Highly efficient A-site cation exchange in perovskite quantum dot for solar cells

The mixed cation colloidal Cs_1-XFA_XPbI₃ perovskite quantum dots (PQDs) obtained by cation exchange between CsPbI₃ and FAPbI₃ PQDs have been reported to exhibit enhanced photovoltaic performance. However, the cation exchange mechanism requires further in-depth investigation in terms of both material properties and device application. In this work, the impact of PQD weight ratio, PQD concentration, and host solvent polarity during cation exchange is comprehensively investigated for the first time. In addition, the whole exchange process under varying conditions is monitored by photoluminescence spectroscopy. As a result, we observe extremely fast cation exchange (∼20 min) under a condition at a CsPbI₃/FAPbI₃ PQD weight ratio of 1:1, a concentration of 70 mg/ml, and a host solvent using toluene. Moreover, we directly fabricate a PQD solar cell device using these obtained mixed cation Cs_0.5FA_0.5PbI₃ PQDs and achieved an enhanced power conversion efficiency of 14.58%. We believe that these results would provide more insights into the cation exchange in emerging PQDs toward efficient photovoltaic fabrication and application.