Carbon and semiconductor nanoparticles are promising photothermal materials for various solar-driven applications. Inevitable recombination of photoinduced charge carriers in a single constituent, however, hinders the realization of a greater photothermal effect. Core–shell heterostructures utilizing the donor–acceptor pair concept with high-quality interfaces can inhibit energy loss from the radiation relaxation of excited species, thereby enhancing the photothermal effect. Here, core–shell structures composed of a covellite (CuS) shell (acceptor) and spherical carbon nanoparticle (CP) core (donor) (abbreviated as CP/CuS) are proposed to augment the photothermal conversion efficiency via the Förster resonance energy transfer (FRET) mechanism. The close proximity and spectral overlap of the donor and acceptor trigger the FRET mechanism, where the electronic excitation relaxation energy of the CP reinforces the plasmonic resonance and near-infrared absorption in CuS, resulting in boosting the overall photothermal conversion efficiency. CP/CuS core–shell coated on polyurethane (PU) foam exhibits a total solar absorption of 97.1%, leading to an elevation in surface temperature of 61.6 °C in dry conditions under simulated solar illumination at a power density of 1 kW m–2 (i.e., 1 sun). Leveraging the enhanced photothermal conversion emanated from the energy transfer effect in the core–shell structure, CP/CuS-coated PU foam achieves an evaporation rate of 1.62 kg m–2 h–1 and an energy efficiency of 93.8%. Thus, amplifying photothermal energy generation in core–shell structures via resonance energy transfer can be promising in solar energy-driven applications and thus merits further exploration.
more »
« less
This content will become publicly available on June 12, 2025
Photoexcited charge carrier dynamics and electronic properties of two-dimensional MXene, Nb 2 CT x
Two-dimensional, 2D, niobium carbide MXene, Nb2CTx, has attracted attention due to its extraordinarily high photothermal conversion efficiency that has applications ranging from medicine, for tumor ablation, to solar energy conversion. Here, we characterize its electronic properties and investigate the ultrafast dynamics of its photoexcitations with a goal of shedding light onto the origins of its unique properties. Through density functional theory, DFT, calculations, we find that Nb2CTx is metallic, with a small but finite DOS at the Fermi level for all experimentally relevant terminations that can be achieved using HF or molten salt etching of the parent MAX phase, including –OH, –O, –F, –Cl, –Br, –I. In agreement with this prediction, THz spectroscopy reveals an intrinsic long-range conductivity of ∼60 Ω−1 cm−1, with significant charge carrier localization and a charge carrier density (∼1020 cm−3) comparable to Mo-based MXenes. Excitation with 800 nm pulses results in a rapid enhancement in photoconductivity, which decays to less than 25% of its peak value within several picoseconds, underlying efficient photothermal conversion. At the same time, a small fraction of photoinjected excess carriers persists for hundreds of picoseconds and can potentially be utilized in photocatalysis or other energy conversion applications.
more »
« less
- Award ID(s):
- 2021871
- NSF-PAR ID:
- 10523454
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- 2D Materials
- Volume:
- 11
- Issue:
- 3
- ISSN:
- 2053-1583
- Page Range / eLocation ID:
- 035028
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Garnering attention for high conductivity, nonlinear optical properties, and more, MXenes are water-processable 2D materials that are considered candidates for applications in electromagnetic interference shielding, optoelectronic and photonic devices among others. Herein we investigate the intrinsic and photoexcited conductivity in Nb 2 CT x, a MXene with reported high photothermal conversion efficiency. DFT calculations show that hydroxyl and/or fluorine-terminated or is metallic, in agreement with THz spectroscopy, which reveals the presence of free charge carriers that are highly localized over mesoscopic length scales. Photoexcitation of Nb 2 CT x, known to result in rapid heating of the crystal lattice, is found to produce additional free carriers and a transient enhancement of photoconductivity. Most photoexcited carriers decay over the sub-picosecond time scales while a small fraction remain for much longer, sub-nanoseconds, times.more » « less
-
The work proposed here aims to describe the dynamics of photoexcited charge carriers at the interface between the perovskite and electron transport layer (ETL) in perovskite solar cells (PSCs) and the effect that the interface morphology has on these dynamics. This is done in an effort to further develop the understanding of these materials so that their chemical composition and morphology may be better utilized to improve PSCs by means of increasing the power conversion efficiency (PCE), maximizing the chemical stability of PSCs to lengthen their lifespan, finding the cheapest and easiest materials to synthesize which have beneficial properties in photovoltaics, etc. This is done by using density functional theory to model the interface and open system Redfield theory to describe the charge carrier dynamics. We find that the charge transfer characteristics at the perovskite/ETL interface depend greatly on the choice of ligands adsorbed on the ETL that act as a bridge between the perovskite and ETL. The two ligand choices discussed here go so far as to determine whether the system will undergo a Förster energy transfer or a Dexter energy transfer upon photoexcitation.more » « less
-
more » « less
A new record‐high room‐temperature electron Hall mobility (
μ RT = 194 cm2 V−1 s−1atn ≈ 8 × 1015 cm−3) for β‐Ga2O3is demonstrated in the unintentionally doped thin film grown on (010) semi‐insulating substrate via metal‐organic chemical vapor deposition (MOCVD). A peak electron mobility of ≈9500 cm2 V−1 s−1is achieved at 45 K. Further investigation on the transport properties indicates the existence of sheet charges near the epilayer/substrate interface. Si is identified as the primary contributor to the background carrier in both the epilayer and the interface, originating from both surface contamination and growth environment. The pregrowth hydrofluoric acid cleaning of the substrate leads to an obvious decrease in Si impurity both at the interface and in the epilayer. In addition, the effect of the MOCVD growth condition, particularly the chamber pressure, on the Si impurity incorporation is studied. A positive correlation between the background charge concentration and the MOCVD growth pressure is confirmed. It is noteworthy that in a β‐Ga2O3film with very low bulk charge concentration, even a reduced sheet charge density plays an important role in the charge transport properties. -
We report on the free charge carrier properties of a two-dimensional electron gas (2DEG) in an AlN/Al x Ga 1– x N high electron mobility transistor structure with a high aluminum content ( x = 0.78). The 2DEG sheet density [Formula: see text] cm −2 , sheet mobility [Formula: see text] cm 2 /(Vs), sheet resistance [Formula: see text] [Formula: see text], and effective mass [Formula: see text] at low temperatures [Formula: see text] are determined by terahertz (THz) optical Hall effect measurements. The experimental 2DEG mobility in the channel is found within the expected range, and the sheet carrier density is in good agreement with self-consistent Poisson–Schrödinger calculations. However, a significant increase in the effective mass of 2DEG electrons at low temperatures is found in comparison with the respective value in bulk Al 0.78 Ga 22 N ([Formula: see text]). Possible mechanisms for the enhanced 2DEG effective mass parameter are discussed and quantified using self-consistent Poisson–Schrödinger calculations.more » « less
