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

Cesium-formamidinium lead triiodide perovskite quantum dot (Cs_xFA_1-xPbI₃ PQD) is very promising for photovoltaic applications due to its good phase stability and outstanding optoelectronic properties. However, achieving the Cs_xFA_1-xPbI₃ 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 (FABF₄), is applied for the cation exchange and stabilizing surface matrix of PQDs. The results reveal that the FA⁺ of FABF₄ molecules could exchange the Cs⁺ of CsPbI₃ PQDs forming alloy Cs_xFA_1-xPbI₃ PQDs, allowing to tune the spectroscopies of PQDs. Meanwhile, the BF₄ ^- of FABF₄ 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_xFA_1-xPbI₃ PQD solar cells deliver an efficiency of up to 17.49 %, which is the highest value of Cs_xFA_1-xPbI₃ 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.