Publications

2021

1) Enhancing stability of hybrid perovskite solar cells by imidazolium incorporationWeb of Science

Authors:  Tomulescu, Andrei Gabriel;  Leonat, Lucia Nicoleta;  Neatu, Florentina;  Stancu, Viorica;  Toma, Vasilica;  Derbali, Sarah;  Neatu, Stefan;  Rostas, Arpad Mihai;  Besleaga, Cristina;  Patru, Roxana;  Pintilie, Ioana

Published:Aug 2021 in Solar Energy Materials and Solar Cells

DOI: 10.1016/J.SOLMAT.2021.111096

Abstract

Hybrid perovskites based solar cells have demonstrated high conversion efficiency but poor long-term stability. This study reports on the results obtained after doping the CH3NH3PbI2.6Cl0.4 mixed halide perovskite with imidazolium (C3N2H5+, denoted IM) on the “A site” position of a perovskite, to improve photovoltaic performances and stability of hybrid perovskite solar cells. The perovskite films were investigated exhaustively by different characterization techniques: X-ray diffraction, Atomic Force Microscopy, Scanning Electron Microscopy, UV–Vis, X-ray Photoelectron Electron Paramagnetic Resonance spectroscopies, Impedance Spectroscopy and Incident Photon-to-Electron Conversion Efficiency. The photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. The amount of IM inserted in the perovskite play a key role on the film properties. The calculated new tolerance factors according to the “globularity factor” are experimentally proved and thus at doping concentrations greater than 20% for CH3NH3PbI2.6Cl0.4 perovskite the 3D structure is no longer obtained. However, below this value, the IM substituted perovskite film possesses an improved film quality and crystallinity as compared to the pristine film. Substituting MA+ with IM+ provides a favorable way to reduce recombination processes and shows great potential to achieve high stability, and an improved charge generation, resulting in increased PCE values. We find that the optimal percentage of imidazolium incorporation to achieve better stability of solar cells is 6%.

Graphical abstract

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2) Tetragonal-Cubic Phase Transition and Low-Field Dielectric Properties of CH3NH3PbI3 CrystalsWeb of Science

Authors:  Roxana E. Patru;  Hamidreza Khassaf;  Iuliana Pasuk;  Mihaela Botea;  Lucian Trupina;  Constantin-Paul Ganea;  Lucian Pintilie;  Ioana Pintilie

Published:Aug 2021 in Materials

DOI: 10.3390/MA14154215

Abstract

The frequency and temperature dependence of dielectric properties of CH3NH3PbI3 (MAPI) crystals have been studied and analyzed in connection with temperature-dependent structural studies. The obtained results bring arguments for the existence of ferroelectricity and aim to complete the current knowledge on the thermally activated conduction mechanisms, in dark equilibrium and in the presence of a small external a.c. electric field. The study correlates the frequency-dispersive dielectric spectra with the conduction mechanisms and their relaxation processes, as well as with the different transport regimes indicated by the Nyquist plots. The different energy barriers revealed by the impedance spectroscopy highlight the dominant transport mechanisms in different frequency and temperature ranges, being associated with the bulk of the grains, their boundaries, and/or the electrodes’ interfaces.

Graphical abstract

3) Effect of chlorine and bromine on the perovskite crystal growth in mesoscopic heterojunction photovoltaic device

Authors: Hanadi Mehdi, Lucia Nicoleta Leonat, Viorica Stancu, Hamza Saidi, Monica Enculescu, Andrei-Gabriel Tomulescu, Vasilica Toma, Ioana Pintilie, Abdelaziz Bouazizi, Aurelian Catalin Galca,

Published: on-line in february 2022 in Materials Science in Semiconductor Processing

