Staff directory Mónica Lira Cantu

Mónica Lira Cantu

CSIC Research Scientist and Group Leader
Nanostructured Materials for Photovoltaic Energy



  • Additive engineering for stable halide perovskite solar cells

    Pereyra C., Xie H., Lira-Cantu M. Journal of Energy Chemistry; 60: 599 - 634. 2021. 10.1016/j.jechem.2021.01.037. IF: 7.216

    Halide perovskite solar cells (PSCs) have already demonstrated power conversion efficiencies above 25%, which makes them one of the most attractive photovoltaic technologies. However, one of the main bottlenecks towards their commercialization is their long-term stability, which should exceed the 20-year mark. Additive engineering is an effective pathway for the enhancement of device lifetime. Additives applied as organic or inorganic compounds, improve crystal grain growth enhancing power conversion efficiency. The interaction of their functional groups with the halide perovskite (HP) absorber, as well as with the transport layers, results in defect passivation and ion immobilization improving device performance and stability. In this review, we briefly summarize the different types of additives recently applied in PSC to enhance not only efficiency but also long-term stability. We discuss the different mechanism behind additive engineering and the role of the functional groups of these additives for defect passivation. Special emphasis is given to their effect on the stability of PSCs under environmental conditions such as humidity, atmosphere, light irradiation (UV, visible) or heat, taking into account the recently reported ISOS protocols. We also discuss the relation between deep-defect passivation, non-radiative recombination and device efficiency, as well as the possible relation between shallow-defect passivation, ion immobilization and device operational stability. Finally, insights into the challenge and criteria for additive selection are provided for the further stability enhancement of PSCs. © 2021 Science Press

  • Functionalized carbon dots on TiO2 for perovskite photovoltaics and stable photoanodes for water splitting

    Ansón-Casaos A., Hernández-Ferrer J., Vallan L., Xie H., Lira-Cantú M., Benito A.M., Maser W.K. International Journal of Hydrogen Energy; 46 (22): 12180 - 12191. 2021. 10.1016/j.ijhydene.2020.03.077. IF: 4.939

    Various types of fluorescent carbon nanoparticles, often called carbon dots (CDs), are synthesized by different polycondensation methods: microwave irradiation, hydrothermal conditions or solution chemistry at ambient temperature with subsequent chemical functionalization. The CDs are deposited on TiO2 films to be probed as electron transport layers in perovskite photovoltaics and the anode for photoelectrochemical water splitting. Nitrogen CDs, which do not contain oxygen, lead to an increase of around 50 mV in the open circuit voltage of perovskite solar cells. All the CD types produce an improved photocurrent in water splitting, particularly CDs that are functionalized with thiol groups and butyl chains. It is demonstrated that the modified electrode is stable under continuous operation. Other electrochemical characteristics of the electrode, such as the voltammogram shape, onset potentials and open circuit potentials, remain nearly unchanged upon the deposition of CDs. Only the incident photon to current conversion efficiency improves clearly, extending the absorption range by around 20 nm towards longer wavelengths. This study provides new data about mechanisms and electrode arrangements for improving the performance of n-type semiconductors in photovoltaic cells and photoelectrochemical hydrogen production. © 2020 Hydrogen Energy Publications LLC

  • Stress-mediated solution deposition method to stabilize ferroelectric BiFe1-xCrxO3 perovskite thin films with narrow bandgaps

    Jiménez R., Ricote J., Bretos I., Jiménez Riobóo R.J., Mompean F., Ruiz A., Xie H., Lira-Cantú M., Calzada M.L. Journal of the European Ceramic Society; 2021. 10.1016/j.jeurceramsoc.2020.12.042. IF: 4.495

    Ferroelectric oxides with low bandgaps are mainly based on the BiFeO3 perovskite upon the partial substitution of iron with different cations. However, the structural stability of many of these perovskites is only possible by their processing at high pressures (HP, >1GPa) and high temperatures (HT, >700ºC). Preparation methods under these severe conditions are accessible to powders and bulk ceramics. However, transferring these conditions to the fabrication of thin films is a challenge, thus limiting their use in applications. Here, a chemical solution deposition method is devised, which overcomes many of these restrictions. It is based on the application of an external compressive-stress to the film sample during the thermal treatment required for the film crystallization, promoting the formation and stabilization of these HP perovskites. We demonstrate the concept on BiFe1-xCrxO3 (BFCO) thin films deposited on SrTiO3 (STO) substrates and with large chromium contents. The resulting BFCO perovskite films show narrow bandgaps (Eg∼2.57 eV) and an excellent ferroelectric response (remnant polarization, PR∼ 40 μC cm−2). The polarized thin films under illumination present a large out-put power of ∼6.4 μW cm−2, demonstrating their potential for using in self-powered multifunctional devices. This stress-mediated solution deposition method can be extended to other perovskite films which are unviable under conventional deposition methods. © 2021 Elsevier Ltd

  • Unraveling the Key Relationship Between Perovskite Capacitive Memory, Long Timescale Cooperative Relaxation Phenomena, and Anomalous J–V Hysteresis

    Hernández-Balaguera E., del Pozo G., Arredondo B., Romero B., Pereyra C., Xie H., Lira-Cantú M. Solar RRL; 5 (4, 2000707) 2021. 10.1002/solr.202000707. IF: 7.527

