Resolving Complex Photoconductivity of Perovskite and Organic Semiconductor Films Using Phase-Sensitive Microwave Interferometry

Abstract

Complex transient photoconductivity (Δσ) contains rich fingerprints of charge recombination dynamics in photoactive films. However, a direct measure of both real (Δσ′) and imaginary (Δσ″) components has proven difficult using conventional cavity-based time-resolved microwave conductivity approaches. Here, we present a novel approach to resolve Δσ′ and Δσ″ parts of Δσ by using a nonresonant coplanar transmission line and a microwave interferometric detection scheme. The use of a phase-sensitive microwave interferometer greatly increases the measurement sensitivity and eliminates the requirement of a resonant cavity. This broadband detection scheme allows for direct measurement of Δσ. The relationship between the experimental phase shift and Δσ′ and Δσ″ components is decoded through an in situ electron spin resonance (ESR) measurement. ESR line shape analysis is used to confirm the assignment of the transients to the Δσ′ and Δσ″ components. We demonstrate the utility of this technique on thin films of poly(3-hexylthiophene): [6,6]-phenylC61-butyric acid methyl ester (P3HT:PCBM) and perovskite MA0.85FA0.15PbI3 films on glass.