Project Details
Projekt
Stress and strain resisting polymer solar cells: Towards high flexibility
Subject Area
Polymer Materials
Term
since 2022
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 455748945
The stability of polymer solar cells, in which at least one component of the photoactive layer is a conjugated polymer, is often studied as a function of the illumination spectrum, temperature (cycles), humidity, and influence of reactants such as oxygen or water. In addition, attention is paid to long-term stable mixing of electron donors and acceptors, which is referred to the morphological stability. In particular for potential real applications, the flexible properties of organic solar modules are important, which, however, places increased demands on their mechanical stability.Due to the bending of solar modules that occurs during application, cracks in the active layer as well as detachment of the active layer from the charge extraction layers (or electrodes) can occur. The latter process is called delamination and it occurs when the adhesion between two layers is unsatisfactory, while cracks within a layer indicate insufficient cohesion. This project is, therefore, dedicated to the prevention of cracks and delamination defects, as well as to their healing. For this purpose, the material properties are specifically manipulated to obtain a higher mechanical resilience and to heal defects that have occurred.For mechanical resilience, approaches are pursued which reduce the crystallinity of the photoactive layer, stabilize the interfaces between donor and acceptor as well as those to the charge extraction layers with the aid of additives, and improve their mechanical resilience by entanglements of polymers. For the healing approach, the mobility of the materials is increased, so that an increased temperature and, if required, additional pressure lead to vacancies caused by cracks and delaminations being filled with material again, restoring the function of the solar cell. However, care is taken to ensure that the mixture morphology is either stabilized by interfacially active components or restored by reforming. The material systems are based on the donor / acceptor materials provided by a different project or on classical poly(3-alkylthiophenes) in combination with fullerene derivatives and later also non-fullerene acceptors.The photoactive layer also consists of at least ternary mixtures to be able to map the required properties. To investigate healing, films and solar cells on flexible substrates are stretched or bent, respectively, to provoke cracking and delamination. The defects created by the mechanical stress are characterized and quantified by microscopic and spectroscopic methods. After the healing, an analogous procedure is performed enabling a quantification of the healing.
DFG Programme
Research Units
