ED Sciences Physiques et de l'Ingénieur
Toward fully printed stabled Organic solar cells
by Rébecca DAMAMME (Laboratoire de l'Intégration du Matériau au Système)
The defense will take place at 9h30 - Amphithéâtre 3 16 Avenue Pey-Berland, ENSMAC, 33600 Pessac
in front of the jury composed of
- Guillaume WANTZ - Professeur des universités - Bordeaux INP - Directeur de these
- Cyril AUMAITRE - Chargé de recherche - CEA Grenoble - Rapporteur
- Damien THUAU - Maître de conférences - Bordeaux INP - CoDirecteur de these
- Ellen MOONS - Full professor - Université de Karlstad - Rapporteur
- Trystan WATSON - Full professor - Université de Swansea - Examinateur
- Aline ROUGIER - Directrice de recherche - CNRS / Université de Bordeaux - Examinateur
Organic solar cells (OSCs) are part of an emerging photovoltaic technology characterized by low-temperature fabrication processes, a solution-based approach that enables large-scale printing, mechanical flexibility, and low weight. These properties enable applications that are inaccessible to established inorganic technologies, including building-integrated photovoltaics, agrivoltaics, and portable devices. While power conversion efficiencies (PCE) in the laboratory now exceed 20% on scales smaller than square centimeters thanks to non-fullerene acceptors (NFAs), a significant gap remains compared to performance achieved on an industrial scale (5-6% for the best commercial modules). This gap reflects two major and closely related challenges: on the one hand, the still-limited stability of OSCs under real-word operating conditions, and on the other hand, scaling difficulties, whether related to the transfer of deposition processes or to performance losses observed when scaling-up to modules with larger surface areas. The objective of this thesis is to bridge this “lab-to-fab” gap by addressing these challenges through three complementary approaches. The first section (Chapter 2) aims to establish guidelines for the design and selection of materials for the active layer that are both high-performing and stable. Using a multiscale approach that combines UV-vis and infrared spectroscopy, X-ray diffraction (GIWAXS), and measurements on complete devices, this chapter characterizes the sensitivity to photooxidation of organic donor (PM6, PTQ10) and acceptor (Y6-12) semiconductors, both individually and in blends, and highlights the role of crystallinity – controlled by thermal annealing – in balancing photovoltaic performance and stability. The addition of a third component, PC71BM, which acts as a radical scavenger, is then shown to be an additional lever for improving performance retention during aging. These results guide the selection of the PTQ10:Y6-12:PC71BM system as the reference for the remainder of the thesis. The second focus area (Chapter 3) concerns the transfer of this system to printable deposition processes compatible with industrial manufacturing. A zinc-chelated PEI (PEI-Zn)-based electron transport layer is being developed and studied as a low-temperature alternative to sol-gel ZnO, and printable hole transport layers are being evaluated and optimized. The transition from spin coating to blade coating, and then to slot-die coating, enables efficiencies exceeding 11% the be achieved on devices that are almost entirely printed. The third focus point (Chapter 4) addresses the scaling of the active surface area, the main bottleneck identified between the laboratory device and the module. A combination of experimental characterizations, finite element simulations (COMSOL), and electrode geometry engineering allows the series resistance to be identified as the primary limiting mechanism. A new electrode design, combining a widened charge-collecting busbar with the removal of a resistive bottleneck, yields a efficiency gain of approximately 2.3 percentage points across all the surfaces studied. Together, these results establish structure-stability-process relationships and propose concrete solutions for bringing the performance of laboratory-scale organic photovoltaics closer to that required for industrial deployment.