Impedance spectroscopy of perovskite/contact interface: Beneficial chemical reactivity effect

Understanding chemical reactivity of lead halide perovskite materials with contacts is crucial to improve the stability of these optoelectronic devices. The study of the physical and chemical interactions at the interfacial region is still one of the most challenging tasks in this field. We investigate a configuration based on the direct contact of gold (Au) with highly crystalline methylammonium lead bromide perovskite (MAPbBr₃), in comparison with the presence of an organic interlayer. The metal contact clearly shows the double layer capacitance that can be monitored by Impedance Spectroscopy (IS). Measurements in the dark reveal the frequencies where a reduction in charge accumulation occurs, related to ionic reactivity with the external contacts. Under light, this chemical reaction is favored and the newly formed contact improves the performance of the solar cell. The IS results show that reactivity proceeds at timescales longer than 100 s, reducing the recombination kinetics under 1 sun illumination conditions, increasing the photovoltage and photocurrent that can be extracted. This work presents IS as a nondestructive in operando tool to monitor the kinetics of the ionic double layer formation and the reactivity of methylammonium bromide perovskite material with contacts decoupling as well this information from other resistive and capacitive contributions.