Quantitative Transient Absorption Measurements of Polaron Yield and Absorption Coefficient in Neat Conjugated Polymers

Transient absorption methods are crucial for probing photogenerated polaron dynamics in conjugated polymers but are usually limited to qualitative studies because the polaron absorption coefficient is unknown. Herein, we quantify polaron absorption coefficients by exploiting the parasitic exciton-polaron quenching process, which appears in transient absorption experiments as a decrease in polaron yield at high fluence. We modulate the charge density in neat polymer films and measure the exciton-polaron quenching rate constant and dopant density via time-resolved photoluminescence. Using these parameters, we fit relative yield-fluence curves obtained from transient absorption, quantifying the yield and absorption coefficient of the polarons. We use time-resolved microwave conductivity as the transient probe and present results for the GHz mobility and polaron yield in films of three common conjugated polymers that are consistent with previous reports where they exist. These experiments demonstrate a new, generally accessible spectroscopic method for quantitative study of polaron dynamics in conjugated polymers.