Spectroscopic ellipsometry and solar cell performance of Cs-doped MA<inf>0.05</inf>FA<inf>0.95</inf>Pb(I<inf>0.98</inf>Br<inf>0.02</inf>)<inf>3</inf> triple cation perovskite thin films for solar cell applications

Abstract

FA0.95MA0.05Pb(Br0.02I0.98)3(CsI)x (x = 0, 0.02, 0.05, 0.07) thin films were formed in a dry air atmosphere. The influence of different ratios of CsI-doping on the formed phases, crystallinity, emitted colors and different optical parameters were explored in detail. The spectroscopic ellipsometry (SE) spectra were analyzed using the Kramers–Kronig model. A device based on the film with free Cs has a short-current density (JSC) of 20.18 mAcm− 2, an open-circuit potential (VOC) of 0.972 V, a fill factor (FF) of 0.67, and a power conversion efficiency (PCE) of 13.04%. VOC was improved (1.029 V) as the film was doped with 2% Cs, while it was reduced as the films were doped with other higher Cs ratios. The current density (JSC) exhibited the highest value (20.18 mA/cm2) in the undoped and doped films with 2% Cs and it was reduced with further Cs doping. The FF and PCE were increased slightly (0.67 and 13.83%) as the film was doped with 2% Cs, while these two parameters were reduced as the films were doped with further Cs amounts.