    Capacitive response at long time scales seems to remain an elusive feature in the analysis of the electrical properties of perovskite-based solar cells. It belongs to one of the critical anomalous effects that arises from the characteristic phenomenology of this type of emerging photovoltaic devices. Thereby, accurately deducing key capacitance feature of new light harvesting perovskites from electrical measurements represents a significant challenge regarding the interpretation of physical processes and the control of undesired mechanisms, such as slow dynamic effects and/or current density–voltage (J–V) hysteresis. Herein, it is shown that long timescale mechanisms that give rise to hysteresis in stable and high-efficiency quadruple-cation perovskites are not due to a classical capacitive behavior in the sense of ideal charge accumulation processes. Instead, it is a phenomenological consequence of slow memory-based capacitive currents and the underlying cooperative relaxations. A fractional dynamics approach, based on the idea of capacitance distribution in perovskite devices, reliably models the slow transient phenomena and the consequent scan-rate- and bias-dependent hysteresis. Observable for a wide variety of photovoltaic halide perovskites, distributed capacitive effects are rather universal anomalous phenomena, which can be related to the long-time electrical response and hysteresis. © 2021 Wiley-VCH GmbH


  • An Interlaboratory Study on the Stability of All-Printable Hole Transport Material–Free Perovskite Solar Cells

    De Rossi F., Barbé J., Tanenbaum D.M., Cinà L., Castriotta L.A., Stoichkov V., Wei Z., Tsoi W.C., Kettle J., Sadula A., Chircop J., Azzopardi B., Xie H., Di Carlo A., Lira-Cantú M., Katz E.A., Watson T.M., Brunetti F. Energy Technology; 8 (12, 2000134) 2020. 10.1002/ente.202000134. IF: 3.404

    Comparisons between different laboratories on long-term stability analyses of perovskite solar cells (PSCs) is still lacking in the literature. This work presents the results of an interlaboratory study conducted between five laboratories from four countries. Carbon-based PSCs are prepared by screen printing, encapsulated, and sent to different laboratories across Europe to assess their stability by the application of three ISOS aging protocols: (a) in the dark (ISOS-D), (b) under simulated sunlight (ISOS-L), and (c) outdoors (ISOS-O). Over 1000 h stability is reported for devices in the dark, both at room temperature and at 65 °C. Under continuous illumination at open circuit, cells survive only for few hours, although they recover after being stored in the dark. Better stability is observed for cells biased at maximum power point under illumination. Finally, devices operate in outdoors for 30 days, with minor degradation, in two different locations (Barcelona, Spain and Paola, Malta). The findings demonstrate that open-circuit conditions are too severe for stability assessment and that the diurnal variation of the photovoltaic parameters reveals performance to be strongly limited by the fill factor, in the central hours of the day, due to the high series resistance of the carbon electrode. © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Consensus statement for stability assessment and reporting for perovskite photovoltaics based on ISOS procedures

    Khenkin M.V., Katz E.A., Abate A., Bardizza G., Berry J.J., Brabec C., Brunetti F., Bulović V., Burlingame Q., Di Carlo A., Cheacharoen R., Cheng Y.-B., Colsmann A., Cros S., Domanski K., Dusza M., Fell C.J., Forrest S.R., Galagan Y., Di Girolamo D., Grätzel M., Hagfeldt A., von Hauff E., Hoppe H., Kettle J., Köbler H., Leite M.S., Liu S.F., Loo Y.-L., Luther J.M., Ma C.-Q., Madsen M., Manceau M., Matheron M., McGehee M., Meitzner R., Nazeeruddin M.K., Nogueira A.F., Odabaşı Ç., Osherov A., Park N.-G., Reese M.O., De Rossi F., Saliba M., Schubert U.S., Snaith H.J., Stranks S.D., Tress W., Troshin P.A., Turkovic V., Veenstra S., Visoly-Fisher I., Walsh A., Watson T., Xie H., Yıldırım R., Zakeeruddin S.M., Zhu K., Lira-Cantu M. Nature Energy; 5 (1): 35 - 49. 2020. 10.1038/s41560-019-0529-5. IF: 46.495

    Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis. © 2020, The Author(s).

  • Effects of the methylammonium ion substitution by 5-ammoniumvaleric acid in lead trihalide perovskite solar cells: a combined experimental and theoretical investigation

    Urzúa-Leiva R., Narymany Shandy A., Xie H., Lira-Cantú M., Cárdenas-Jirón G. New Journal of Chemistry; 44 (34): 14642 - 14649. 2020. 10.1039/d0nj02748k. IF: 3.288

    In the last decade, lead triiodide perovskite (APbI3) (A: organic cation) solar cells (PSCs) have been broadly studied due to their promising features related to the low cost, easy manufacturing process, and stability. Strategies to improve the device stability include the application of techniques such as compositional engineering of the cation of these halide perovskites, but it is still a complex task to find the right balance between the stability and power conversion efficiency of materials and complete devices. In this work, we performed a combined study of five samples of [5-AVA(1−x)MAx]PbI3(5-AVA: ammonium valeric acid and MA: methylammonium) withx= 1.0, 0.75, 0.5, 0.25 and 0.0, using X-ray diffraction (XRD) and UV-VIS spectroscopy measurements in combination with periodic density functional theory (DFT) based calculations. Our samples showed an optical bandgap of 1.58 eV and the coexistence of the two phases as observed by XRD analyses. The theoretical results of the bandgaps for the no mixed phases (x= 1.0 andx= 0.0) show good agreement with the experiment, obtaining bandgap values overestimated by 0.18 eV and 0.33 eV, respectively. A direct relation between the number of 5-AVA ions in the samples and the stability of the phases was theoretically found and proved through the increment observed in the bandgap and the cohesive energy. We proposed a compositional strategy for perovskites [5-AVA(1−x)MAx]PbI3withxvalues of at most 0.5, based on the small blue-shift and the low absorbance reduction of the spectrum curve, added to the small phase stabilization found. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2020.

