In this work, a study of a characterization technique based on open circuit voltage decay is carried out to obtain the recombination resistance of mobile charge carriers and ionic migration in triple cation perovskite solar cells. The devices were fabricated with the structure FTO/TiO₂/Cs_0.05FA_1−XMA_XPb(I_1−XBr_X)₃/spiroOMetad/Au. An equivalent circuit, created in Ngspice, was developed adjusting the capacitance and resistance values to fit the experimental open circuit voltage (V_oc) decay curves observed. The aim of this study is to associate the perovskite ionic migration with the V_oc characteristic time of charge transport in triple cation perovskite solar cells. Thus, an analysis of the open circuit voltage transient behavior was made by taking measurements of the photovoltage as a function of time. The results indicate that the technique shows charge recombination while the device is illuminated. In addition, an enhancement of the recombination resistance when increasing the FA⁺ concentration was observed. Finally, the transient behavior was associated with MA⁺, FA⁺, Cs⁺ and I⁻ migration, obtaining an ionic mobility in the range between 10⁻¹⁰ to 10⁻¹² cm² (Vs)⁻¹.

Usando el método de la matriz de transferencia y la ecuación de Ben Daniel y Duke para propagación de electrones con masa variable, calculamos la transmitancia para una superred lineal finita simétrica que tiene variación lineal del ancho de las barreras de potencial. El ancho de las barreras decrece del centro hacia los extremos de la superred. La dependencia en la energía de la transmitancia presenta intervalos de bandas de rechazo y de bandas bastante planas de transmisión. Realizamos los cálculos de transmisión para varias alturas de barreras y varios anchos de pozos. Comparamos con la transmisión de una superred regular en la cual todas las barreras tienen el mismo ancho. También comparamos con la de una superred lineal invertida en que el ancho de las barreras crece del centro hacia afuera, así como con la de una estructura donde la variación de los anchos de barreras sigue un perfil gaussiano. Using the transfer matrix method and the Ben Daniel-Duke equation for variable mass electrons propagation, we calculate the transmittance for a symmetric finite superlattice which has a linear dependence for the width of the potential barriers. The width of the barriers decreases from the center toward to the ends of the superlattice. The energy dependence of the transmittance presents intervals of stopbands and quite flat passbands. We calculate the transmission for several heights of barriers and widths of wells and compare with the transmission of a regular superlattice where all the barriers have the same width. We also compare with an inverted linear superlattice where the barriers width increases from the center to the ends, as well with the transmission produced by a superlattice with a Gaussian variation of the barriers width.