Linear and nonlinear optical properties of CsI-doped FA<inf>0.95</inf> MA<inf>0.05</inf>Pb(I<inf>0.98</inf>Br<inf>0.02</inf>)<inf>3</inf> triple cation perovskite thin films

Abstract

FA0.95MA0.05 Pb(Br0.02I0.98)3(CsI)x (x = 0.02, 0.05, and 0.07) perovskite films were deposited using a single-step deposition procedure. The effect of CsI doping on the absorption coefficient, transmittance, reflectance, extinction coefficient, electric and nonlinear parameters of FA0.95MA0.05 Pb(Br0.02I0.98)3(CsI)x perovskite films was explored. The determined direct optical bandgap for undoped FA0.95MA0.05Pb(Br0.02I0.98)3 film is 1.51 eV, which reduced slightly to 1.5 eV for the 2% CsI doped film. When the doping amount increased to 5 and 7% CsI, two bandgaps appeared with energy values (1.22, 1.53) and (1.3, 1.55) eV, respectively. For the wavelength range 300–800 nm, the film with 5% CsI attained the highest absorption coefficient, while the film with 7% CsI attained the highest refractive index. At 500 nm, the refractive index values for undoped and doped films with 2, 5 and 7% CsI are 1.42, 1.37, 2.09 and 2.24, respectively.