Photothermoelectric Research Articles

Self-powered, flexible, and ultrabroadband ultraviolet-terahertz photodetector based on a laser-reduced graphene oxide/CsPbBr3 composite

Self-powered and flexible ultrabroadband photodetectors (PDs) are desirable in a wide range of applications. The current PDs based on the photothermoelectric (PTE) effect have realized broadband photodetection. However, most of them express low photoresponse and lack of flexibility. In this work, high-performance, self-powered, and flexible PTE PDs based on laser-scribed reduced graphene oxide ( LSG ) / CsPbBr 3 are developed. The comparison experiment with LSG PD and fundamental electric properties show that the LSG / CsPbBr 3 device exhibits enhanced ultrabroadband photodetection performance covering ultraviolet to terahertz range with high photoresponsivity of 100 mA/W for 405 nm and 10 mA/W for 118 μm at zero bias voltage, respectively. A response time of 18 ms and flexible experiment are also acquired at room temperature. Moreover, the PTE effect is fully discussed in the LSG / CsPbBr 3 device. This work demonstrates that LSG / CsPbBr 3 is a promising candidate for the construction of high-performance, flexible, and self-powered ultrabroadband PDs at room temperature.

Giant photothermoelectric effect in silicon nanoribbon photodetectors

The photothermoelectric (PTE) effect enables efficient harvesting of the energy of photogenerated hot carriers and is a promising choice for high-efficiency photoelectric energy conversion and photodetection. Recently, the PTE effect was reported in low-dimensional nanomaterials, suggesting the possibility of optimizing their energy conversion efficiency. Unfortunately, the PTE effect becomes extremely inefficient in low-dimensional nanomaterials, owing to intrinsic disadvantages, such as low optical absorption and immature fabrication methods. In this study, a giant PTE effect was observed in lightly doped p-type silicon nanoribbons caused by photogenerated hot carriers. The open-circuit photovoltage responsivity of the device was 3-4 orders of magnitude higher than those of previously reported PTE devices. The measured photovoltage responses fit very well with the proposed photothermoelectric multiphysics models. This research proposes an application of the PTE effect and a possible method for utilizing hot carriers in semiconductors to significantly improve their photoelectric conversion efficiency.

Enhanced Thermoelectric Performance of n-Type Organic Semiconductor via Electric Field Modulated Photo-Thermoelectric Effect.

Modulating photophysical processes is a fundamental way for tuning performance of many organic devices. However, it has not been explored as an effective strategy to manipulate the thermoelectric (TE) conversion of organic semiconductors (OSCs) owing to their critical requirement to carrier concentration (>1018 cm-3 ) and the fact of low exciton separation efficiency in single element OSCs. Here, an electric field modulated photo-thermoelectric (P-TE) effect in an n-type OSC is demonstrated to realize a significant improvement of TE performance. The electrical and spectroscopy characterizations reveal that the electric field gating generates combined modulation of exciton separation, charge screening, and carrier recombination, which produces a more than ten times improvement of photoinduced carrier concentration. These coupled processes contribute to the unconventional Seebeck coefficient (S)-electrical conductivity (σ) trade-off relationship of the photoexcited films, therefore leading to a more than 500% enhancement in the power factor for n-type OTE semiconductors. This work opens a unique way toward state-of-the-art organic P-TE materials for energy harvesting applications.

Ionic Liquid Gating Enhanced Photothermoelectric Conversion in Three-Dimensional Microporous Graphene.

The photothermoelectric (PTE) effect can effectively convert light into electricity through photothermal and thermoelectric processes and has great potential applications in light energy harvesting and bandgap-independent photodetection. It is particularly applicable for the terahertz (THz) range featuring low photon energy but has not been well established due to lack of high-performance PTE materials in this range. Three-dimensional microporous graphene (3DMG) foam possesses ultrahigh THz absorptivity and outstanding photothermal conversion and can serve as a promising candidate. Here, enhancement of the THz PTE response of 3DMG foam by fine-tuning its thermoelectric properties using the ionic liquid electric double layer (EDL) technique was demonstrated. Continuous and reversible control of the Seebeck coefficient of 3DMG highlights the effectiveness of EDL gating in manipulating the electronic structures of such bulk and porous material. An approximate 1 order of magnitude enhancement in the Seebeck coefficient as well as the PTE responsivity was observed. In addition, a double-cell 3DMG EDL device with a p-n junction like channel configuration enabled further improvement of the photoresponse. This work opens a new avenue to optimize the PTE performance of 2D nanosheet-assembled 3D porous materials for highly efficient energy harvesting and detection of THz radiation.

