Electrochemically synthesized polythiophene molecules: Effect of layer thickness on electrochromic performance and photocurrent response

Abstract

This study presents a comprehensive analysis of the electrochemical and electrochromic properties of polythiophene thin films, synthesized electrochemically on ITO-coated glass substrates. PTH200, PTH300, PTH400, and PTH500 refer to the films produced at deposition times of 200, 300, 400, and 500 s, respectively. The study also examines the effect of film thickness on response time, optical modulation, reversibility, and coloration efficiency. Structural and morphological characteristics are thoroughly analyzed using FTIR, Raman spectroscopy, and FESEM. The molecular formation of the polythiophene is confirmed by FTIR and Raman spectroscopy. A variety of techniques, such as cyclic voltammetry, chronoamperometry (CA), chronocoulometry (CC), and electrochemical impedance spectroscopy (EIS), are used to evaluate the performance of electrochromic films. The coloration and bleaching times for the films are 5.2/3.7 s, 12.1/4.4 s, 7.0/1.7 s, and 4.9/1.1 s for PTH200, PTH300, PTH400, and PTH500, respectively. PTH500 exhibits superior electrochromic performance compared to the other polythiophene films, with a high optical contrast of 49.1 %, a coloration efficiency of 343.4 cm2 C-1, and a reversibility of 79.8 %. Linear sweep voltammetry measurements using a three-electrode cell configuration reveal that all PTH films show an enhanced photocurrent response under solar illumination. The insightful findings from EIS studies demonstrate that both capacitive and resistive elements play a vital role in controlling the charge transfer mechanism. The PTH500 film exhibits the lowest charge transfer resistance, which supports its superior electrochromic performance. This investigation highlights the impact of varying film thicknesses on electrochromic properties and redox activity, providing valuable insights for future research in this field.