Approach To Enhance the Stability and Efficiency of Triple-Cation Perovskite Solar Cells by Reactive Antisolvents

Controlling thin-film crystallization kinetics of perovskites is vital for the fabrication of highly efficient and stable perovskite solar cells (PSCs). Because of the low solubility of lead halogen derivatives in dimethylformamide solvent and poor film quality, addition of dimethylsulfoxide (DMSO) to the solution as a cosolvent has a great effect on the crystallization kinetics and morphology of perovskite thin films. However, Pb-DMSO and residual DMSO complexes that are difficult to be removed from the structure can lead to structural deformations and stability issues. Here, two different reagents such as benzyl chloride (BCl) and benzyl bromide (BBr) are applied as antisolvents to eliminate these problems utilizing the Kornblum oxidation reactions in the triple-cation perovskite thin films formed by the one-step coating method. Electrochemical impedance spectroscopy (EIS) analysis has been carried out to explain the charge transfer resistances and capacitive behaviors under illuminated conditions. EIS measurements show that washing with BBr antisolvent reduces the charge recombination in PSCs and leads to the best device performance with improved charge transport, yielding a 19.2% power conversion efficiency with a higher open circuit voltage (V-oc) of 1100 mV compared to washing with chlorobenzene (CB) and BCl. Resistances at the low-frequency region in Nyquist complex plots associated with charge recombination resistances were measured to be 1430, 564, and 3000 ohm, which are in good agreement with short circuit currents 23.3, 23.1, and 24.8 mA/cm(2) for devices fabricated with CB, BCI, and BBr, respectively. Removal of the residual DMSO and PbDMSO complexes via washing with BBr results in achieving more stable and highly efficient solar cells, which maintained 94% of the initial efficiency after 1 month.