High-quality textured SnSe thin films for self-powered, rapid-response photothermoelectric application

Abstract Tin selenide (SnSe) has attracted great attention in thermoelectrics (TE) thanks to its record high figure of merit (ZT) discovered in single crystal (SC). However, the practical application of SnSe SC is limited due to its extreme growth condition. With the development of flexible integrated electronics, using flexible polycrystalline TE films to substitute rigid SC becomes a main trend. Nevertheless, large resistances of TE films restrict their application as power devices. Here, self-powered SnSe-based photothermoelectric (PTE) detectors are demonstrated. The PTE detectors are sensitive to wide-spectrum and exhibit higher responsivity and respnse speed comparing with SC, due to the small heating volume, small conductive heat flux and large dissipation content of thin films. High-quality (400)-textured SnSe polycrystalline thin films are one-step synthesized by chemical vapor deposition. In-situ in-plane TE measurement shows that the obtained SnSe films possess a dimensionless ZT of 0.15 and a power factor of 0.322 mW m−1 K−2 at 550 K, showing SC level TE performance at low temperatures.

Thermal Localization Enhanced Fast Photothermoelectric Response in a Quasi-One-Dimensional Flexible NbS3 Photodetector.

Ultra-broadband photodetection is crucial for various applications like imaging and sensing and has become a hot research topic in recent years. However, most of the reported ultra-broadband photodetectors can only cover the range from ultraviolet to infrared, which is insufficient. Herein, a photothermoelectric (PTE) detector made of NbS3 is reported. The device shows a considerable performance from ultraviolet to terahertz. For all examined wavelengths, the photoresponsivities are all larger than 1 V W-1 while the response time is less than 10 ms, much shorter than the reported ultra-broadband photodetectors made of millimetric scale graphene, ternary chalcogenide single crystal, and other materials. The extraordinary performance is fully discussed and can be attributed to the thermal localization enhanced PTE effect. Because of the short thermal decay length and low thermal loss, the heat generated by the illumination is localized in only a micrometer scale along the channel, and thus a strong PTE response is produced. In addition, the fabricated device also demonstrates robust flexibility and stability. Thanks to the quasi-one-dimensional (quasi-1D) structure, the NbS3 crystal is easy to be scaled down and thus intrinsically facilitate the integration of detectors. With these favorable merits, the quasi-1D NbS3 crystal holds a promising potential in high-performance, ultra-broadband photodetectors.

Sensitive Terahertz Detection and Imaging Driven by the Photothermoelectric Effect in Ultrashort-Channel Black Phosphorus Devices.

Terahertz (THz) photon detection is of particular appealing for myriad applications, but it still lags behind efficient manipulation with electronics and photonics due to the lack of a suitable principle satisfying both high sensitivity and fast response at room temperature. Here, a new strategy is proposed to overcome these limitations by exploring the photothermoelectric (PTE) effect in an ultrashort (down to 30 nm) channel with black phosphorus as a photoactive material. The preferential flow of hot carriers is enabled by the asymmetric Cr/Au and Ti/Au metallization with the titled‐angle evaporation technique. Most intriguingly, orders of magnitude field‐enhancement beyond the skin‐depth limit and photon absorption across a broadband frequency can be achieved. The PTE detector has excellent sensitivity of 297 V W−1, noise equivalent power less than 58 pW/Hz0.5, and response time below 0.8 ms, which is superior to other thermal‐based detectors at room temperature. A rigorous comparison with existing THz detectors, together with verification by further optical‐pumping and imaging experiments, substantiates the importance of the localized field effect in the skin‐depth limit. The results allow solid understanding on the role of PTE effect played in the THz photoresponse, opening up new opportunities for developing highly sensitive THz detectors for addressing targeted applications.

Large-Area and Broadband Thermoelectric Infrared Detection in a Carbon Nanotube Black-Body Absorber.

Room-temperature mid- and far-infrared photodetectors and energy harvesters meet diverse upcoming demands including health condition monitoring, industrial inspection, and miniaturized power-source for Internet of Things. However, the cryogenic cooling requirement for III-V semiconductors and the inefficient light absorption in two-dimensional (2D) materials, for example, graphene (2.3%) and black phosphorus (∼3%), have hindered mid- and far-infrared optoelectronics from widespread applications. Here, we demonstrate a self-powered infrared photodetector as well as energy harvester via employing vertical photothermoelectric (PTE) effect of a carbon nanotube forest (CNTF). In the self-assembled anti-reflecting CNTF, 99.4% reflection suppression is observed, resulting in a broadband detectivity of 1.9 × 107 cm Hz1/2 in 2.5-25 μm spectral range and peak detectivity of 2.3 × 109 cm Hz1/2 at 4.3 THz via nonlithography fabrication. By virtue of vertical architecture, this photodetector exhibits enhanced sensitivity to weak and unfocused infrared illumination, which mitigates the high actuating power density in conventional PTE or field-effect detectors and renders practical infrared detection in the real life.

