Surface Matrix‐Mediated Cation Exchange of Perovskite Quantum Dots for Efficient Solar Cells

Abstract Cesium‐formamidinium lead triiodide perovskite quantum dot (Cs x FA 1‐x PbI 3 PQD) is very promising for photovoltaic applications due to its good phase stability and outstanding optoelectronic properties. However, achieving the Cs x FA 1‐x PbI 3 PQDs with tunable compositions and robust surface matrix remains a challenge. Here, the surface matrix‐mediated cation exchange of PQDs is proposed, in which a bi‐functional molecule, tetrafluoroborate methylammonium (FABF 4 ), is applied for the cation exchange and stabilizing surface matrix of PQDs. The results reveal that the FA + of FABF 4 molecules could exchange the Cs + of CsPbI 3 PQDs forming alloy Cs x FA 1‐x PbI 3 PQDs, allowing to tune the spectroscopies of PQDs. Meanwhile, the BF 4 − of FABF 4 molecules can effectively stabilize the surface lattice and substantially diminish the surface vacancies of PQDs, improving the phase stability and optoelectronic properties of PQDs. Consequently, Cs x FA 1‐x PbI 3 PQD solar cells deliver an efficiency of up to 17.49 %, which is the highest value of Cs x FA 1‐x PbI 3 PQD solar cells. This work provided important design principles for the composition and surface matrix regulation of PQDs for high‐performance solar cells or other optoelectronic devices.