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Erika Colin-Ulloa

Bio: Erika Colin-Ulloa is an academic researcher. The author has contributed to research in topics: Materials science & Spectroscopy. The author has an hindex of 3, co-authored 10 publications receiving 16 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article , a planar perovskite solar cell (PSC) is fabricated with additions of 5 wt% of polyethylene oxide (PEO) and the highest PCE of 18.03% was obtained.
Abstract: In this paper, we use Polyethylene Oxide (PEO) particles to control the morphology of Formamidinium (FA)-rich perovskite films and achieve large grains with improved optoelectronic properties. Consequently, a planar perovskite solar cell (PSC) is fabricated with additions of 5 wt% of PEO, and the highest PCE of 18.03% was obtained. This solar cell is also shown to retain up to 80% of its initial PCE after about 140 h of storage under the ambient conditions (average relative humidity of 62.5 ± 3.25%) in an unencapsulated state. Furthermore, the steady-state PCE of the PEO-modified PSC device remained stable for long (over 2500 s) under continuous illumination. This addition of PEO particles is shown to enable the tuning of the optoelectronic properties of perovskite films, improvements in the overall photophysical properties of PSCs, and an increase in resistance to the degradation of PSCs.

4 citations

Journal ArticleDOI
TL;DR: In this paper , the nature of photoexcitations and their dynamics in three different members of the MXene family, Ti3C2, Mo2Ti2C3, and Nb2C, were investigated using two complementary pump-probe techniques, transient optical absorption, and time-resolved terahertz (THz) spectroscopy.
Abstract: 2D MXenes have diverse and chemically tunable optical properties that arise from an interplay between free carriers, interband transitions, and plasmon resonances. The nature of photoexcitations and their dynamics in three different members of the MXene family, Ti3C2, Mo2Ti2C3, and Nb2C, are investigated using two complementary pump‐probe techniques, transient optical absorption, and time‐resolved terahertz (THz) spectroscopy. Measurements reveal pronounced plasmonic effects in the visible and near‐IR in all three. Optical excitation, with either 400 or 800 nm pulses, results in a rapid increase in lattice temperature, evidenced by a pronounced broadening of the plasmon mode that presents as a plasmon bleach in transient absorption measurements. Observed kinetics of plasmon bleach recovery provide a means to monitor lattice cooling. Remarkably slow cooling, proceeding over hundreds of picoseconds to nanoseconds time scales, implies MXenes have low thermal conductivities. The slowest recovery kinetics are observed in the MXene with the highest free carrier density, viz. Ti3C2, that supports phonon scattering by free carriers as a possible mechanism limiting thermal conductivity. These new insights into photoexcitation dynamics can facilitate their applications in photothermal solar energy conversion, plasmonic devices, and even photothermal therapy and drug delivery.

4 citations

Journal ArticleDOI
TL;DR: In this paper , a scalable, one-pot synthesis of one-dimensional, titania lepidocrocite microfilaments was demonstrated by reacting Ti-containing water-insoluble, earth abundant compounds such as TiC, TiB2, TiN, etc., with tetraalkylammonium hydroxide, TMAOH, for a few days at 85 °C under ambient pressure.
Abstract: We recently demonstrated scalable, one-pot syntheses of one-dimensional, titania lepidocrocite microfilaments by reacting Ti-containing water-insoluble, earth-abundant compounds such as TiC, TiB2, TiN, etc., with tetraalkylammonium hydroxide, TMAOH, for a few days at 85 °C under ambient pressure. The resulting one-dimensional lepidocrocite (1DL) titania-based nanofilaments, NFs, tend to self-align along the [100] growth direction to form microfilaments that sometimes self-align into pseudo-two-dimensional (2D) sheets. With sub-square-nanometer cross sections, the resulting band gap energy, Eg, at 4.0 eV is one of the highest ever reported for a titania material. Despite a large band gap, the nanofilaments exhibit significant absorbance throughout the visible spectrum ascribable to intra-gap defect states based on UV–Vis absorbance data and ultraviolet photoelectron spectroscopy (UPS). UP spectra demonstrate work functions of 4.0 ± 0.3 eV vs vacuum and Fermi energies of 3.8 ± 0.1 eV with respect to the valence band edge. Transient absorption (TA) spectroscopy of the 1DL nanofilament thin films with sub-band-gap, visible-light illumination reveals photoexcitations with lifetimes in excess of nanoseconds. In combination with the established oxidative stability, long-lived visible photoexcitations bring forward possible applications of 1DL nanofilaments in photocatalysis and optoelectronics.

