness to restrain the negative morphological changes of HTL films, attributed to its robust framework and strong coordination effect between pyridine nitrogen atoms and Li⁺ ions. Even after the overnight thermal treatment at 85 °C and subsequent exposure to the ambient environment (25 °C and relative humidity of ~40%) for 16 days without any encapsulation, the In-Pyia-modified PSCs still maintain 80.9% of the initial PCE, while below 20% is left to the t-BP-controlled devices. This is the first example involving a MOF material as the substitute of t-BP, providing a new feasible strategy to fabricate high-efficiency and thermally-stable PSCs.