Staff directory Sonia Ruiz Raga

Sonia Ruiz Raga

Senior Researcher
La Caixa Incoming 2020
Nanostructured Materials for Photovoltaic Energy



  • Hierarchical carbon nanofibers/carbon nanotubes/NiCo nanocomposites as novel highly effective counter electrode for dye-sensitized solar cells: A structure-electrocatalytic activity relationship study

    Zambrzycki, M; Piech, R; Raga, SR; Lira-Cantu, M; Fraczek-Szczypta, A Carbon; 203: 97 - 110. 2023. 10.1016/j.carbon.2022.11.047.

  • Monitoring the stability and degradation mechanisms of perovskite solar cells by in situ and operando characterization

    Baumann, Fanny; Raga, Sonia R.; Lira-Cantú, Mónica ; 1 (1) 2023. 10.1063/5.0145199.


  • Back-contact perovskite solar cell fabrication via microsphere lithography

    Deng S., Tan B., Chesman A.S.R., Lu J., McMeekin D.P., Ou Q., Scully A.D., Raga S.R., Rietwyk K.J., Weissbach A., Zhao B., Voelcker N.H., Cheng Y.-B., Lin X., Bach U. Nano Energy; 102 (107695) 2022. 10.1016/j.nanoen.2022.107695.

    Back-contact electrodes for hybrid organic-inorganic perovskite solar cells (PSCs) eliminate the parasitic absorption losses caused by the transparent conductive electrodes that are inherent to conventional sandwich-architecture devices. However, the fabrication methods for these unconventional architectures rely heavily on expensive photolithography, which limits scalability. Herein, we present an alternative cost-effective microfabrication technique in which the conventional photolithography process is replaced by microsphere lithography in which a close-packed polystyrene microsphere monolayer acts as the patterning mask for the honeycomb-shaped electrodes. A comprehensive comparison between photolithography and microsphere lithography fabrication techniques was conducted. Using microsphere lithography, we achieve highly efficient devices having a stabilized power conversion efficiency (PCE) of 8.6%, twice the reported value using photolithography. Microsphere lithography also enabled the fabrication of the largest back-contact PSC to date, having an active area of 0.75 cm2 and a stabilized PCE of 2.44%. © 2022 Elsevier Ltd

  • Can Laminated Carbon Challenge Gold? Toward Universal, Scalable, and Low-Cost Carbon Electrodes for Perovskite Solar Cells

    Sepalage G.A., Weerasinghe H., Rai N., Duffy N.W., Raga S.R., Hora Y., Gao M., Vak D., Chesman A.S.R., Bach U., Simonov A.N. Advanced Materials Technologies; 7 (6, 2101148) 2022. 10.1002/admt.202101148. IF: 7.848

    While perovskite solar cell (PSC) efficiencies are soaring at a laboratory scale, these are most commonly achieved with evaporated gold electrodes, which would present a significant expense in large-scale production. This can be remedied through the use of significantly cheaper carbon electrodes that, in contrast to metals, also do not migrate through the device. To this end, the present work investigates simple-to-prepare aluminum-supported carbon electrodes derived from commercially available, inexpensive materials that can be applied onto various hole-transporting materials and enable photovoltaic performances on par with those provided by gold electrodes. Successful integration of the new carbon-based electrode into flexible devices produced by a roll-to-roll printing technology by both pressing and lamination is demonstrated. However, temperature cycling durability tests reveal that the use of carbon electrodes based on commercial pastes is hindered by incompatibility of adhesive additives with the key components of the PSCs under heating. Resolving this issue, tailor-made graphite electrodes devoid of damaging additives are introduced, which improve the PSC stability under temperature cycling test protocol to the level provided by benchmark gold electrodes. The study highlights current challenges in developing laminated carbon electrodes in PSCs and proposes strategies toward the resolution thereof. © 2021 Wiley-VCH GmbH.

  • Ionic Liquid Stabilized Perovskite Solar Modules with Power Conversion Efficiency Exceeding 20%

    Wang Y., Yang Y., Li N., Hu M., Raga S.R., Jiang Y., Wang C., Zhang X.-L., Lira-Cantu M., Huang F., Cheng Y.-B., Lu J. Advanced Functional Materials; 2022. 10.1002/adfm.202204396.

    Metal-halide perovskite solar cells (PSCs) exhibit outstanding power conversion efficiencies (PCEs) when fabricated as mm-sized devices, but creation of high-performing large-area modules that are stable on a sufficiently long timescale still presents a significant challenge. Herein, the quality of large-area perovskite film is improved by using ionic liquid additives via forming a new Pb-N bonding between the ionic liquid and Pb2+. This new bond can be modulated by a critical screening of the anion structure of the ionic liquid. The selected ionic liquid effectively reduces the defects of the perovskite films and markedly elongate their carrier lifetimes. As a result, a champion PCE of 24.4% for small-area (0.148 cm2) devices and 20.4% for larger-area (10.0 cm2) modules under AM 1.5G irradiation is achieved. More importantly, the modified devices retain 90% of their peak PCE after aging for 1900 h at 65 ± 5 °C (ISOS-T-1) and 80% after continuous light soaking for 750 h. The non-encapsulated modules maintained 80% of their peak PCE after 1100 h of aging in the air with a relative humidity of 35 ± 5% and temperature of 25 ± 5 °C under dark (ISOS-D-1), showing great potential for future commercialization. © 2022 Wiley-VCH GmbH.

