Marion Provost

Perovskite solar cells (PSCs) are among the most promising photovoltaic technologies, offering high efficiencies and low fabrication costs. However, their widespread deployment is hindered by fundamental challenges limiting performance stability.

L’application de la technologie OLED (diode électroluminescente organique) pour l’affichage est actuellement principalement portée par le marché des écrans de télévision et des smartphones. Les matériaux et les substrats utilisés permettent de produire des dispositifs légers, compacts, voire flexibles, possédant un excellent contraste image et une fréquence de rafraîchissement élevée. Les contraintes technologiques limitant l’industrialisation concernent la durée de vie des dispositifs. D’une part, les matériaux utilisés dans les structures OLEDs sont dégradés en présence d’eau et d’oxygène, il est donc essentiel de passiver le dispositif avec une structure de haute qualité barrière à l’atmosphère. D’autre part, il est nécessaire d’ajouter une protection mécanique en surface, sous forme de capot ou de protection monolithique, modulable en fonction de l’application visée. Ces travaux de thèse visent à développer une nouvelle conception de packaging, intégrant des nanocomposites organiques-inorganiques au sein de l’architecture d’encapsulation multicouche développée au CEA-LETI, et appliquée aux écrans de petite taille (microdisplays) OLED réalisés sur substrat silicium. Ces matériaux permettent de cumuler des propriétés d’ordinaire antagonistes ; celles de la phase organiques (flexible, déposable par voie liquide) et celles de la phase inorganique (barrière au gaz, résistance mécanique et chimique). Les résultats reposent sur le contrôle fin de la morphologie ; le procédé sol-gel a donc été choisi pour sa versatilité. Nous avons montré qu’il était possible de définir plusieurs formulations composites. L’une en particulier, basée sur des nanoparticules de silice intégrées dans une matrice polymère, s’est révélée compatible avec l’encapsulation monolithique des substrats OLED, permettant notamment la reprise de contact électrique. L’ajout de ce matériau au sein de l’architecture de passivation augmente la résistance barrière au gaz et, par extension, la durabilité des dispositifs en conditions climatiques sévères. Utilisé en tant que protection mécanique de surface, cette solution en couche mince n’atteint pas la résistance mécanique des capots de verre, mais permet malgré tout de protéger les substrats pendant toutes les phases de fabrication et de manipulation. L’avantage principal de cette solution packaging réside dans la diminution de l’épaisseur totale, augmentant le contraste en limitant fortement les pertes lumineuses, et ouvrant la porte aux substrats et dispositifs flexibles.

Until recently, bulky ammonium cations, or 2D cations, one of the most promising avenues for interface passivation, have been applied almost exclusively to the p‐type interface of the n‐i‐p architecture. As the perovskite photovoltaics community gradually moves toward the inverse architecture (p‐i‐n), the question of whether to integrate 3D/2D interfaces at the interface between perovskite and the N‐type contact layer is only natural. By comparing different integration strategies, this work highlights the importance of solvent engineering and additive strategies to integrate quasi‐2D perovskite in p‐i‐n devices. It is demonstrated that these strategies enable almost complete conversion of lead iodide (PbI ₂ ) excess through its conversion to quasi‐2D phases, result in a quasi‐Fermi level splitting (QFLS) gain of up to 40 meV, and promote the emergence of quasi‐2D phases of higher dimensions, which are less detrimental to electron extraction. Increasing device efficiency and stability using 2D cations, however, remains a challenge for the p‐i‐n architecture due to the quasi‐2D phases’ intrinsic properties and interfacial mechanical stress at the nanoscale. It is anticipated that, to take full advantage of quasi‐2D perovskites’ superior stability and passivating power, one needs to gain control over the homogeneity, thickness, and phase of the low‐dimensionality layer.

