Dual Modification Engineering via Lanthanide‐Based Halide Quantum Dots and Black Phosphorus Enabled Efficient Perovskite Solar Cells with High Open‐Voltage of 1.235 V

Abstract Interfacial engineering is one of the most effective means to improve the photoelectric conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). In this work, Ln 3+ ‐based halide Cs 3 TbCl 6 quantum dots (QDs) are synthesized through a modified hot‐injection method, which displays an excitonic emission centered at 431 nm and the characteristic emission peaks of Tb 3+ ions. Then, the Ln 3+ ‐based halide Cs 3 TbCl 6 QDs are introduced to the interface of Cs 0.05 (FA 0.83 MA 0.17 ) 0.95 Pb(I 0.83 Br 0.17 ) 3 perovskite films in the PSCs, which can regulate the energy levels, fill the grain boundaries and remove the ionic defects. Surprisingly, the Cs 3 TbCl 6 QDs modified devices achieve a champion PCE of 22.89% with a super high open‐voltage of 1.235 V. The high open‐voltage can be mainly attributed to the better bandgap alignment, enhanced interface, and reduced defects density. Afterward, the hole transport layer (HTL) is modified by the black phosphorus QDs (BPQDs), yielding a champion PCE of 23.49% and a filling factor of 80.32%. The Cs 3 TbCl 6 QDs modified unencapsulated device possesses well environmental stability and humidity stability. This work demonstrates a new kind of Ln 3+ ‐based metal QDs and explores a new approach to fabricate the PSCs with high open‐voltage, high efficiency, and good stability through the QD‐based passivation techniques.