2 citations

Proceedings ArticleDOI
15 Mar 2023
TL;DR: In this paper , a comprehensive study of the optical properties of three members of the MXene family, Ti3C, T 2.T , Mo .
Abstract: MXenes are a new class of intrinsically metallic 2D materials. Their wide range of optoelectronic properties they demonstrate as a function of their chemical composition suggest applications in electronic and photonic devices. In this work we present a comprehensive study of the optical properties of three members of the MXene family, Ti3C2Tz, Mo2Ti2C3Tz, and Nb2CTz, using ultrafast transient optical absorption and THz spectroscopy. We find that those properties result from a complicated interaction between free carriers, interband transitions and localized surface plasmon resonances. Elucidating the nature of photoexcitation and dynamics of carriers in these emergent materials will lay the foundation for their potential for optoelectronic applications.

Cited by
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Journal ArticleDOI
TL;DR: In this paper , the dispersion stability and thermophysical characteristics of water-based alumina (Al2O3), graphene oxide (GO) and their hybrid nanofluids (HNF) at different mixing ratios were investigated.

8 citations

Journal ArticleDOI
TL;DR: In this paper , an AASC using Mo1.33CTz MXene films as negative electrode and tetramethylammonium cation intercalated birnessite (TMA+-MnO2) films as the positive electrode in a 21 mol kg−1 lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) electrolyte was reported.
Abstract: Aqueous asymmetric supercapacitors (AASCs) can have high voltages and high energy densities. However, the rational design of AASCs with proper negative and positive electrodes remains a challenge. Herein, we report on an AASC using Mo1.33CTz MXene films as the negative electrode, and tetramethylammonium cation intercalated birnessite (TMA+-MnO2) films as the positive electrode in a 21 mol kg−1 lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) electrolyte. Benefiting from a high, stable voltage of 2.5 V, an energy density of 86.5 Wh L−1 at 2 mV s−1 and a power density of 10.3 kW L−1 at 1 V s−1 were achieved. The cells also exhibit excellent cycling stability (>98 % after 1,0000 cycles at 100 mV s−1) and a 51.1 % voltage retention after 10 h. This good performance is attributed to the high stable potential window and high volumetric capacitances of both Mo1.33CTz and TMA+-MnO2 electrodes in highly concentrated electrolytes. This work provides a roadmap for developing high performance AASCs with high voltages and high energy/power densities, with relatively slow self-discharge rates.

5 citations

Journal ArticleDOI
TL;DR: In this article , an effective additive molecule is designed with heterovalent substitution and antioxidant functions, whereby an organic metal coordination compound of tris(2,4−pentanedionato)gallium (TPGa) is employed to upgrade the quality of perovskite films.
Abstract: All‐perovskite tandem solar cells are promising for breaking through the single‐junction Shockley–Queisser limit, and that potentially raises interest in configuring efficient Sn‐Pb alloyed narrow‐bandgap perovskite solar cells (PSCs). However, the Sn‐Pb alloyed perovskites are commonly plagued by uncontrollable crystallization dynamics and severe p‐doping levels. Herein, an effective additive molecule is designed with heterovalent substitution and antioxidant functions, whereby an organic metal coordination compound of tris(2,4‐pentanedionato)gallium (TPGa) is employed to upgrade the quality of perovskite films. Ga3+ substitution obviously boosts the formation energy of Sn vacancies and heals the trap states. Meanwhile, the crystal structure evolution process is improved by the anchoring effect of 2,4‐pentanedionato. The PSCs incorporating these improvements deliver not only a power conversion efficiency of 21.5% but also outstanding stability, as demonstrated by retaining 80% of the initial efficiency for over 1500 h. In addition, 23.14%‐efficient all‐perovskite tandem solar cells are further obtained by pairing this PSC with a wide‐bandgap (1.74 eV) top cell. This study supports the feasibility of doping trivalent ions into the Sn‐Pb alloyed perovskites to compromise the self‐p‐doping effect and highlights the importance of acetylacetone for passivating defects and hindering oxidation.

