The ChemSta project will address the long-term stability of the perovskite films, first by working on the PPSs composition and chemistry to reach outstanding stabilization of the PSC absorber layers while keeping high efficiency. Its ambition is to prepare high efficiency PSC minimodules passing demanding stability qualification tests.

Photovoltaics (PV) still need improvement for cost-effectiveness, saving on raw material and cutting in pay-back energy consumption. Solid state perovskite solar cells (PSCs), the latest discovered PV technology, have made an unprecedented emergence as particularly promising high-performance devices. They now approach the best performances of single-crystalline silicon solar cells. However, presently, the bottleneck for the wide deployment of this technology is concerns about their stability and their sensitivity to external stressing factors, especially to moisture, oxygen and heat. The preparation of highly stable and efficient PSCs, that withstand demanding stability tests, remains the main challenge for the future of this technology. The ChemSta project aims at working at the heart of the PSC system that is the perovskite layer. A great strength of PSCs is that most of their functional layers, particularly the perovskite (PVK) photo-absorber film, are prepared at mild temperature (≤160°C) from solutions. Perovskite precursor solution (PPS) chemistry is key for the final properties of the absorber film. In these solutions, two kinds of components are added: (i) the elements and compounds that will form the film and (ii) those that will be eliminated during the synthesis, especially upon the final layer-annealing step. By working on this chemistry and on the crystallization control, we will dramatically increase the stability of the material and corresponding thin films, not only via intrinsic entropic stabilization, but also by enlarging the grain size, enhancing the crystallinity, suppressing defect formation, and stabilizing grain boundaries. For this, ChemSta will develop advanced and new approaches discovered by the coordinator’s group based on the synergy of additives and non-stoichiometry in the PPS.

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We are preparing highly stable 3D, quasi-2D Ruddlesden-Popper and quasi-2D Dion-Jacobson perovskite films by developing ad hoc chemistries and processings. The films are employed in encapsulated mini-modules.

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Methylammonium-free and bromide-free 3D-PVK films will be prepared using chlorides additive mixtures acting synergistically to obtain large grains, well-crystallized, pure phase and defect-free thin films. The composition will be adjusted to maximize entropic stabilization. Moreover, surface treatments will be applied and optimized to further stabilize the systems. Quasi-2D Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) formamidinium-based phases will also be developed by the new NS&A (non-stoichiometry and additive) approach. The role of non-stoichiometry will be studied in-depth as well as the full elimination of the stability-detrimental MA+ cation. The best-stability materials will be identified and selected for further study in solar cells to identify the materials exhibiting the best trade-off between efficiency and lifetime. The latter will be then chosen for scaling-up into mini-modules. Double encapsulation will be performed to strongly limit oxygen and water ingress, and the best representative encapsulated mini-modules will undergo standardized aging tests for a thorough stability assessment. These qualification tests will consist in continuous light soaking and damp/heat exposure that are the most critical for the light absorber material.

The three partners will work in close collaboration to carry out this multidisciplinary project. The Institut de Recherche de Chimie-Paris (IRCP, Partner 1) will develop the perovskites chemistry, the films preparation and the characterizations of the layers and devices. The Institut Photovoltaïque d’Île-de-France (IPVF, Partner 2) will do complementary advanced film characterizations, film aging studies and analysis of chemical changes occurring during device aging. The Institut National de l'Énergie Solaire (INES CEA-LITEN, Partner 3) will work on the devices up-scaling, the advanced encapsulation process, and the standardized devices aging tests.

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