  • Solution Processable Direct Bandgap Copper-Silver-Bismuth Iodide Photovoltaics: Compositional Control of Dimensionality and Optoelectronic Properties

    Pai N., Chatti M., Fürer S.O., Scully A.D., Raga S.R., Rai N., Tan B., Chesman A.S.R., Xu Z., Rietwyk K.J., Reddy S.S., Hora Y., Sepalage G.A., Glück N., Lira-Cantú M., Bach U., Simonov A.N. Advanced Energy Materials; 12 (32, 2201482) 2022. 10.1002/aenm.202201482.

    The search for lead-free alternatives to lead-halide perovskite photovoltaic materials resulted in the discovery of copper(I)-silver(I)-bismuth(III) halides exhibiting promising properties for optoelectronic applications. The present work demonstrates a solution-based synthesis of uniform CuxAgBiI4+x thin films and scrutinizes the effects of x on the phase composition, dimensionality, optoelectronic properties, and photovoltaic performance. Formation of pure 3D CuAgBiI5 at x = 1, 2D Cu2AgBiI6 at x = 2, and a mix of the two at 1 < x < 2 is demonstrated. Despite lower structural dimensionality, Cu2AgBiI6 has broader optical absorption with a direct bandgap of 1.89 ± 0.05 eV, a valence band level at -5.25 eV, improved carrier lifetime, and higher recombination resistance as compared to CuAgBiI5. These differences are mirrored in the power conversion efficiencies of the CuAgBiI5 and Cu2AgBiI6 solar cells under 1 sun of 1.01 ± 0.06% and 2.39 ± 0.05%, respectively. The latter value is the highest reported for this class of materials owing to the favorable film morphology provided by the hot-casting method. Future performance improvements might emerge from the optimization of the Cu2AgBiI6 layer thickness to match the carrier diffusion length of ≈40–50 nm. Nonencapsulated Cu2AgBiI6 solar cells display storage stability over 240 days. © 2022 The Authors. Advanced Energy Materials published by Wiley-VCH GmbH.


  • Balancing Charge Extraction for Efficient Back-Contact Perovskite Solar Cells by Using an Embedded Mesoscopic Architecture

    Lin X., Lu J., Raga S.R., McMeekin D.P., Ou Q., Scully A.D., Tan B., Chesman A.S.R., Deng S., Zhao B., Cheng Y.-B., Bach U. Advanced Energy Materials; 11 (21, 2100053) 2021. 10.1002/aenm.202100053. IF: 29.368

    As the performance of organic–inorganic halide perovskite solar cells approaches their practical limits, the use of back-contact architectures, which eliminate parasitic light absorption, provides an effective route toward higher device efficiencies. However, a poor understanding of the underlying device physics has limited further performance improvements. Here a mesoporous charge-transporting layer is introduced into quasi-interdigitated back-contact perovskite devices and the charge extraction behavior with an increased interfacial contact area is studied. The results show that the incorporation of a thin mesoporous titanium dioxide layer significantly shortens the charge-transfer lifetime and results in more efficient and balanced charge extraction dynamics. A high short-circuit current density of 21.3 mA cm–2 is achieved using a polycrystalline perovskite layer on a mesoscopic quasi-interdigitated back-contact electrode, a record for this type of device architecture. © 2021 Wiley-VCH GmbH

  • The impact of spiro-OMeTAD photodoping on the reversible light-induced transients of perovskite solar cells

    Tan B., Raga S.R., Rietwyk K.J., Lu J., Fürer S.O., Griffith J.C., Cheng Y.-B., Bach U. Nano Energy; 82 (105658) 2021. 10.1016/j.nanoen.2020.105658. IF: 17.881

    Hole transporting materials (HTMs) play essential roles in facilitating hole extraction and suppressing recombination in lead halide perovskite solar cells (PSCs). High levels of p-doping in HTMs is necessary for achieving high device performance, attributed to an increased electrical conductivity. In this work, we provide evidences that the poor performance of PSCs with low levels of doping (i.e., 4 mol% spiro-OMeTAD+) in spiro-OMeTAD is mainly caused by the presence of a Schottky barrier at the perovskite/spiro-OMeTAD interface, hampering hole injection. Under continuous illumination at open-circuit condition, the barrier gradually diminishes, increasing the PSC power conversion efficiency by 70-fold after 7 h. This process is completely reversible, returning to the initial poor performance after dark storage. We attribute this improvement in performance to a gradual photodoping of spiro-OMeTAD, triggered by the transfer of photogenerated holes and mediated by the slow migration of halide anions from perovskite to compensate the newly formed spiro-OMeTAD+. In-situ parallel analyses with impedance spectroscopy (IS) and photoluminescence are employed to gain insights into the charge dynamics along with light soaking. We find that the Schottky barrier resistance overlays with the recombination signal at the high frequency arc of IS, having important implications for the IS data analysis for PSCs. The work elucidates a major mechanism causing the slow efficiency variations during light/dark cycling, commonly observed in PSCs, which complicates the determination of long-term stability. © 2021 Elsevier Ltd