Temperature effects in oxidative molecular layer deposition (oMLD) of polypyrrole

Polypyrrole (pPy) is a promising conductive polymer, yet its electrochemical performance and structural stability strongly depend on synthesis conditions. Recent work has demonstrated enhanced charge capacity in pPy films formed by oxidative molecular layer deposition (oMLD) at 150 °C; however, lower growth temperatures are of interest to enhance the oMLD growth rate. Here, we investigate how lower growth temperatures spanning 100–150 °C impact the growth rate, structure, and properties of pPy thin films. In situ quartz crystal microbalance (QCM) revealed that lower growth temperatures yield higher mass gain per cycle but lead to nonuniform growth and incorporation of residual by-products. X-ray photoelectron spectroscopy, scanning electron microscopy, differential scanning calorimetry, and thermogravimetric analysis confirmed that films deposited at elevated temperatures exhibit cleaner chemistry, smoother morphology, and exceptional thermal stability, with negligible mass loss up to 600 °C. Electrochemical analysis demonstrated that films formed at higher temperatures deliver higher specific capacity (up to 343 mA h/g at steady state) and improved cycling stability compared to low-temperature films. All films retained their electrochemical properties following postdeposition vacuum anneal at 250 °C, while heating to 50 °C during cyclic voltammetry measurements boosted charge capacity and stability. These findings establish growth temperature as a key parameter for tailoring pPy properties and demonstrate that oMLD pPy grown at 150 °C can produce structurally and electrochemically robust films for next-generation energy storage and electronic applications.