Development of PEDOT:PSS-based transparent electrode for high-performance stretchable organic solar cells

Abstract

Stretchable organic solar cells (SOSCs) have emerged as a promising alternative to conventional silicon solar cells for powering wearable electronic devices due to their lightweight, flexibility, and affordability. The development of high-performance SOSCs critically depends on the design of transparent electrodes that can efficiently conduct electricity and allow light to pass through the cell. Currently, Indium Tin Oxide (ITO) is the most widely used material for transparent electrodes in OSCs. However, ITO has drawbacks such as fragility, high cost, and limited versatility. Consequently, there is a growing interest in exploring alternative materials that can replace ITO for realizing stretchable organic solar cells. Among the alternative materials, Poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT:PSS) has been extensively investigated as a transparent electrode in stretchable OSC research due to its high electrical conductivity, excellent transparency, and low cost. However, the inherent mechanical instability of PEDOT:PSS limits its application as a stretchable solar cell, which is essential for various wearable and stretchable electronic devices. This paper aims to develop a transparent electrode based on PEDOT:PSS that can maintain high electrical conductivity and excellent transparency under mechanical deformation. In Chapter 1, an introduction is provided on the basic principles of organic solar cells, the classification of stretchable organic solar cells, and the previous research on improving the mechanical and electrical properties of PEDOT:PSS for its application as a stretchable transparent electrode. Chapter 2 presents a study focused on addressing the issue of conductivity reduction caused by excessive aggregation due to the commonly used cross-linking agent 3-Glycidoxypropyltrimethoxysilane (GOPS) in order to enhance the mechanical properties of PEDOT:PSS. This research achieves improved conductivity and stretchability in organic solar cells by controlling the number of alkoxysilane functional groups and introducing flexible molecules to reduce the aggregation of silane. In Chapter 3, a method utilizing acid treatment is explained to enhance the optical and electrical properties of PEDOT:PSS electrodes. By forming a diffusion interface between the mechanically weak acid-treated PEDOT:PSS electrode and the TPU substrate, an electrode with improved adhesion and stretchability is developed. This resulted in the successful development of highly efficient (PCE: ~13%) and stretchable ($PCE_{80%}$ = 34%) organic solar cells. The successful development of high-performance PEDOT:PSS-based transparent electrodes for stretchable OSCs not only enhances the performance and reliability of OSCs but also enables the development of various wearable and stretchable electronic components. This research is expected to contribute to the advancement of flexible and stretchable electronic devices and the realization of sustainable and clean energy production.