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Perovskite Solar Cell Modeling Using Light- and Voltage-Modulated Techniques

Ravishankar, Sandheep, Aranda, Clara, Sanchez, Sandy, Bisquert, Juan, Saliba, Michael, Garcia-Belmonte, Germà
Journal of physical chemistry 2019 v.123 no.11 pp. 6444-6449
anions, annealing, capacitance, dielectric spectroscopy, electric current, electric potential difference, models, physical chemistry, solar cells
The analysis of the impedance spectroscopy (IS) data of perovskite solar cells (PSCs) has been challenging so far, with the low-frequency phenomena in particular yielding ambivalent results and interpretations. We tackle this problem by carrying out intensity-modulated photocurrent spectroscopy (IMPS) measurements at open-circuit (OC) conditions on CH₃NH₃PbBr₃ cells prepared by the flash infrared annealing method with different electron-selective contacts. We identify the existence of a capacitance of the order 10–⁴ F·cm–² that is not discernible from IS measurements, which is attributed to the accumulation of anions at the perovskite/spiro-OMeTAD interface, which also likely includes an electronic component. This interface is a dominant recombination pathway at lower voltages and can account for the large disparity in fill factors observed in PSCs. By developing detailed models for the IMPS response at both OC and short-circuit conditions, we also confirm that the arcs observed in the upper quadrant of the IMPS spectra are not related to transport times, as is commonly interpreted, but time constants results from the combination of the series resistance and capacitors within the circuit. By combining the insights from IMPS and IS measurements, we develop a more complete equivalent circuit for PSCs that can be used as a basis for further research with different perovskite materials and contact layers.