Surface Ligand Management for Stable FAPbI₃ Perovskite Quantum Dot Solar Cells

In contrast to conventional colloidal quantum dots (CQDs), management of insulating ligands on perovskite CQDs is challenging because their ionic bonds are highly vulnerable to polar solvents. Consequently, there have been only a few examples of perovskite CQD solar cells incorporating relatively robust inorganic perovskite of which optoelectronic properties are not ideal for photovoltaic devices. Here, we report efficient and stable CQD solar cells based on formamidinium lead triiodide (FAPbI₃) CQDs realized by rational surface regulation. Tailoring polarity of antisolvents for the post-synthetic process enabled effective removal of the insulating ligands on FAPbI₃ CQDs while preserving perovskite cores. Owing to the enhanced inter-dot electrical coupling, a power-conversion efficiency of 8.38% was demonstrated. Furthermore, the FAPbI₃ CQDs-based devices showed superior stability over those of bulk FAPbI₃ devices. Thermodynamic and crystallographic analyses revealed that enhanced contribution of the surface energy and lattice contraction contribute to their superior stability. Halide perovskite colloidal quantum dots (CQDs) have emerged as a promising candidate for CQD optoelectronics. As-synthesized CQDs are stabilized by long organic ligands to prevent undesirable aggregation. Effective removal of the insulating ligands is prerequisite for promoting electrical coupling between CQDs. However, the ionic bonding character of the perovskite CQDs makes them highly vulnerable to polar solvents used for surface treatment, posing difficulty in handling the insulating ligands. Here, we propose a rationally designed post-synthetic process for effective control of ligand density on formamidinium lead triiodide (FAPbI₃) CQDs. The resulting FAPbI₃ CQD solar cells demonstrated power-conversion efficiency of 8.38% with stability superior to those of bulk FAPbI₃ devices. To the best of our knowledge, this is the first demonstration of FAPbI₃ CQDs photovoltaics. Our strategy will provide an important insight into efficient and stable perovskite CQD optoelectronics. Effective management of the insulating ligands is prerequisite for achieving good electrical coupling between colloidal quantum dots (CQDs) and, thus, high-performance solar cells. Here, we developed a rationally designed post-synthetic process for effective control of ligand density on organic-inorganic hybrid formamidinium lead triiodide (FAPbI₃) perovskite CQDs. The resulting FAPbI₃ CQD solar cells demonstrated power-conversion efficiency of 8.38% with stability superior to that of bulk FAPbI₃ devices.