Although fossil-fuel emissions may be the poster child for global warming, there is also growing concern over environmental harm from discarded electronics.
Researchers at Georgia Tech’s Center for Organic Photonics and Electronics (COPE) and Renewable Bioproducts Institute are developing paper-based electronics — organic solar cells, organic light-emitting diodes (OLEDs), and organic field-effect transistors (OFETs) — fabricated on cellulose-based substrates that can be recycled easily.
Use of paper for substrates has generated considerable buzz among researchers, but its high porosity and surface roughness pose challenges. Today’s organic electronic components use very thin carbon-based semiconductor layers — about 1,000 times thinner than the average human hair. “Because they are so thin, you need nearly atomically flat substrates where the surface is down to a nanometer,” explained Bernard Kippelen, director of COPE and a professor in Georgia Tech’s School of Electrical and Computer Engineering.
To address this, Kippelen’s team is using cellulose nanocrystals (CNCs), a type of wooden wunderkind material, to develop new semiconductor devices, demonstrating that CNCs are a viable alternative to traditional plastic substrates — while offering new environmental benefits. Devices made on these substrates can be easily dissolved in water, allowing semiconducting materials and metal layers to be filtered and recycled.
Applications will depend on economics and performance. For CNC-based solar cells, the researchers have achieved power conversion efficiencies of 4 percent. Efficiencies could be increased to 10 percent but would require more expensive materials, Kippelen said. So instead of paper-based solar farms becoming the norm, he predicts low-power applications, such as computer covers and mousepads, for CNC-based solar cells.
Cellulose-based OLEDs, which have performance comparable with current devices, show greater potential for market adoption. “The trend in flat-panel displays is larger size and higher resolution,” Kippelen said. “Glass substrates, however, pose manufacturing and transportation problems because of their rigidity and breakability. And plastic has problems at the end-of-product lifecycle.”
Yet with the low cost and flexibility of paper-based OLEDs, flat panel displays could be the size of a wall.
Read the entire article in the latest issue of Horizon magazine.