  • Multi-component engineering to enable long-term operational stability of perovskite solar cells

    Haibing Xie, Monica Lira-Cantu Journal of Physics Energy; 2 (3, 24008) 2020. 10.1088/2515-7655/ab8278. IF: 0.000

  • Recent advances in fiber-shaped and planar-shaped textile solar cells

    Hatamvand M., Kamrani E., Lira-Cantú M., Madsen M., Patil B.R., Vivo P., Mehmood M.S., Numan A., Ahmed I., Zhan Y. Nano Energy; 71 (104609) 2020. 10.1016/j.nanoen.2020.104609. IF: 16.602

    During the last few years, textile solar cells with planar and fiber-shaped configurations have attracted enormous research interest. These flexible-type solar cells have a huge potential applicability in self-powered and battery-less electronics, which will impact many sectors, and particularly the Internet of Things. Textile solar cells are lightweight, super-flexible, formable, and foldable. Thus, they could be ideal power-harvester alternatives to common flexible solar cells required in smart textiles, electronic textiles, and wearable electronic devices. This review presents a brief overview on fiber-shaped and planar-shaped solar cells, and it introduces the most recent research reports on the different types of textile solar cells, including details on their fabrication techniques. It also addresses the current challenges and limitations of their technology development, and the encountered issues for their future application and integration in novel devices. © 2020 Elsevier Ltd


  • Boosting Photoelectrochemical Water Oxidation of Hematite in Acidic Electrolytes by Surface State Modification

    Tang P.-Y., Han L.-J., Hegner F.S., Paciok P., Biset-Peiró M., Du H.-C., Wei X.-K., Jin L., Xie H.-B., Shi Q., Andreu T., Lira-Cantú M., Heggen M., Dunin-Borkowski R.E., López N., Galán-Mascarós J.R., Morante J.R., Arbiol J. Advanced Energy Materials; 9 (34, 1901836) 2019. 10.1002/aenm.201901836. IF: 24.884

    State-of-the-art water-oxidation catalysts (WOCs) in acidic electrolytes usually contain expensive noble metals such as ruthenium and iridium. However, they too expensive to be implemented broadly in semiconductor photoanodes for photoelectrochemical (PEC) water splitting devices. Here, an Earth-abundant CoFe Prussian blue analogue (CoFe-PBA) is incorporated with core–shell Fe2O3/Fe2TiO5 type II heterojunction nanowires as composite photoanodes for PEC water splitting. Those deliver a high photocurrent of 1.25 mA cm−2 at 1.23 V versus reversible reference electrode in acidic electrolytes (pH = 1). The enhancement arises from the synergic behavior between the successive decoration of the hematite surface with nanolayers of Fe2TiO5 and then, CoFe-PBA. The underlying physical mechanism of performance enhancement through formation of the Fe2O3/Fe2TiO5/CoFe-PBA heterostructure reveals that the surface states’ electronic levels of hematite are modified such that an interfacial charge transfer becomes kinetically favorable. These findings open new pathways for the future design of cheap and efficient hematite-based photoanodes in acidic electrolytes. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Giant bulk photovoltaic effect in solar cell architectures with ultra-wide bandgap Ga2O3 transparent conducting electrodes

    Pérez-Tomás A., Chikoidze E., Dumont Y., Jennings M.R., Russell S.O., Vales-Castro P., Catalan G., Lira-Cantú M., Ton –That C., Teherani F.H., Sandana V.E., Bove P., Rogers D.J. Materials Today Energy; 14 (100350) 2019. 10.1016/j.mtener.2019.100350. IF: 0.000

    The use of ultra-wide bandgap transparent conducting beta gallium oxide (β-Ga2O3) thin films as electrodes in ferroelectric solar cells is reported. In a new material structure for energy applications, we report a solar cell structure (a light absorber sandwiched in between two electrodes - one of them - transparent) which is not constrained by the Shockley–Queisser limit for open-circuit voltage (Voc) under typical indoor light. The solar blindness of the electrode enables a record-breaking bulk photovoltaic effect (BPE) with white light illumination (general use indoor light). This work opens up the perspective of ferroelectric photovoltaics which are not subject to the Shockley-Queisser limit by bringing into scene solar-blind conducting oxides. © 2019 Elsevier Ltd

  • Impact of P3HT materials properties and layer architecture on OPV device stability

    Meitzner R., Faber T., Alam S., Amand A., Roesch R., Büttner M., Herrmann-Westendorf F., Presselt M., Ciammaruchi L., Visoly-Fisher I., Veenstra S., Diaz de Zerio A., Xu X., Wang E., Müller C., Troshin P., Hager M.D., Köhn S., Dusza M., Krassas M., Züfle S., Kymakis E., Katz E.A., Berson S., Granek F., Manceau M., Brunetti F., Polino G., Schubert U.S., Lira-Cantu M., Hoppe H. Solar Energy Materials and Solar Cells; 202 (110151) 2019. 10.1016/j.solmat.2019.110151. IF: 6.019

    We report a cooperative study conducted between different laboratories to investigate organic solar cell degradation with respect to P3HT material properties and different solar cell architectures. Various batches of P3HT were collected from different suppliers reflecting commercial availability as well as properties variability. Among the materials properties explicitly considered were the molar mass, dispersity, regio-regularity, impurities by trace metals and intrinsic doping evaluated from radical concentrations. Each of the participating laboratories contributing test devices applied their own layer stack, i.e. their own device architecture and layout. This variation was appreciated as another parameter for evaluation. Even though a large amount of devices failed due to extrinsic degradation effects, indeed, some materials properties were found to be more important than others for obtaining long lifetimes and high stability of P3HT-based polymer solar cells. © 2019