Access to finely tuned thin films that can act as electron transport layer (ETL) and adapt to the absorber composition and whole cell fabrication process is key to achieve efficient perovskite-based solar cells. In this study, the growth of mixed niobium-titanium oxide (Nb-TiO2) thin films by atomic layer deposition and its use to extract photogenerated electrons is reported. Films were obtained at 200 °C from titanium (IV) i-propoxide, (t-butylimido)tris(diethylamido)niobium(V), and water by introducing Nb2O5 growth cycle in a TiO2 matrix. Process parameters (order of precursor introduction, cycle ratio) were optimized; the growth mechanism and the effective Nb incorporation were investigated by an in situ quartz crystal microbalance and x-ray photoelectron spectroscopy. The composition, morphology, structural, and optoelectronic properties of the as-deposited films were determined using a variety of characterization techniques. As a result, a fine control of the film properties (between TiO2 and Nb2O5 ones) could be achieved by tuning Nb content. To allow a successful implementation in solar devices, a comprehensive annealing study under several conditions (temperatures, various atmospheres) was conducted leading to an evolution of the optical properties due to a morphological change. Ultimately, the incorporation of these 15 nm-thick films in mesoscopic perovskite solar cells as ETL shows an improvement of the cell performances and of their stability with increasing Nb content, in comparison of both TiO2 and Nb2O5 pure compounds, reaching power conversion efficiency up to 18.3% and a stability above 80% of its nominal value after 138 h under illumination.

The development of industrially relevant deposition processes for efficient, stable, and inexpensive charge extracting layers is crucial for the commercialization of perovskite solar cells (PSCs). This work demonstrates, for the first time, the deposition of copper thiocyanate (CuSCN) as a low‐cost and reliable hole‐transport layer using slot‐die coating. Methyl ethyl sulfide is thereby used as an asymmetric cosolvent to significantly increase the solubility of CuSCN in the utilized slot‐die ink compared to traditional pure diethyl sulfide‐based solutions. Optimized CuSCN inks allow for the deposition of CuSCN layers on 5 × 10 cm² substrates with a wide range of thicknesses. Multidimensional imaging photoluminescence techniques are used to investigate the uniformity of the CuSCN thin films deposition as well as the influence of the solvent on charge losses. Finally, the CuSCN slot‐die deposition is integrated into a fully upscalable PSC fabrication process showing 19.1% power conversion efficiency for small laboratory cells and 14.7% for 9 cm² minimodules. Furthermore, semitransparent minimodules retain 80% of their initial efficiency after 500 h of constant illumination.

To upscale the emerging perovskite photovoltaic technology to larger-size modules, industrially relevant deposition techniques need to be developed. In this work, the deposition of tin oxide used as an electron extraction layer is established using chemical bath deposition (CBD), a low-cost and solution-based fabrication process. Applying this simple low-temperature deposition method, highly homogeneous SnO₂ films are obtained in a reproducible manner. Moreover, the perovskite layer is prepared by sequentially slot-die coating on top of the n-type contact. The symbiosis of these two industrially relevant deposition techniques allows for the growth of high-quality dense perovskite layers with large grains. The uniformity of the perovskite film is further confirmed by scanning electron microscopy (SEM)/scanning transmission electron microscopy (STEM) analysis coupled with energy dispersive X-ray spectroscopy (EDX) and cathodoluminescence measurements allowing us to probe the elemental composition at the nanoscale. Perovskite solar cells fabricated from CBD SnO₂ and slot-die-coated perovskite show power conversion efficiencies up to 19.2%. Furthermore, mini-modules with an aperture area of 40 cm² demonstrate efficiencies of 17% (18.1% on active area).

This work presents a path to the fabrication of highly efficient, large size 4-Terminal (4T) perovskite silicon tandem. As a first step, our deposition process of perovskite based on spin coating was transferred to slot die coating, enabling large surface areas. Simultaneously, a semitransparent perovskite solar cell was designed to ensure a high optical transmission in the near-infrared (NIR) and we achieved a transmission of 90% at 900 nm, in good agreement with the optical simulation. As a second step, a stack reproducing the perovskite solar cell has been packaged with an n-PERT silicon cell in a box printed in 3D to form a pseudo-tandem with 16 cm ² active area. This device allows to guarantee its durability and to precisely assess the performances of the filtered silicon bottom cell thanks to correct optical alignment. It also minimizes optical losses between both silicon bottom and perovskite top cells. Combining a 16.9% perovskite top cell (active surface of 0.09 cm ² ) deposited by slot die and a 6.4% filtered silicon bottom cell results in an efficiency of 23.3% for a 4T tandem solar cell. Moreover, a filtered silicon solar with 8.2% efficiency is obtained using a perovskite solar cell stack optimized for NIR. The fabrication of 4T tandem over 16 cm ² active area are currently in progress and will be discussed.