Vapor Exchange Deposition of an Air-Stable Lead Iodide Adduct on 19% Efficient 1.8 cm2 Perovskite Solar Cells

Air-stable precursor films are critical to reproducibly fabricating the large-area perovskite solar cells (PSCs) in sequential deposition. In traditional sequential vapor approaches, perovskite films suffer from the impingement of hot organic vapor molecules. As a consequence, interfacial voids and structural faults were frequently observed in thick perovskite films (>500 nm) that were formed from simultaneous surface and interfacial nucleation of the perovskite phase. Here, the surface nucleation was suppressed using thermally stable amorphous precursors that could withstand the impingement of hot molecular vapors. We compared the stability of several PbI2 adducts and observed that the PbI2–(1,3-dimethyl-2-imidazolidinone, DMI)) adduct was stable at elevated temperature in air for tens of minutes, providing a sufficient time window for sequential processes. First-principle calculation suggests that DMI adsorbed on PbI2 needs more energy to desorb than DMSO. The adduct films were converted into perovskite phases using vapor exchange deposition (VED). The perovskite phases prepared via VED comprised vertically monolithic grains, indicating a heterogeneous nucleation mechanism. The deposited perovskite films were dense and free of pinholes. Therefore, the shunt resistance of the devices was much higher than those of devices made via traditional vapor approaches. By connecting the ITO electrode symmetrically, we observed that the series resistance varied little with the increase of the device area. Moreover, uniform and kinetically controlled supply of the vapor over a large area facilitated the scale-up of the device area. Finally, we obtained PSCs with power conversion efficiency of 19.2% and 19.0% over active areas of 0.1125 cm2 and 1.8 cm2, respectively. The reported approach opens a promising path for fabricating large-area PSCs without compromising efficiency much.