Addition of Lithium Iodide into Precursor Solution for Enhancing the Photovoltaic Performance of Perovskite Solar Cells

Lithium iodide is mixed into the perovskite precursor solution as an additive. X-ray diffraction, field-emission scanning electron microscopy, steady-state photoluminescence, ultraviolet-visible absorption spectra, and electrochemical impedance spectra are used to characterize and analyze the perovskite solar cells prepared from this solution. It is found that the LiI additive can improve the crystallinity and the quality of perovskite crystal, enhance the light absorbance and the charge carrier extraction of the perovskite films, and reduce the charge-transfer resistance of the device. As a consequence, the open-circuit voltage and the fill factor of the perovskite solar cells increase. Under optimal conditions, the LiI-containing perovskite solar cell can achieve a power conversion efficiency of 16.53% whereas the device based on a perovskite without added LiI has an efficiency of 14.22% under the same experimental conditions. The simple process and significant improvement in the performance render this method promising.