## 1 Introduction
CPs can be dissolved in eco-friendly solvents like water, commonly used in the case of poly(3,_A_-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). Another interesting approach is to perform the in-situ polymerization, which enables to polymerize onto the cellulose fibers [16]. The source of cellulose is important, as it could have different interactions with solvent and CPs, and in consequence different properties, such as its flexibility and conductivity [17]. Despite the insulating behavior of cellulosic substrates, it has been shown that conjugated polymer-cellulose composite electrode materials feature high capacitances and conductivity and low sheet resistances [18]. Recently, [PERSON] and co-workers reported the use of cellulose nanofibers as building blocks on the fabrication of nanostructured PEDOT flexible paper [16]. The research group has described a versatile solution for the development of highly conductive and flexible nanocellulose fibers coated with nanostructured PEDOT within 30 min leading to a material with a large surface area, low sheet resistance, and high active mass loading (7.3 mg\(\cdot\)cm\({}^{-2}\)) and high specific electrode capacitances (0.92 F\(\cdot\)cm\({}^{-2}\)). The relationship between conductive properties and surface topography of cellulose composite materials is a fundamental issue as surface properties may have a fundamental impact on the performance of paper-based supercapacitors [14]. However, to characterize this relationship is not always an easy task as difficulties are reported with the measuring of similar materials with AFM due to the non-uniform geometrical structure and size of cellulose fibers [19]. In this work, we describe a straightforward, fast and versatile solution-based approach for the fabrication of robust, conductive and highly flexible PEDOT paper. Within our research group, we have already developed a methodology for the preparation of highly luminescent and superhydrophobic polyfluorene/silica/cellulose hybrid materials. These multifunctional, versatile, and easily processed and scalable hybrid materials are suitable for large surfaces and industrial applications [20; 21]. To our knowledge, surface properties of CP-cellulose materials have not been studied with 3D optical profilometry. Among other advantages, 3D optical profilometry allows to obtain fast 3D real-color imaging with a vertical and lateral resolution more adequate to characterize cellulose microfibers composite materials than AFM. We present the process for obtaining conductive paper by casting or spray coating different thiophene-derived polymers as PEDOT and a soluble in organic solvents alkylated PProDOT. Moreover, we study the effect of different substrates (filter conventional paper, cellulose acetate and isolated cellulose microfibers) on the free-standing PEDOT structure employing different processing methodologies that were used for polythiophenes-derivative polymers deposition of conducting papers. Towards a better understanding of properties and interactions between cellulose and CPs, thermal stability, infrared spectroscopy, scanning electron microscopy, electrical conductivity, and surface 3D optical profilometry have been carried out. Composite materials were evaluated in terms of electrical conductivity and surface roughness, obtaining a dependence of the electrical properties with the surface morphology and processing conditions (solvent and nature of the substrate). Regardless the surface roughness of the cellulosic substrate, it is possible to produce flexible composite materials with good conductive properties through in-situ approach in short times.