DOI: 10.1016/j.mssp.2022.106558

Abstract:
Organic-inorganic hybrid perovskite solar cells are within the emerging photovoltaic technologies. The combination of different halogen ions, in certain fill fractions, is one of the methods to improve the perovskite film properties. Herein, fabrication and characterization of perovskite cells in standard mesoscopic architecture using one-step deposition method has been done. The role of the halogen ions (Chlorine or Bromine) on crystal structure growth and photoelectric performance has been investigated. X-ray diffraction, scanning electron microscopy, atomic force microscopy and optical microscopy analysis were performed. The microstructure, composition and morphology of CH3NH3PbI1.8Br1.2 and CH3NH3PbI1.8Cl1.2 films are dissimilar, although identical fabrication method was used. Same holds for optical properties, band gap energies of 1.84 eV and 1.63 eV, respectively, being obtained. Integrated in solar cells, the maximum power conversion efficiency of the Br based devices is beyond 10%, while for those based on Cl, the efficiency drops around 5%.

4) Capacitive and Inductive Effects in Perovskite Solar Cells: The Different Roles of Ionic Current and Ionic Charge Accumulation

Authors: Nicolae Filipoiu, Amanda Teodora Preda, Dragos-Victor Anghel , Roxana Patru, Rachel Elizabeth Brophy , Movaffaq Kateb , Cristina Besleaga, Andrei Gabriel Tomulescu, Ioana Pintilie , Andrei Manolescu, and George Alexandru Nemnes

Published: on 28 December 2022 in Phys. Rev. Applied

DOI: 10.1103/PhysRevApplied.18.064087

Abstract: Dynamic hysteresis effects have been long known to occur in the current density-voltage characteristics of perovskite solar cells, with the ionic migration being identified as the primary factor. The hysteretic effects impacted early studies by the uncertainty in the evaluation of the power conversion efficiency, while currently, potential links to degradation mechanisms are the focus. Therefore, understanding ion migration is a central goal, typically addressed by performing a combined large and small signal analysis. The reported large capacitive and inductive effects created controversies with respect to the underlying mechanisms, yielding essentially two classes of models, one based on the large accumulation capacitances and the other based on the ionic modulation of the collected current. We introduce here an equivalent circuit model and interpret these phenomena in terms of recombination current modulation, identifying the distinct contributions from ion current and ionic charge accumulations. These contributions to the recombination current are associated with capacitive and inductive effects, respectively, and we corroborate the numerical simulations with electrochemical impedance spectroscopy measurements. These show the role of the recombination currents of photogenerated carriers in producing both capacitive and inductive effects as the illumination is varied. Moreover, we provide a bridging point between the two classes of models and suggest a framework of investigation of defect states based on the observed inductive behavior, which would further aid the mitigation of the degradation effects.

5) Fundamentals and classification of halide perovskites

Authors: Sarah Derbali, Viorica Stancu,Andrei G. Tomulescu, Cristina Besleaga, George Alexandru Nemnes, Ioana Pintilie and Mihaela Florea

Published: on 29 November 2022, Chapter 2 (pages 19-55) in PEROVSKITES Structure, Synthesis and Applications, Elsevier, Editors: Yiqiang Zhan, Mohammad Khalid, Paola Vivo and Numan Arshid

eBook ISBN: 9780323885232

Paperback ISBN: 9780323885225

DOI: 10.1016/B978-0-323-88522-5.00005-3

6) Ab initio studies on perovskites

Authors: Tudor Luca Mitran, Rachel Elizabeth Brophy, Marina Cuzminschi, Nicolae Filipoiu, Movaffaq Kateb, Ioana Pintilie, Andrei Manolescu and George Alexandru Nemnes

Published: on 29 November 2022, Chapter 5 (pages 153-185) in PEROVSKITES Structure, Synthesis and Applications, Elsevier, Editors: Yiqiang Zhan, Mohammad Khalid, Paola Vivo and Numan Arshid

eBook ISBN: 9780323885232

Paperback ISBN: 9780323885225

DOI: 10.1016/B978-0-323-88522-5.00012-0

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