Chitosan in dye-sensitized solar cells

Biopolymers such as chitosan are attracting increasing attention as polymer electrolytes in dye-sensitized solar cells. Since chitosan has a low electrical conductivity, the study presented here aims to improve this by using salts and plasticizers.

 

Dye-sensitized solar cell based on a biopolymer electrolyte with chitosan

Majumdar, Simantini & Mondal, Archita & Mahajan, Ankita & Bhattacharya, Swapan & Ray, Ruma. (2023). Dye-sensitized solar cell employing chitosan-based biopolymer electrolyte. IOP Conference Series: Materials Science and Engineering. 1291. 012014. doi: 10.1088/1757-899X/1291/1/012014

Due to the global consumption of fossil fuels and increasing environmental pollution, green, sustainable and highly efficient carriers for storing and converting electrical energy are needed.

Dye-sensitive solar cells (DSSCs for short) are of interest here. DSSCs are photovoltaic cells that use a dye to convert visible light into electrical energy. DSSCs basically consist of a nanocrystalline semiconductor film with a wide band gap, a ruthenium dye complex, a transparent conductive semiconductor electrode, a redox pair electrolyte, e.g. I-/I₃^- , and a counter electrode. When the dye is excited in visible light, an electron is released and transferred to the counter electrode via the conductive glass substrate to reduce I₃^- to I^-. I^- is in turn used to fill the resulting electron gap on the dye. Overall, DSSCs have the advantage of low manufacturing costs and a simpler structure compared to conventional silicone-based photovoltaic devices.

The use of polymer electrolytes in DSSCs is becoming increasingly popular due to their good electrochemical properties and improved safety. Biopolymers such as starch, cellulose or chitosan are particularly interesting due to their good biodegradability, non-toxic properties, cost efficiency and availability. Chitosan is in focus due to its polar hydroxyl and amine groups, but suffers from low electrical conductivity. However, this can be improved by adding ionic salts and plasticizers such as lithium perchlorate (LiClO₄) and ethylene carbonate.

The aim of the following study is to improve the conductivity and electron transport properties of a chitosan-based biopolymer electrolyte with different concentrations of lithium perchlorate (LiClO₄) and ethylene carbonate. For this purpose, a dye-sensitized solar cell (DSSC) with zinc oxide (ZnO) nanoparticles as semiconductor material, Rose Bengal (RB) dye as photosensitive substance and a chitosan-based biopolymer electrolyte is constructed, characterized and energy conversion efficiency is estimated.

RESULTS

• Successful synthesis of ZnO nanoparticles with a size of 58 nm and a band gap of 3.32 eV
• Ionic conductivity of the biopolymer electrolyte increases with increasing LiClO4 concentration → highest at 80 % wt (~10^-5 S/cm), LiClO₄ plays a significant role in increasing conductivity
• Further improved by adding ethylene carbonate→ 45 % wt highest (~10^-4 S/cm), then decrease in ionic conductivity
• Analysis of the electron transport properties using Raman spectroscopy → maximum mobility and maximum number of charge carriers at 80 % wt LiClO₄ and 45 % wt ethylene carbonate
• Detection of the photovoltaic activity of the DSSC using linear scanning voltammetry

Conclusions: The addition of ionic salts and plasticizers can improve the electrical conductivity of chitosan as a polymer electrolyte. In addition, photovoltaic activity was demonstrated in the DSSC produced.

Link to article: https://iopscience.iop.org/article/10.1088/1757-899X/1291/1/012014