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

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