Supercapacitors can be categorized into two main types; the electrochemical double layer capacitors (EDLL) and the pseudocapacitors. EDLL supercapacitors are very similar in principle to ordinary capacitors as they are formed of two parallel conducting plates with no charge transfer. Pseudocapacitors, on the other hand, depend on charge transfer mechanisms occurring on the electrodes (Ramesh et al., 2018). One main factor affecting the choice of a supercapacitor for a certain application is its life cycle, which is heavily affected and determined by the life cycle of the biopolymer composite used in the fabrication.

Photodiodes and Photovoltaic Solar Cells

Biopolymers received lots of attention in various fields of high-tech applications. Optoelectronics is a major field. In such a field, the electronic circuits of the optoelectronic systems operate electronics as well as optics not only to convert electronic signals into light and vice versa, but also for storing, transmitting, and further processing. The most widespread inorganic photodiodes are fabricated from gallium arsenide (GaAS). Photodiodes have many applications in several fields both of civilian and military nature.

In principle, a photovoltaic (PV) solar cell is a silicon-based multi-layer device used to convert light energy into electric energy. The fact that biopolymers like starch, cellulose, collagen, and many other widely available worldwide have repeated carboxyl, hydroxyl, and amino functional groups, gives them the ability to connect and interrelate with their surroundings. To get benefit out of the many advantages biocomposite polymers can offer to the industry of solar cells, recent research has been focusing on introducing new generations of organic solar cells. Biopolymers and nanoparticles are being used not only in the substrate part of the solar cells, but also within all other layers including the photoelectric layer, the dye, and electrolyte. Organic-based PV solar cells can be of a single-layer or a two-layer structure. In a single-layer cell, the two conduction electrodes are separated by the organic photosensitive electronic composite. On the other hand, to construct a two-layer cell, the photosensitive layer is formed out of two layers; one as an electron donor and the other as an electron acceptor. The illustrations presented in Figure 3.10 show the device structure, layout, and photonic efficiency versus bending cycles of the proposed device presented in (La Notte et al., 2018).

(A) 3D illustration of the organic photovoltaic

FIGURE 3.10 (A) 3D illustration of the organic photovoltaic. (B) OPV layout. (C) Image of the substrate under mechanical bending. (D) Performance characteristics the OPV under different degrees of binding. (Adapted from La Notte et ah. 2018.)

PLA is a thermoplastic polyester, which means that it can be heated to its melting point at around 150-160°C, cooled, and heated again without any degradation. In contrast, the thermoset plastic can be heated only once and it is irreversible. Due to its characteristics, PLA has been the most studied and utilized biodegradable plastic in human history. It is replacing conventional petrochemical-based polymers slowly and becoming the leading biomaterial for medical application as well as in other plastic industries.

Ultraviolet photodetectors are special types of photodiodes that are designed and fabricated to be used to detect and interact with the part of the electromagnetic wave spectrum with wave lengths within the range of 280-400 nm. Such light detectors found very important roles in a wide range of applications including environment monitoring, communications, and astronomy. ZnO-cellulose composite is one of the very attractive biocomposite materials that have been used in the fabrication of ultraviolet (UV) detectors (Mohiuddin et al., 2017). This is mainly because this biocomposite combines the very attractive features of both ZnO and cellulose. In this biocomposite, cellulose is used to form a flexible matrix for the ZnO active element. When exposed to oxygen, zinc oxide becomes sensitive to light. Cellulose fibers, on the other hand, are very absorbent, mechanically strong, and molecular oxygen can easily permeate through cellulose matrix. Photonic sensitivity of this composite is highly dependent on the ratio of ZnO to cellulose contents.

In the face of the various benefits they enjoy, biopolymer-based PV solar cells still have some drawbacks leading to real challenges to its industry. The poor light to electric energy conversion rates, in addition to the instability in the overall performance and comparatively short life cycle are among their weaknesses. However, biopolymer composites, particularly the nanocellulosic materials, are believed to have the capability of improving the characteristics of specific properties of PV solar cells as one of the most promising materials in this regard due to their outstanding mechanical properties, ease of adaptation, elevated aspect ratio, and low density.

Other Electrical Applications of Biopolymers

Biopolymer-based materials have found significant roles in high-tech components in various modern and advanced applications. This includes but is not limited to electromagnetic interference shielding materials, fuel cell fabrication, piezoelectric and thermoelectric materials, and microwave absorbers.

The key challenge in the fuel cell industry is to have stable materials at a wide range of operating temperatures with high efficiency as well as having extended lifetimes, while being eco-friendly, sustainable, and commercially available (AL-Oqla et al., 2014c; AL-Oqla & Sapuan, 2014b; AL-Oqla & Sapuan, 2018b). Chitosan and starch, cellulose, and chitin as well as other biomaterials are being considered as good candidates to be used in more economic and eco-friendly fuel cells.

Energy harvesting systems employing the piezoelectric principle as well as thermoelectric principle are imperative fields for the use of the notable properties of biopolymers (AL-Oqla et al., 2018). Biopolymers’ excellent flexibility makes them reasonable candidates as energy harvesting materials. They have the ability to change any applied mechanical stress into free electric charges regardless of the direction of the stress. Polyamides, liquid crystal polymers, and Parylene C are reported for their piezoelectricity. Examples of thermoelectric materials are PANI. PPY, and polythiophene (PTh) and its derivatives.

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