Fabrication of Electronic Devices Using Highly Flexible Microfibrillated Cellulose

Cellulose, as the most abundant biopolymer in the world and the main component of  papers, is a polysaccharide consisting of thousands of β -linked glucose unit. The hydroxyl groups on the backbone of cellulose make it easy to be functionalized. In the meanwhile, modern technology requires electronic devices to be more flexible and environmental friendly, which makes cellulose to be a candidate to fabricate electronic devices. Up to now, lots of researches employ “paper-like” plastic polymers to fabricate electronics rather than using real cellulose paper. Cellulose, compared to its counterparts, is much cheaper, more environmental-friendly and has the excellent properties of being flexible and mechanically strong. There are also some general challenges about using cellulose for electronics, such as its nonconductivity, porosity and roughness, but these features can be taken advantages of on some occasions. In my study, two different cellulose based electronic devices will be studied. For the first part, an ionic paper-based diode(IPD) was made by combining together two oppositely charged microfibrillated cellulose sublayers. Unlike the conventional p-n junctions using electrons and holes as charge carriers, the IPD relies on transportation of ions to conduct current. The asymmetric charge distribution between the two sublayers will help selectively transport cations and anions under positive and negative bias, to allow an electric current to pass in only one direction. For the second part, flexible and free-standing supercapacitors made mainly by muti-walled carbon nanotubes(CNTs) and micro-fabrillated cellulose(MFC) was investigated. The results indicated that the as-made supercapacitor showed a high specific capacitance of 176mF/cm². In addition, the electrochemical properties of the supercapacitors remained almost the same under severe bending. In sum, cellulose-based electronics have good characteristics of being low-cost, green and flexible and can be applied in various areas, such as supercapacitors, transistor, solar cells, etc.