  • PbZrTiO 3 ferroelectric oxide as an electron extraction material for stable halide perovskite solar cells

    Pérez-Tomas A., Xie H., Wang Z., Kim H.-S., Shirley I., Turren-Cruz S.-H., Morales-Melgares A., Saliba B., Tanenbaum D., Saliba M., Zakeeruddin S.M., Gratzel M., Hagfeldt A., Lira-Cantu M. Sustainable Energy and Fuels; 3 (2): 382 - 389. 2019. 10.1039/c8se00451j. IF: 4.912

    State-of-the-art halide perovskite solar cells employ semiconductor oxides as electron transport materials. Defects in these oxides, such as oxygen vacancies (O vac ), act as recombination centres and, in air and UV light, reduce the stability of the solar cell. Under the same conditions, the PbZrTiO 3 ferroelectric oxide employs O vac for the creation of defect-dipoles responsible for photo-carrier separation and current transport, evading device degradation. We report the application of PbZrTiO 3 as the electron extraction material in triple cation halide perovskite solar cells. The application of a bias voltage (poling) up to 2 V, under UV light, is a critical step to induce charge transport in the ferroelectric oxide. Champion cells result in power conversion efficiencies of ∼11% after poling. Stability analysis, carried out at 1-sun AM 1.5 G, including UV light in air for unencapsulated devices, shows negligible degradation for hours. Our experiments indicate the effect of ferroelectricity, however alternative conducting mechanisms affected by the accumulation of charges or the migration of ions (or the combination of them) cannot be ruled out. Our results demonstrate, for the first time, the application of a ferroelectric oxide as an electron extraction material in efficient and stable PSCs. These findings are also a step forward in the development of next generation ferroelectric oxide-based electronic and optoelectronic devices. © 2019 The Royal Society of Chemistry.

  • Towards Oxide Electronics: a Roadmap

    Coll M., Fontcuberta J., Althammer M., Bibes M., Boschker H., Calleja A., Cheng G., Cuoco M., Dittmann R., Dkhil B., El Baggari I., Fanciulli M., Fina I., Fortunato E., Frontera C., Fujita S., Garcia V., Goennenwein S.T.B., Granqvist C.-G., Grollier J., Gross R., Hagfeldt A., Herranz G., Hono K., Houwman E., Huijben M., Kalaboukhov A., Keeble D.J., Koster G., Kourkoutis L.F., Levy J., Lira-Cantu M., MacManus-Driscoll J.L., Mannhart J., Martins R., Menzel S., Mikolajick T., Napari M., Nguyen M.D., Niklasson G., Paillard C., Panigrahi S., Rijnders G., Sánchez F., Sanchis P., Sanna S., Schlom D.G., Schroeder U., Shen K.M., Siemon A., Spreitzer M., Sukegawa H., Tamayo R., van den Brink J., Pryds N., Granozio F.M. Applied Surface Science; 482: 1 - 93. 2019. 10.1016/j.apsusc.2019.03.312. IF: 5.155

    [No abstract available]


  • A Solar Transistor and Photoferroelectric Memory

    Pérez-Tomás A., Lima A., Billon Q., Shirley I., Catalan G., Lira-Cantú M. Advanced Functional Materials; 28 (17, 1707099) 2018. 10.1002/adfm.201707099. IF: 13.325

    This study presents a new self-powered electronic transistor concept “the solar transistor.” The transistor effect is enabled by the functional integration of a ferroelectric-oxide thin film and an organic bulk heterojunction. The organic heterojunction efficiently harvests photon energy and splits photogenerated excitons into free electron and holes, and the ferroelectric film acts as a switchable electron transport layer with tuneable conduction band offsets that depend on its polarization state. This results in the device photoconductivity modulation. All this (i.e., carrier extraction and poling) is achieved with only two sandwiched electrodes and therefore, with the role of the gating electrode being taken by light. The two-terminal solar-powered phototransistor (or solaristor) thus has the added advantages of a compact photodiode architecture in addition to the nonvolatile functionality of a ferroelectric memory that is written by voltage and nondestructively read by light. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Interfacial Engineering of Metal Oxides for Highly Stable Halide Perovskite Solar Cells

    Mingorance A., Xie H., Kim H.-S., Wang Z., Balsells M., Morales-Melgares A., Domingo N., Kazuteru N., Tress W., Fraxedas J., Vlachopoulos N., Hagfeldt A., Lira-Cantu M. Advanced Materials Interfaces; 5 (22, 1800367) 2018. 10.1002/admi.201800367. IF: 4.834

    Oxides employed in halide perovskite solar cells (PSCs) have already demonstrated to deliver enhanced stability, low cost, and the ease of fabrication required for the commercialization of the technology. The most stable PSCs configuration, the carbon-based hole transport layer-free PSC (HTL-free PSC), has demonstrated a stability of more than one year of continuous operation partially due to the dual presence of insulating oxide scaffolds and conductive oxides. Despite these advances, the stability of PSCs is still a concern and a strong limiting factor for their industrial implementation. The engineering of oxide interfaces functionalized with molecules (like self-assembly monolayers) or polymers results in the passivation of defects (traps), providing numerous advantages such as the elimination of hysteresis and the enhancement of solar cell efficiency. But most important is the beneficial effect of interfacial engineering on the lifetime and stability of PSCs. In this work, the authors provide a brief insight into the recent developments reported on the surface functionalization of oxide interfaces in PSCs with emphasis on the effect of device stability. This paper also discusses the different binding modes, their effect on defect passivation, band alignment or dipole formation, and how these parameters influence device lifetime. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Metal Oxides in Photovoltaics: All-Oxide, Ferroic, and Perovskite Solar Cells

    Pérez-Tomás A., Mingorance A., Tanenbaum D., Lira-Cantú M. The Future of Semiconductor Oxides in Next-Generation Solar Cells; : 267 - 356. 2018. 10.1016/B978-0-12-811165-9.00008-9.

