Impact of poly-3-hexylthiophene active layer thickness for smart window applications

Poly(3-hexylthiophene) (P3HT) is a semiconducting conjugated polymer also known for its electrochromic (EC) properties, i.e., change in color in response to the application of a cyclic change of electric voltage. This property makes it a promising candidate for various applications, including smart windows, displays, and sensors. Here, we are reporting the thickness-dependent EC response of spin-coated P3HT films. The emphasis is to probe the effect of the layer thickness on structural disordering/distortion and their synergetic role on EC performance of the as-prepared P3HT devices. The relationship between the P3HT film layer thicknesses on EC device performance has to be understood based on structural morphology and its microscopic ordering. In spin-coated films like P3HT, thicker layers have greater structural disorder and higher defect density. This disorder can disrupt the long-range conjugation and charge transport pathways, thereby affecting key performance metrics of the devices. For this EC study, P3HT thin films were deposited onto ITO-coated glass substrates through the spin coating method with different spin speeds ranging from 500 rpm to 2000 rpm. XRD analysis showed peak broadening for (001) pc and (002) pc planes with increasing thickness of the films, which depicted the geometrical distortion. UV-vis. Spectra showed a slight variation in the optical band structure with increasing thickness. The cyclic voltammetry (CV) study showed a reversible change in color (Purple – transparent – Purple) with the application of cyclic voltage ranging from −1 V to + 1 V. It is observed that the film with a lower thickness (∼ 300 nm) exhibited a better electrochemical reversibility than the thicker films. The findings made here have great implications for understanding the EC characteristics parameters, such as activation voltage, maximum current, and optical contrast, as they are subjected to the film thickness. Moreover, comprehending this behaviour is essential for tailoring P3HT-based devices for specific applications. • The impact of film thickness on structural and microstructural is studied. • Impact of film thickness on optoelectronic properties were investigated. • All studied systems showed color reversibility from purple to transparent. • The thinner most film showed better electrochemical reversibility. • All films showed a highly stable reversible switching for CV-hysteresis.