A transparent conductor is a relevant constituent in several photoelectronic appliances. Indium tin oxide (ITO) is principally used for fabricating transparent conductors due to its properties [1]. Nevertheless, ITO has many disadvantages; for instance, it is expensive and it does not find application in flexible devices because of its brittle nature [2]. Consequently, consideration in the semiconductor field has been drawn to graphene [3], which shows broadband light absorption, linear dispersion band structure and an ultrahigh charge-carrier mobility. Graphene-based materials are thus advantageous materials that can be produced in ultrathin sheet form and may be used in several applications [4,5,6,7,8,9,10,11].

Chemical vapor deposition (CVD) is a technique used for high-quality graphene production [12]. The employment of CVD technology in ultradense photonic, optoelectronic, and electronic instruments has been reported [13,14,15].

Graphene oxide (GO) is a graphene-based material that has more oxygen-containing groups and defects in comparison with mechanically exfoliated or CVD-grown graphene. These defects are advantageous to enhance the performance of photodetectors [16]. Additionally, GO thin films show high optical transmittance in the visible region that allows their use as protective coatings and optically transparent electrodes, crucial in solar cells and for optical applications [17].

GO reduction is a method for large scale graphene manufacturing [18]. Reduced graphene oxide (RGO) is achieved using chemical methods [19], which eliminate or diminish the oxygen-containing groups. Additional reduction methods are thermal annealing that should be carried out above 200 °C [20] and “green reducers” (for instance vitamin C) [21].

RGO can be functionalized with Poly(Sodium 4-Styrenesulfonate) (PSS), which is a polyelectrolyte that avoids RGO aggregation. PSS interacts with graphene by means of π-π interactions, is soluble in water and safe to use [22].

Presently graphene nanoplatelets (GNPs) have arisen as a new graphene-based material. GNPs show some of the beneficial properties of single layer graphene [23]. GNPs are composed of mono- to few-layer sheets of sp² bonded carbon atoms that overlap creating nanometers thick 2D particles [24]. They can be obtained by means of exfoliation of cheap graphite flakes and then through chemical oxidation and graphite oxide nanoplatelets reduction [24].

Graphene-based materials show notable optical properties such as highly transparency in visible spectrum, photo-response up to Terahertz frequency range and tunable infrared optical absorbance [25].

Spectroscopic Ellipsometry (SE) [26] is an highly precise optical method designed for studying the optical properties of materials.

SE has been extensively used to study graphene-based films. The complex refractive index of monolayer graphene has been investigated using SE [25,27,28]. In Ref. [29] the optical constants of graphene were studied by means of a phenomenological Fano model. The optical properties of thick as well as few-layer GO and RGO were studied using SE [30,31].

We present a review of the authors’ research works on Variable-Angle Spectroscopy (VASE) of graphene-based films [32,33,34,35,36,37,38,39].

Despite the availability of literature on SE of graphene-based materials [40], there are not reviews about the optical interaction of GO with magnetron-sputtered metals studied using VASE, which is a promising research area. Moreover, we report about VASE optical model of less studied graphene-based materials such as GNPs and RGO stabilized with PSS films; particular attention to CVD-grown graphene on flexible substrates is given.

3. Conclusions and Outlook