Nanotechnology Solar Cell Applications – Graphene-Based Materials

By Michael Berger. Copyright © Nanowerk

(Nanowerk Spotlight) Graphene-based nanomaterials have  many promising applications in energy-related areas. In particular, there are  four major energy-related areas where graphene will have an impact: solar cells,  supercapacitors, lithium-ion batteries, and catalysis for fuel cells (read more:  “Graphene-based  nanotechnology in energy applications”).

 

 

The extremely high electron mobility of graphene – under ideal  conditions electrons move through it with roughly 100 times the mobility they  have in silicon – combined with its superior strength and the fact that it is  nearly transparent (2.3 % of light is absorbed; 97.7 % transmitted), make it an  ideal candidate for photovoltaic applications. It could be a promising  replacement material for indium tin oxide (ITO), the current standard material  for transparent electrodes used for electrodes in LCD displays, solar cells,  iPad and smart-phone touch screens, and organic light-emitting diode (OLED)  displays for televisions and computer monitors.

Just yesterday, for instance, there was a report (“Nanotechnology  researchers make major leap towards graphene for solar cells”) that shows  that graphene retains its impressive set of properties when it is coated with a  thin silicon film. These findings pave the way for entirely new possibilities to  use in thin-film photovoltaics.

A new review in Advanced Energy Materials (“Graphene-Based Materials for Solar Cell  Applications”) by a team of scientists from Nanyang Technological  University, led by Prof. Hua Zhang, provides an overview of the recent  research on graphene and its derivatives, with a particular focus on synthesis,  properties, and applications in solar cells.

 

Schematic representation of the energy level alignment (top) and the  construction of heterojunction organic solar cell fabricated with graphene as  anodic electrode: graphene/PEDOT/CuPc/C60/BCP/Al.  (©Wiley-VCH Verlag)  

With the unique properties, i.e., highly optical transparence,  highly electrical conduction, and mechanical flexibility, graphene and its  derivatives have been investigated extensively in the field of solar cells. The review looks in detail at some of the impressive results  that have been reported where graphene was used as the electrodes, i.e.:

• –transparent  anodes
• –non-transparent  anodes
• –transparent  cathodes
• –catalytic  counter electrodes

as well as where graphene was used as the active layer, i.e.:

• –light  harvesting material
• –Schottky  junction
• –electron  transport layer
• –hole  transport layer
• –both  hole and electron transport layer
• –and  interfacial layer in the tandem configuration.

Summing up their review, the authors conclude that it is  promising that graphene, as the transparent electrode material, has exhibited  superiority in that it is highly flexible, an abundant carbon source, and has  high thermal/chemical stability, compared to the traditional ITO. In particular,  the flexible transparent electrodes show applications not only in solar cells,  but also in flexible touch screens, displays, printable electronics, flexible  transistors, memories, etc.

Schematic illustration of the transfer process of CVD-graphene onto  transparent substrate. (©Wiley-VCH Verlag)  

 

“In addition to working as transparent electrodes, graphene,  graphene oxide (GO), and their derivatives show many other important  applications that include being electron/hole transporters and serving as  interfacial layers and Schottky junction layers in photovoltaics devices,” write  the authors. “Two-dimensional (2D) graphene oxide is capable of π-π stacking and  hydrogen bonding. This makes it possible to use such a 2D scaffold as the  template to self-assemble GO-based novel inorganic, organic, and  inorganic-organic hybrids with multifunctionalities for applications in  photovoltaics.”

“On the other hand, to enrich the application of graphene,  processes on bandgap opening have always attracted the attention of scientists.  To date, many methods have been investigated to engineer the band structure of  graphene, including inducing a quantum confinement effect by reduction of  graphene lateral size to form nanoribbons or nanomesh introducing foreign  elements, and employing a strain effect from the substrate.

 

We believe that  graphene will play more and more important roles in solar cells and other  fields, such as energy storage, optoelectronics, electrics and sensing, in the  near future.”
Read more: http://www.nanowerk.com/spotlight/spotid=32691.php#ixzz2i7UENfhw