Optical Determination of Carrier Concentrations in ITO, PEDOT:PSS, and (FASnI3)0.6(MAPbI3)0.4 within a PV Device

A low bandgap mixed tin-lead (Sn-Pb) halide perovskite based thin film solar cell is a multilayer stack consisting of indium tin oxide (ITO) as the transparent front electric contact, poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the hole transport layer, low bandgap perovskite (FASnI3)0.6(MAPbI3)0.4 as the absorber layer, fullerene (C60) as the electron transport layer, bathocuproine (BCP) as the hole blocking layer, and Ag as the back contact. Determination of carrier concentration (N) of these individual layers in the solar cell stack structure using direct electrical measurements is not accessible. Here, N for some component layers in a low bandgap organic inorganic (FASnI3)0.6(MAPbI3)0.4 absorber based perovskite solar cell are determined using non-contacting magnetic field dependent terahertz (THz) range spectroscopic ellipsometry for optical Hall effect measurement to ascertain the free carrier optical absorption and corresponding N using the Drude model. From THz spectral range optical Hall effect measurements and analysis, N of the ITO, PEDOT:PSS, and low bandgap (FASnI3)0.6(MAPbI3)0.4 are determined to be (2.8 ± 0.6), 1020 cm ⁻³ , (2.6 ± 0.4), 1022 cm ⁻³ , and (1.5 ± 0.1), 1018 cm ⁻³ , respectively. All values are within expectations for this device design. These results demonstrate the capability of THz range optical Hall effect measurements to determine transport properties of layers within complete thin film polycrystalline solar cells, and the properties determined can be used as input for photovoltaic device modeling to understand device physics and optimize performance.