Abstract
New architectures of transparent conductive electrodes (TCEs) incorporating graphene monolayers in different configurations have been explored with the aim to improve the performance of silicon-heterojunction (SHJ) cell front transparent contacts. In SHJ technology, front electrodes play an important additional role as anti-reflectance (AR) coatings. In this work, different transparent-conductive-oxide (TCO) thin films have been combined with graphene monolayers in different configurations, yielding advanced transparent electrodes specifically designed to minimize surface reflection over a wide range of wavelengths and angles of incidence and to improve electrical performance. A preliminary analysis reveals a strong dependence of the optoelectronic properties of the TCEs on (i) the order in which the different thin films are deposited or the graphene is transferred and (ii) the specific TCO material used. The results shows a clear electrical improvement when three graphene monolayers are placed on top on 80-nm-thick ITO thin film. This optimum TCE presents sheet resistances as low as 55 Ω/sq and an average conductance as high as 13.12 mS. In addition, the spectral reflectance of this TCE also shows an important reduction in its weighted reflectance value of 2–3%. Hence, the work undergone so far clearly suggests the possibility to noticeably improve transparent electrodes with this approach and therefore to further enhance silicon-heterojunction cell performance. These results achieved so far clearly open the possibility to noticeably improve TCEs and therefore to further enhance SHJ contact-technology performance.
Highlights
Graphene has been regarded as a promising candidate for the new emerging generation of transparent electrodes in several applications such as displays, touch screens and/or solar cells [1,2]
The evaluation of transparent conductive electrodes (TCEs) made by coating the graphene monolayers (GML) with a sputtered TCO layer indicated that this process severely affected the structure of graphene, leading to a significant detriment of sheet-resistance
The GML placed on top of a TCO led to TCEs with relatively good sheet resistances, when the TCO material was indium tin oxide (ITO)
Summary
Graphene has been regarded as a promising candidate for the new emerging generation of transparent electrodes in several applications such as displays, touch screens and/or solar cells [1,2]. One of the main application areas of transparent electrodes is photovoltaics (PV) and graphene possesses most, if not all of the properties required for it to offer innovative solutions in the field: high optical transmittance, exceptional electronic transport, outstanding mechanical strength and environmental stability [6]. Significant effort has been devoted to improve the overall performance of PV devices using graphene. This material has been reported to play diverse positive roles acting as electrode, active layer, interfacial layer or electron acceptor in photovoltaic cells [7,8,9,10,11,12]. Research on solar cells containing graphene in their structure is still at laboratory scale, owing to both a lack in the ability to produce large-sized graphene sheets and a relatively low reproducibility of its properties
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