Photo-thermoelectric effect induced electricity in stretchable graphene-polymer nanocomposites for ultrasensitive strain sensing

Stretchable strain sensors play an increasingly important role in artificial intelligent devices. However, high-performance strain sensors have been slowly developed owing to the harsh requirement of self-powered function, long cycle life and high resolution. Here, we report a self-powered stretchable graphene-ecoflex composite strain sensor based on photo-thermoelectric (PTE) effect induced electricity. The device exhibits a high strain sensitivity of -0.056 ln(nA)/% with strains ranged from 0% to 20% under 980 nm light illumination, where the strain sensitivity can be found to increase with increasing light intensity. The strain sensor maintains outstanding dynamic stability under periodic strains ranged from 0 to 100% in 100 cycles. The sensing resolution can be as high as 0.5% with both the response and recovery time of less than 0.6 s. It can precisely monitor human joint motions and stretchable strains by implanting the device in pork.

Progress of Photodetectors Based on the Photothermoelectric Effect.

High-performance uncooled photodetectors operating in the long-wavelength infrared and terahertz regimes are highly demanded in the military and civilian fields. Photothermoelectric (PTE) detectors, which combine photothermal and thermoelectric conversion processes, can realize ultra-broadband photodetection without the requirement of a cooling unit and external bias. In the last few decades, the responsivity and speed of PTE-based photodetectors have made impressive progress with the discovery of novel thermoelectric materials and the development of nanophotonics. In particular, by introducing hot-carrier transport into low-dimensional material-based PTE detectors, the response time has been successfully pushed down to the picosecond level. Furthermore, with the assistance of surface plasmon, antenna, and phonon absorption, the responsivity of PTE detectors can be significantly enhanced. Beyond the photodetection, PTE effect can also be utilized to probe exotic physical phenomena in spintronics and valleytronics. Herein, recent advances in PTE detectors are summarized, and some potential strategies to further improve the performance are proposed.

Fast and Sensitive Terahertz Detection Using an Antenna-Integrated Graphene pn Junction.

Although the detection of light at terahertz (THz) frequencies is important for a large range of applications, current detectors typically have several disadvantages in terms of sensitivity, speed, operating temperature, and spectral range. Here, we use graphene as a photoactive material to overcome all of these limitations in one device. We introduce a novel detector for terahertz radiation that exploits the photothermoelectric (PTE) effect, based on a design that employs a dual-gated, dipolar antenna with a gap of ∼100 nm. This narrow-gap antenna simultaneously creates a pn junction in a graphene channel located above the antenna and strongly concentrates the incoming radiation at this pn junction, where the photoresponse is created. We demonstrate that this novel detector has an excellent sensitivity, with a noise-equivalent power of 80 pW/[Formula: see text] at room temperature, a response time below 30 ns (setup-limited), a high dynamic range (linear power dependence over more than 3 orders of magnitude) and broadband operation (measured range 1.8-4.2 THz, antenna-limited), which fulfills a combination that is currently missing in the state-of-the-art detectors. Importantly, on the basis of the agreement we obtained between experiment, analytical model, and numerical simulations, we have reached a solid understanding of how the PTE effect gives rise to a THz-induced photoresponse, which is very valuable for further detector optimization.

Photothermal investigations of phase transitions in liquid thermoelectrics

Two photothermal techniques, the photothermoelectric (PTE) and the photopyroelectric (PPE) were applied to detect first-order phase transitions in some liquid thermoelectric (LTE) material. Due to its large Seebeck coefficient (about 4–5 mV K−1), a LTE based on dodecanol mixed with 10−1 mol L−1 tetrabutylammonium nitrate was selected for investigations. If the PPE method was already largely used to detect phase transitions in various materials belonging to condensed matter, the Seebeck effect, produced by a LTE, is used for the first time as a tool for the detection of phase transitions in the very same material. It was demonstrated that both methods are suitable to detect the first-order phase transitions in LTE materials, but in the case of PTE method the electrical and thermal effects at the phase transition can not be separated, and consequently, it is not possible to derive the critical behavior of the thermal parameters. However, the behavior of the static volume specific heat and dynamic thermal diffusivity, effusivity and conductivity of the investigated LTE could be obtained by using the PPE method in back detection configuration.

