Staff directory Haibing Xie



  • 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; 2020. 10.1002/ente.202000134. IF: 3.163

    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: 54.000

    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).

  • 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; 2020. 10.1016/j.ijhydene.2020.03.077. IF: 4.084

    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


  • 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.


  • 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


  • 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

  • Enhanced photoelectrochemical water splitting of hematite multilayer nanowire photoanodes by tuning the surface state via bottom-up interfacial engineering

    Tang P., Xie H., Ros C., Han L., Biset-Peiró M., He Y., Kramer W., Rodríguez A.P., Saucedo E., Galán-Mascarós J.R., Andreu T., Morante J.R., Arbiol J. Energy and Environmental Science; 10 (10): 2124 - 2136. 2017. 10.1039/c7ee01475a. IF: 29.518

    The optimization of multiple interfaces in hematite (α-Fe2O3) based composites for photoelectrochemical water splitting to facilitate charge transport in the bulk is of paramount importance to obtain enhanced solar-to-fuel efficiency. Herein, we report the fabrication of ITO/Fe2O3/Fe2TiO5/FeNiOOH multi-layer nanowires and a series of systematic experiments designed to elucidate the mechanism underlying the interfacial coupling effect of the quaternary hematite composite. The hierarchical ITO/Fe2O3/Fe2TiO5/FeNiOOH nanowires display photocurrents that are more than an order of magnitude greater than those of pristine Fe2O3 nanowires (from 0.205 mA cm-2 to 2.2 mA cm-2 at 1.23 V vs. RHE and 1 Sun), and higher than those of most of the recently reported state-of-the-art hematite composites. Structural, compositional and electrochemical investigations disclose that the surface states (SS) are finely regulated via the atomic addition of an Fe2TiO5 layer and FeNiOOH nanodots, while the upgrading of back contact conductivity and charge donor densities originate from the epitaxial relationship and enhanced Sn doping contributed from the ITO underlayer. We attribute the superior water oxidation performance to the interfacial coupling effect of the ITO underlayer (Sn doping and back contact conductivity promoter), the atomic level Fe2TiO5 coating (Ti doping, surface state density and energy level modulation) and the FeNiOOH nanodot electrocatalyst (regulating surface state energy level). Our work suggests an effective pathway for rational designing of highly active and cost-effective integrated photoanodes for photoelectrochemical water splitting. © The Royal Society of Chemistry.