3 citations

Journal ArticleDOI
TL;DR: In this paper , a scalable, one-pot synthesis of one-dimensional, titania lepidocrocite microfilaments was demonstrated by reacting Ti-containing water-insoluble, earth abundant compounds such as TiC, TiB2, TiN, etc., with tetraalkylammonium hydroxide, TMAOH, for a few days at 85 °C under ambient pressure.
Abstract: We recently demonstrated scalable, one-pot syntheses of one-dimensional, titania lepidocrocite microfilaments by reacting Ti-containing water-insoluble, earth-abundant compounds such as TiC, TiB2, TiN, etc., with tetraalkylammonium hydroxide, TMAOH, for a few days at 85 °C under ambient pressure. The resulting one-dimensional lepidocrocite (1DL) titania-based nanofilaments, NFs, tend to self-align along the [100] growth direction to form microfilaments that sometimes self-align into pseudo-two-dimensional (2D) sheets. With sub-square-nanometer cross sections, the resulting band gap energy, Eg, at 4.0 eV is one of the highest ever reported for a titania material. Despite a large band gap, the nanofilaments exhibit significant absorbance throughout the visible spectrum ascribable to intra-gap defect states based on UV–Vis absorbance data and ultraviolet photoelectron spectroscopy (UPS). UP spectra demonstrate work functions of 4.0 ± 0.3 eV vs vacuum and Fermi energies of 3.8 ± 0.1 eV with respect to the valence band edge. Transient absorption (TA) spectroscopy of the 1DL nanofilament thin films with sub-band-gap, visible-light illumination reveals photoexcitations with lifetimes in excess of nanoseconds. In combination with the established oxidative stability, long-lived visible photoexcitations bring forward possible applications of 1DL nanofilaments in photocatalysis and optoelectronics.

2 citations

Journal ArticleDOI
TL;DR: In this article , a halogen-free Ti3 C2 Tx was synthesized using NaOH-based etching solution, which exhibits a lower water contact angle (34.5°) and work function (3.6 eV).
Abstract: Surface chemistry influences not only physicochemical properties but also safety and applications of MXene nanomaterials. Fluorinated Ti3 C2 Tx MXene, synthesized using conventional HF-based etchants, raises concerns regarding harmful effects on electronics and toxicity to living organisms. In this study, well-delaminated halogen-free Ti3 C2 Tx flakes are synthesized using NaOH-based etching solution. The transversal surface plasmon mode of halogen-free Ti3 C2 Tx MXene (833 nm) confirmed red-shift compared to conventional Ti3 C2 Tx (752 nm), and the halogen-free Ti3 C2 Tx MXene has a different density of state by the high proportion of -O and -OH terminations. The synthesized halogen-free Ti3 C2 Tx exhibits a lower water contact angle (34.5°) and work function (3.6 eV) than those of fluorinated Ti3 C2 Tx (49.8° and 4.14 eV, respectively). The synthesized halogen-free Ti3 C2 Tx exhibits high biocompatibility with the living cells, as evidenced by no noticeable cytotoxicity, even at very high concentrations (2000 µg mL⁻1 ), at which fluorinated Ti3 C2 Tx caused ≈50% reduction in cell viability upon its oxidation. Additionally, the oxidation stability of halogen-free Ti3 C2 Tx is enhanced unexpectedly, which cumulatively provides a good rationale for pursuing the halogen-free routes for synthesizing MXene materials for their uses in biomedical and therapeutic applications.

1 citations