Unraveling the Impact of Rubidium Incorporation on the Transport-Recombination Mechanisms in Highly Efficient Perovskite Solar Cells by Small-Perturbation Techniques

We applied intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS) techniques to explore the effect of rubidium (Rb) incorporation into lead halide perovskite films on the photovoltaic parameters of perovskite solar cells (PSC). IMPS responses revealed the transport mechanisms at the TiO₂/perovskite interface and inside the perovskite absorber films. For recombination time constants, IMVS showed that the two perovskite solar cells differ in terms of trap densities that are responsible for recombination loss. Impedance spectroscopy carried out under illumination at open circuit for a range of intensities showed that the cell capacitance was dominated by the geometric capacitance of the perovskite layer. Our systematic studies revealed that Rb containing PSCs exhibit enhanced charge transport, slower charge recombination, faster photocurrent transient response, and lower capacitance than the Rb-free samples