    Semiconductor oxides have been applied in photovoltaic technologies for many years. The remarkable versatility of their properties and the feasibility to be fabricated by simple, low-cost and easily scalable fabrication methods confers oxides a unique place in next generation photovoltaics (NGPVs). Their outstanding ability to preserve or improve device characteristics, even as a noncrystalline (amorphous) material, allows their application in flexible and semitransparent PVs devices and printed electronics. Basic (doped and undoped) semiconductor oxides have demonstrated to provide enhanced lifetime stability to state-of-the-art PVs such as Organic (OPV) and halide perovskite solar cells (PSCs), which is a significant step toward NGPVs industrialization and commercialization. But semiconductor oxides, in their more complex form, can also provide properties like magnetism, ferroelectricity, or pyroelectricity (among others), that collectively with the most classical materials, can deliver novel and innovative features. This chapter documents the most recent results observed when semiconductor oxides are applied in different NGPVs technologies. The chapter covers technologies like all-oxide solar cells where the oxide is not only part of the device but also acts as the main light harvesting material. The chapter also describes the application of oxides as part of OPV and PSCs where semiconductor oxides are mostly applied as barrier layers eliminating the use of expensive and unstable organic semiconductors, enhancing device lifetime. © 2018 Elsevier Inc. All rights reserved.

  • Reconsidering figures of merit for performance and stability of perovskite photovoltaics

    Khenkin M.V., Anoop K.M., Visoly-Fisher I., Galagan Y., Di Giacomo F., Patil B.R., Sherafatipour G., Turkovic V., Rubahn H.-G., Madsen M., Merckx T., Uytterhoeven G., Bastos J.P.A., Aernouts T., Brunetti F., Lira-Cantu M., Katz E.A. Energy and Environmental Science; 11 (4): 739 - 743. 2018. 10.1039/c7ee02956j. IF: 30.067

    The development of hybrid organic-inorganic halide perovskite solar cells (PSCs) that combine high performance and operational stability is vital for implementing this technology. Recently, reversible improvement and degradation of PSC efficiency have been reported under illumination-darkness cycling. Quantifying the performance and stability of cells exhibiting significant diurnal performance variations is challenging. We report the outdoor stability measurements of two types of devices showing either reversible photo-degradation or reversible efficiency improvement under sunlight. Instead of the initial (or stabilized) efficiency and T80 as the figures of merit for the performance and stability of such devices, we propose using the value of the energy output generated during the first day of exposure and the time needed to reach its 20% drop, respectively. The latter accounts for both the long-term irreversible degradation and the reversible diurnal efficiency variation and does not depend on the type of process prevailing in a given perovskite cell. © 2018 The Royal Society of Chemistry.


  • Effect of cs-incorporated NiOx on the performance of perovskite solar cells

    Kim H.-S., Seo J.-Y., Xie H., Lira-Cantu M., Zakeeruddin S.M., Gratzel M., Hagfeldt A. ACS Omega; 2 (12): 9074 - 9079. 2017. 10.1021/acsomega.7b01179.

    The effect of Cs-incorporated NiOx on perovskite solar cells with an inverted structure was investigated, where NiOx and PCBM were used as selective contacts for holes and electrons, respectively. It was found that the generation of an Ni phase in an NiOx layer was significantly suppressed by employing cesium. Furthermore, Cs-incorporated NiOx enabled holes to be efficiently separated at the interface, showing the improved photoluminescent quenching and thus generating higher short-circuit current. The effect of Cs incorporation was also prominent in the inhibition of recombination. The recombination resistance of Cs-incorporated NiOx was noticeably increased by more than three-fold near the maximum power point leading to a higher fill factor of 0.78 and consequently a higher power conversion efficiency of 17.2% for the device employing Cs-incorporated NiOx. © 2017 American Chemical Society

  • Incorporation of Counter Ions in Organic Molecules: New Strategy in Developing Dopant-Free Hole Transport Materials for Efficient Mixed-Ion Perovskite Solar Cells

    Zhang J., Xu B., Yang L., Mingorance A., Ruan C., Hua Y., Wang L., Vlachopoulos N., Lira-Cantú M., Boschloo G., Hagfeldt A., Sun L., Johansson E.M.J. Advanced Energy Materials; 7 (14) 2017. 10.1002/aenm.201602736. IF: 16.721

    Hole transport matertial (HTM) as charge selective layer in perovskite solar cells (PSCs) plays an important role in achieving high power conversion efficiency (PCE). It is known that the dopants and additives are necessary in the HTM in order to improve the hole conductivity of the HTM as well as to obtain high efficiency in PSCs, but the additives can potentially induce device instability and poor device reproducibility. In this work a new strategy to design dopant-free HTMs has been presented by modifying the HTM to include charged moieties which are accompanied with counter ions. The device based on this ionic HTM X44 dos not need any additional doping and the device shows an impressive PCE of 16.2%. Detailed characterization suggests that the incorporated counter ions in X44 can significantly affect the hole conductivity and the homogeneity of the formed HTM thin film. The superior photovoltaic performance for X44 is attributed to both efficient hole transport and effective interfacial hole transfer in the solar cell device. This work provides important insights as regards the future design of new and efficient dopant free HTMs for photovotaics or other optoelectronic applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Perovskite solar cells: Stability lies at interfaces

    Lira-Cantú M. Nature Energy; 2 (7, 17115) 2017. 10.1038/nenergy.2017.115. IF: 9.086

    [No abstract available]

  • The Future of Semiconductor Oxides in Next-Generation Solar Cells

    Lira-Cantú M. The Future of Semiconductor Oxides in Next-Generation Solar Cells; : 1 - 543. 2017. .

