Identifying the charge generation dynamics in a Cs+-based triple cation mixed perovskite solar cells

Triple cation based perovskite solar cells offers enhanced moisture tolerance and stability compare to mixed perovskites. A slight substitution of methyl ammonium or formamidinium cation by cesium (Cs+), was also reported to eliminate halide segregation due to its smaller size. To elucidate the device kinetics and understand the role of Cs, we undertook different mode of scanning probe microscopy and electrochemical impedance spectroscopy (EIS) experiments. Kelvin probe force microscopy revealed that the incorporation of Cs cation increases the contact potential difference (CPD), this CPD further increases when Spiro-OMeTAD was used as a hole transport material. The current at nanoscale level shows improvement with Cs inclusion and further enhancement by the Spiro-OMeTAD coating under illumination, which supports the high photocurrent density obtained from the cells. EIS demonstrates that in a triple cation environment, reduce carrier recombination at the TiO2 /perovskite interface was also obtained which in turn allow to acheive higher Voc value