Modifications and multiple roles of graphene film in SIS structural solar cells

• Published in: Solar energy 2015-12, Vol.122, p.658-666
• Main Authors: Chen, S.M., Gao, M., Fang, X.H., Ma, Z.Q.
• Format: Article
• Language: English
• Subjects: Chemical vapor deposition; Energy efficiency; Fermi pinning effect; Graphene film; Interface states; Modification roles; Oxidation; Photovoltaic cells; Solar cell structure; Solar energy; Transmission electron microscopy
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/j.solener.2015.09.039

•Large area and high-quality graphene films were synthesized by CVD technique.•The idea of inserting graphene film in traditional SIS structures has some novelty.•A relatively high efficiency is obtained with the unusual structure of solar cell.•The modification roles on carrier transport of graphene film were discussed.•The action ways of interfacial ultrathin oxide layer were testified. In this report, large area and high-quality graphene films were synthesized under 1000°C by chemical vapor deposition technique. Their structure, optical and electronic properties have been characterized by Raman spectroscopy, Ultraviolet–visible spectrophotometry and Hall Effect measurement system, respectively. The films were found to be perfect sp2 bonding form of graphene with a maximum size of 9cm2. By contrasting the current–voltage feature of ITO/SiOx/Si, G/ITO/SiOx/Si and ITO/G/SiOx/Si configurations, the different roles of graphene layer to the heterojunction solar cells were discussed. The results showed that an energy conversion efficiency of 7.54% is obtained with the structure of G/ITO/SiOx/Si. The improved solar cell performance was attributed to the roles of graphene in SIS structures, such as improvement of light transmission and current flow, reduction of interfacial states and removal of Fermi pinning effect at the hetero-junctions between graphene films and oxides. The interfacial region between ITO, Graphene and Silicon was analyzed by transmission electron microscope image and X-ray photoelectron spectroscopy. It was found that the a-SiOx layer does exist between ITO film and Si substrate even without intentional oxidation treatment. The surface passivation and defect-assisted tunneling effect of the ultra-thin oxide layers was reflected by the device performance.