    The Future of Semiconductor Oxides in Next-Generation Solar Cells begins with several chapters covering the synthesis of semiconductor oxides for NGSCs. Part II goes on to cover the types and applications of NGSCs currently under development, while Part III brings the two together, covering specific processing techniques for NGSC construction. Finally, Part IV discusses the stability of SO solar cells compared to organic solar cells, and the possibilities offered by hybrid technologies. This comprehensive book is an essential reference for all those academics and professionals who require thorough knowledge of recent and future developments in the role of semiconductor oxides in next generation solar cells. © 2018 Elsevier Inc. All rights reserved.


  • Above-Bandgap Photovoltages in Antiferroelectrics

    Pérez-Tomás A., Lira-Cantú M., Catalan G. Advanced Materials; 28 (43): 9644 - 9647. 2016. 10.1002/adma.201603176. IF: 18.960

    The closed circuit photocurrent and open circuit photovoltage of antiferroelectric thin films were characterized both in their ground (antipolar) state and in their polarized state. A sharp transition happens from near zero to large photovoltages as the polarization is switched on, consistent with the activation of the bulk photovoltaic effect. The AFE layers have been grown by a solution processing method (sol?gel synthesis followed by spin coating deposition) onto fluorine-doped tin oxide (FTO), a transparent conducting oxide with low sheet resistance and a higher resilience to high-temperature processing than indium tin oxide and a standard for solar cells such as organometal trihalide perovskites. Light absorption confirmed that the PZO films are, as expected, wide-band gap semiconductors with a gap of 3.7.8 eV and thus highly absorbing in the near-ultraviolet range. On a virgin sample, there is no shortcircuit photocurrent, consistent with the antipolar nature of the ground state. As an external bias voltage is applied, the current remains negligible until suddenly, at the coercive voltage, a spike is observed, corresponding to the transient displacement current caused by the onset of polarization.

  • Comparative indoor and outdoor degradation of organic photovoltaic cells via inter-laboratory collaboration

    Owens C., Ferguson G.M., Hermenau M., Voroshazi E., Galagan Y., Zimmermann B., Rösch R., Angmo D., Teran-Escobar G., Uhrich C., Andriessen R., Hoppe H., Würfel U., Lira-Cantu M., Krebs F.C., Tanenbaum D.M. Polymers; 8 (1, 1) 2016. 10.3390/polym8010001. IF: 2.944

    We report on the degradation of organic photovoltaic (OPV) cells in both indoor and outdoor environments. Eight different research groups contributed state of the art OPV cells to be studied at Pomona College. Power conversion efficiency and fill factor were determined from IV curves collected at regular intervals over six to eight months. Similarly prepared devices were measured indoors, outdoors, and after dark storage. Device architectures are compared. Cells kept indoors performed better than outdoors due to the lack of temperature and humidity extremes. Encapsulated cells performed better due to the minimal oxidation. Some devices showed steady aging but many failed catastrophically due to corrosion of electrodes not active device layers. Degradation of cells kept in dark storage was minimal over periods up to one year. © 2015 by the authors.

  • EU COST Action MP1307 - Unravelling the degradation mechanisms of emerging solar cell technologies

    Aernouts T., Brunetti F., De La Fuente J., Espinosa N., Urbina A., Fonrodona M., Lira-Cantu M., Galagan Y., Hoppe H., Katz E., Ramos M., Riede M., Vandewal K., Veenstra S., Von Hauff E. Proceedings of the 18th Mediterranean Electrotechnical Conference: Intelligent and Efficient Technolo; ( 7495310) 2016. 10.1109/MELCON.2016.7495310.

    Organic and hybrid perovskite based solar cells have a huge potential to significantly contribute to a clean electricity supply of the future. However, so far they exhibit complex and hierarchical degradation paths and their understanding can only be acquired through the application of complementary chemical and physical characterization techniques. This limited device stability is the main hurdle for a successful and large scale market introduction of these emerging solar cell technologies. Our StableNextSol Action has created a highly interdisciplinary network of laboratories, as well as corresponding industry, overall more than 120 partners, with complementary analytical techniques for the study and understanding of the degradation mechanisms occurring in state-of-the-art devices. Our Action integrates and generates fundamental knowledge and expertise to foster disruptive innovations targeted to mitigate device failure and to propose and develop new concepts for more stable solar cells. Value is added to the entire value chain of photovoltaic research at European and international level, as well as variety decision makers in the public sector by supporting specialisation policy and standards still lacking in this research field. The outcome of the Action will contribute to resolve the global challenges facing the industry and this COST Action initiative has brought together all these expertises and resources to promote the cooperation between different sectors, academia, public authorities and industry. © 2016 IEEE.

