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

Abstract

Cesium‐formamidinium lead triiodide perovskite quantum dot (CsxFA1‐xPbI3 PQD) is very promising for photovoltaic applications due to its good phase stability and outstanding optoelectronic properties. However, achieving the CsxFA1‐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 CsxFA1‐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, CsxFA1‐xPbI3 PQD solar cells deliver an efficiency of up to 17.49%, which is the highest value of CsxFA1‐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.