Improved carriers injection capacity in perovskite solar cells by introducing A-site interstitial defects

Organic-inorganic hybrid perovskite solar cells have emerged as a promising candidate for next generation solar cells. The most extensively used perovskite absorber is methylammonium lead iodide (MAPbI₃). Defect types and quantities, particularly for the defects involving A-site cation (MA⁺), appear to have significant influence on material properties and on the solar cell performance. In this report, by introducing a smaller sized potassium cation (K⁺) into the lattice structure of MAPbI₃, the photovoltaic performance of mixed-cation perovskite solar cells was enhanced. X-ray diffraction data indicate that the K⁺ mainly occupied the interstitial position in the perovskite crystal lattice. Systematic study has demonstrated that there are several benefits of introducing the proper amount of K⁺ to MAPbI₃. The increased crystallinity, red shifted photoluminescence (PL) spectra and decreased surface potential result in eminent carrier separation properties and thus reduce the charge recombination in solar cell devices. The optimized mixing range has been investigated; when 0 ≤ K⁺ content of x (x is the ratio of K⁺:Pb²⁺) ≤ 0.2, the modified mixed perovskite solar cell exhibited better photoelectric conversion efficiencies than that of pristine MAPbI₃. Particularly, the perovskite solar cell presents balanced injection capacity for both holes and electrons when x = 0.2, and a conversion efficiency of 19.3% is obtained.