  • Flexible ITO-free organic solar cells applying aqueous solution-processed V2O5 hole transport layer: An outdoor stability study

    Lima F.A.S., Beliatis M.J., Roth B., Andersen T.R., Bortoti A., Reyna Y., Castro E., Vasconcelos I.F., Gevorgyan S.A., Krebs F.C., Lira-Cantu M. APL Materials; 4 (2, 026104) 2016. 10.1063/1.4942638. IF: 4.323

    Solution processable semiconductor oxides have opened a new paradigm for the enhancement of the lifetime of thin film solar cells. Their fabrication by low-cost and environmentally friendly solution-processable methods makes them ideal barrier (hole and electron) transport layers. In this work, we fabricate flexible ITO-free organic solar cells (OPV) by printing methods applying an aqueous solution-processed V2O5 as the hole transport layer (HTL) and compared them to devices applying PEDOT:PSS. The transparent conducting electrode was PET/Ag/PEDOT/ZnO, and the OPV configuration was PET/Ag/PEDOT/ZnO/P3HT:PC60BM/HTL/Ag. Outdoor stability analyses carried out for more than 900 h revealed higher stability for devices fabricated with the aqueous solution-processed V2O5. © 2016 Author(s).

  • Performance and stability of mixed FAPbI3(0.85)MAPbBr3(0.15) halide perovskite solar cells under outdoor conditions and the effect of low light irradiation

    Reyna Y., Salado M., Kazim S., Pérez-Tomas A., Ahmad S., Lira-Cantu M. Nano Energy; 30: 570 - 579. 2016. 10.1016/j.nanoen.2016.10.053. IF: 11.553

    We demonstrate for the first time, the real lifetime response of mixed halide perovskite solar cells (PSCs) for >1000 h under outdoor conditions and the exceptional photoresponse observed at low-light intensities attributed to the ionic-electronic nature of the material. The investigated devices were fabricated by utilizing mixed perovskites containing formamidinium (FA) and methylammonium (MA) cations, in a one step solution-process method through a solvent engineering approach. The devices’ architecture is FTO/TiO2 (blocking layer) TiO2 (mesoporous)/FAPbI3(0.85)MAPbBr3(0.15)/Spiro-OMeTAD/Au. Notably, low short circuit current (Jsc) was observed at low light intensities (<50 W/m2) together with high open circuit potential build-up, which resulted in high PCEs. This response is in agreement with a “double electronic-ionic transport” model of the halide perovskite where the ionic component dominates at low light intensities and the electronic component dictates at high light irradiances. Our results highlight the exceptional stability of mixed MA/FA mesoscopic PSCs when operated for >1000 h under real outdoor conditions and the strong ionic component observed at low light irradiation. © 2016 Elsevier Ltd


  • Comparative indoor and outdoor degradation of organic photovoltaic cells via inter-laboratory collaboration

    Owens C., Ferguson G.M., Hermenau M., Voroshazi E., Galagan Y., Zimmermann B., Rosch R., Angamo D., Teran G., Uhrich C., Andriessen R., Hoppe H., Wurfel U., Lira-Cantu M., Krebs F., Tanenbaum D. 2015 IEEE 42nd Photovoltaic Specialist Conference, PVSC 2015; (7356178) 2015. 10.1109/PVSC.2015.7356178.

    We report on the degradation of organic photovoltaic (OPV) cells in both indoor and outdoor environments. Eight different research groups contributed state of the art OPV cells to be studied at Pomona College. Power conversion efficiency, fill factor, and IV curves were collected at regular intervals over six to eight months. Similarly prepared devices were measured indoors, outdoors, and after dark storage. Device architectures are compared. Cells kept indoors performed better than outdoors due to the lack of temperature and humidity extremes. Encapsulated cells performed better due to the minimal oxidation. Some devices showed steady aging but many failed catastrophically due to corrosion of electrodes not active device layers. Degradation of cells kept in dark storage was minimal over periods up to one year. © 2015 IEEE.

  • Electrochemically synthesized mesoporous thin films of ZnO for highly efficient dye sensitized solar cells

    Lima F.A.S., Vasconcelos I.F., Lira-Cantu M. Ceramics International; 41 (8, 10350): 9314 - 9320. 2015. 10.1016/j.ceramint.2015.03.271. IF: 2.605

    Abstract In this work, nanostructured thin films of ZnO were electrochemically grown on FTO substrates. The morphology was tuned by modifying the synthesis parameters. The synthesis was carried out by applying Zn(NO3)·6H2O as the sole component of the aqueous electrolyte, avoiding the use of capping agents. The composition and morphology of the prepared ZnO were characterized by energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM), respectively. The as-deposited films were applied as electrodes in dye sensitized solar cells (DSCs). The performance of the cells was investigated by J×V curves and IPCE (incident photon to charge carrier efficiency) measurements. The SEM analysis demonstrated a direct relationship between ZnO morphology and Zn precursor concentration. It has been shown that the lower the concentration is, the more porous the morphology is. Increasing the amount of dye adsorbed on the ZnO decreased the power conversion efficiency of the final DSCs. The best cell presented the following parameters: open circuit voltage VOC=0.59V, short circuit current JSC=7.64mA/cm2, fill factor FF=50.41%, and power conversion efficiency PCE=2.27%. © 2015 Elsevier Ltd and Techna Group S.r.l.

