Interfaces in organic photovoltaic devices: understanding the degradation mechanisms and improvement of the stability
Résumé
Organic photovoltaic (OPV) devices now regularly reach 10% power conversion efficiency, especially now with the development of non-fullerene acceptors. However, those performances are not always very stable and, in order to improve the lifetime of these devices, a deep understanding of the different degradation mechanisms is needed. Degradation pathways are complex and diverse: they can be induced by numerous intrinsic and extrinsic factors which can affect different regions of the device (active materials, interfaces, morphology, etc…).
In the first part of this presentation, I will specifically focus on the degradation occurring at different interfaces in the multilayer which forms the OPV device. We identified several degradation mechanisms occurring at the bottom interface (ETL/Active layer) as well as at the top interfaces (Active layer/HTL/Electrode).
In a second part, we studied the potentiality of graftable molecules such as self-assembled monolayers (SAM) to improve the stability of OPV devices. A solution to replace PEDOT:PSS in direct architecture was developed involving a thin layer of P3HT grafted on the ITO.
These different studies highlight the role of the architecture and, more specifically, of the ETL, HTL and electrode in the stability of OPV devices. They also showed that functionalization of the metal oxides can be a solution to improve the stability of the devices.