Performance of planar perovskite solar cells based on formamidinium cations: Simulation and fabrication

The best efficiency ever recorded for state-of-the-art perovskite solar cells (PSCs) is about 25% where the formamidinium (FA)-dominated perovskites were adopted. But the optimum content of FA perovskite solar cells based on Cs-0.05(FA(x)MA([1-x]))(0.95)Pb(I0.83Br0.17)(3) films has yet to materialize the high-power conversion efficiency. Herein, high quality and uniform perovskite films constituting Cs-MA-FA (Cesium; Methylammonium) mixed cation in the A-site of the ABX(3) structure with different FA content are synthesized by a typical spin coating based antisolvent technique. Because of the limitations of perovskite and solar cell materials, the influences of various FAs on the device performance are analyzed through device simulation. From the synthesized films, the band gap equation of Cs-0.05(FA(x)MA([1-x]))(0.95)Pb(I0.83Br0.17)(3) has been estimated, ranging from 2.175 eV to 1.5 eV for various FA/(FA + MA) ratios respectively. Ultimately, the highest conversion efficiency of the planar solar cell based on graded perovskite with various FA content was obtained for the case where the positive Eg grading consists of the Eg of 2.175 eV at the front (FA/[FA + MA] of 0) and the E-g of 1.5 eV at the back (FA/[FA + MA] of 1). The Cs-0.05(FA(0.87)MA(0.13))(0.95)Pb(I0.83Br0.17)(3) cell achieved an AM1.5G conversion efficiency of around 20.98%, showing improved V-OC, J(SC), and FF among the planar perovskite solar cells with different x.