  • Emerging thin-film photovoltaics: Stabilize or Perish

    Von Hauff E., Lira-Cantu M., Brown T.M., Hoppe H. Advanced Energy Materials; 5 (20, 1501924) 2015. 10.1002/aenm.201501924. IF: 16.146

    [No abstract available]

  • Enhanced photovoltaic performance of inverted hybrid bulk-heterojunction solar cells using TiO2/reduced graphene oxide films as electron transport layers

    Morais A., Alves J.P.C., Lima F.A.S., Lira-Cantu M., Nogueira A.F. Journal of Photonics for Energy; 5 (1, 57408) 2015. 10.1117/1.JPE.5.057408. IF: 1.366

    In this study, we investigated inverted hybrid bulk-heterojunction solar cells with the following configuration: fluorine-doped tin oxide (FTO) jTiO2/RGOjP3HT:PC61BMjV2O5 or PEDOT:PSS|Ag. The TiO2/GO dispersions were prepared by sol-gel method, employing titanium isopropoxide and graphene oxide (GO) as starting materials. The GO concentration was varied from 0.1 to 4.0 wt%. The corresponding dispersions were spin-coated onto FTO substrates and a thermal treatment was performed to remove organic materials and to reduce GO to reduced graphene oxide (RGO). The TiO2/RGO films were characterized by X-ray diffraction, Raman spectroscopy, and microscopy techniques. Atomic force microscopy (AFM) images showed that the addition of RGO significantly changes the morphology of the TiO2 films, with loss of uniformity and increase in surface roughness. Independent of the use of V2O5 or PEDOT: PSS films as the hole transport layer, the incorporation of 2.0 wt% of RGO into TiO2 films was the optimal concentration for the best organic photovoltaic performance. The solar cells based on TiO2/RGO (2.0 wt%) electrode exhibited a ~22.3% and ~28.9% short circuit current density (Jsc) and a power conversion efficiency enhancement, respectively, if compared with the devices based on pure TiO2 films. Kelvin probe force microscopy images suggest that the incorporation of RGO into TiO2 films can promote the appearance of regions with different charge dissipation capacities. © 2015 Society of Photo-Optical Instrumentation Engineers.

  • Procedures and practices for evaluating thin-film solar cell stability

    Roesch R., Faber T., Von Hauff E., Brown T.M., Lira-Cantu M., Hoppe H. Advanced Energy Materials; 5 (20, 1501407) 2015. 10.1002/aenm.201501407. IF: 16.146

    During the last few decades, and in some cases only the last few years, novel thin-film photovoltaic (PV) technologies such as dye-sensitized solar cells (DSSC), organic solar cells (OPV), and, more recently, perovskite-based solar cells (PSC) have been growing in maturity with respect to device performance and device stability. Together with new material systems, novel device architectures have also been introduced. Both parameters will have an effect on the overall device stability. In order to improve the understanding of degradation effects and how they can be prevented, stress testing under different conditions is commonly applied. By careful combination of stress factors and thorough analysis of photovoltaic parameter decaying curves, an understanding of the underlying degradation pathways can be gained. With the help of standardized and accelerated stress tests, as described in the ISOS-protocols, statements concerning application lifetimes can finally be made and compared among different labs. Once a photovoltaic technology has proven long lasting durability, the ultimate barrier for entering the commercial market are the IEC tests, taking a deeper look on overall safety and reliability, not only on durability. Here, the most prominent stress tests are reviewed, discussed and extended with respect to learning the most about photovoltaic device stability. Common procedures and practices for evaluating thin-film solar cell stability and durability are reviewed with respect to their applicability for predicting failure routes and application lifetimes. Suggestions for the reporting of detailed stress factors, photovoltaic parameters with sufficient statistical weight, and new figures of merit are made with the goal of steepening the learning curve towards real applications. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • Vertically Aligned ZnO/Inx S y Core-Shell Nanorods for High Efficient Dye-Sensitized Solar Cells

    Gonzalez-Valls I., Ballesteros B., Lira-Cantu M. Nano; 10 (7, 1550103) 2015. 10.1142/S1793292015501039. IF: 1.090

    Innovative vertically aligned ZnO/InxSy nanorod (NR) electrodes were prepared by successive ion layer adsorption and reaction (SILAR) technique. The InxSy shell layer was deposited on top of ZnO NR electrodes of two different lengths, ~1.6 μm and ~3.2 μm. Two sulfur contents on the InxSy shell layer with different layer thicknesses were analyzed. These electrodes were fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), Energy-dispersive x-ray spectroscopy (EDS), Infrared spectroscopy (FT-IR), x-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) and then applied in dye-sensitized solar cells (DSC). Power conversion efficiency of 2.32% was observed when a low-sulfur content InxSy shell layer was applied in comparison to the stoichiometric In2S3 shell layer (0.21%) or the bare ZnO NRs (0.87%). In the case of low sulfur content, a shell layer of In(OH)xSy or/and In(OH)3 is formed as observed by the presence of-OH observed by FTIR analyses. The presence of higher amounts of hydroxide groups modifies the bandgap and work function of the InxSy shell and facilitates dye adsorption, increasing the final solar cell performance. © 2015 World Scientific Publishing Company. © 2015 World Scientific Publishing Company.


  • A round robin study of flexible large-area roll-to-roll processed polymer solar cell modules

    Monica Lira-Cantu; ichael Gratzel; Panagiotis Lianos; Eugene A. Katz; Wolfgang Lohwasser; Bertrand Jannon et al. Solar Energy Materials and Solar Cells; 2009. .


  • Hybrid materials based on Vanadyl Phosphate and Conducting Polymers as Cathodes in Rechargeable Lithium Cells.

    A. Karina Cuentas-Gallegos; R. Vijayaraghavan; Mónica Lira-Cantú; Nieves Casañ-Pastor; Pedro Gómez-Romero Boletin de la Sociedad Espanola de Ceramica y Vidrio; 43 (2): 429 - 433. 2004. .