Phonon-enhanced photothermoelectric effect in SrTiO3 ultra-broadband photodetector

The self-powered and ultra-broadband photodetectors based on photothermoelectric (PTE) effect are promising for diverse applications such as sensing, environmental monitoring, night vision and astronomy. The sensitivity of PTE photodetectors is determined by the Seebeck coefficient and the rising temperature under illumination. Previous PTE photodetectors mostly rely on traditional thermoelectric materials with Seebeck coefficients in the range of 100 μV K−1, and array structures with multiple units are usually employed to enhance the photodetection performance. Herein, we demonstrate a reduced SrTiO3 (r-STO) based PTE photodetector with sensitivity up to 1.2 V W−1 and broadband spectral response from 325 nm to 10.67 μm. The high performance of r-STO PTE photodetector is attributed to its intrinsic high Seebeck coefficient and phonon-enhanced photoresponse in the long wavelength infrared region. Our results open up a new avenue towards searching for novel PTE materials beyond traditional thermoelectric materials for low-cost and high-performance photodetector at room temperature.

The Role of <i>Pτ</i> in the Photothermoelectric Effect and in Photoredox Catalysis Reactions

Context and Background: Recent research has shown that the amount of energy conserved in light-matter interaction is given by the product of light’s power P times its period τ , i.e. Pτ. To date, evidences of the validity of such finding are restricted to the interaction of light with capacitors, infrared spectroscopy, and vision in vertebrates. Motivation: In this article, we want to explore the validity of the role of Pτ in a broader range of phenomena. Hypothesis: We assume that the photothermoelectric (PTE) effect and photoredox catalysis reactions (PCRs) are manifestations of light-matter interaction and therefore have Pτ conserved in the process. Method: We take the data published in two articles, one on the PTE effect and the other on PCRs and revisit the data analysis of the authors of the original articles considering Pτ as the energy conserved. Results: In the case of the PTE effect, we unveil that the size of the light’s beam cross-sectional area impinging on the photodetectors plays a major role in defining the performance of the photodetectors. With our analysis, the photodetector responsivities actually turn out to be higher than those reported in the original article. In the case of the PCRs, we find that the magnitude of Pτ involved in successful PCRs is independent of the type of light used, whether near-infrared or blue. In addition, the involvement of Pτ in the description of PCRs helps to clarify the role of the law of conservation of energy, which was neglected by the authors of the original article. Conclusions: From this study, we infer that the hypothesis that Pτ that the hypothesis that represents the amount of energy conserved in light-matter interaction is valid and general, useful to measure device performance, and predict alternative processes to achieve desired outcomes.

A Narrowband Photo‐Thermoelectric Detector Using Photonic Crystal

AbstractHere, a wavelength‐specific photo‐thermoelectric (PTE) device is reported that achieves narrowband optical absorption and thermoelectric conversion functions using a stack of thin films on a grating‐patterned substrate. Conventional PTE devices are broadband with the absorption of electromagnetic radiation from ultraviolet to terahertz. There are demands for PTE devices that can exhibit narrowband response at a desired wavelength. Here, the narrowband PTE device consists of a photonic crystal (PC) filter with metal cladding and a thin‐film thermocouple. The PC‐PTE design is investigated numerically to illustrate the underlying energy conversion mechanism. The device is fabricated using nanoreplica molding followed by coating of thin films. The fabricated metal‐cladding PC resonator exhibits a narrowband optical absorption with a resonant absorption coefficient of 85.4% and full‐width‐half‐maximum of 14.8 nm in the visible wavelength range. The PTE measurements show that the thermoelectric output is sensitive to the coupling of incident light and guided‐mode resonance modes. Illuminated under the resonant condition, the PTE device exhibits a responsivity and noise equivalent power of 0.26 V W−1 and 7.5 nW Hz−1/2, respectively. This PC‐PTE technology has the unique attributes of narrowband detection, large surface area, and low cost for the potential application in sensors, optical spectroscopy, and imaging.

Plasmon induced thermoelectric effect in graphene

Graphene has emerged as a promising material for optoelectronics due to its potential for ultrafast and broad-band photodetection. The photoresponse of graphene junctions is characterized by two competing photocurrent generation mechanisms: a conventional photovoltaic effect and a more dominant hot-carrier-assisted photothermoelectric (PTE) effect. The PTE effect is understood to rely on variations in the Seebeck coefficient through the graphene doping profile. A second PTE effect can occur across a homogeneous graphene channel in the presence of an electronic temperature gradient. Here, we study the latter effect facilitated by strongly localised plasmonic heating of graphene carriers in the presence of nanostructured electrical contacts resulting in electronic temperatures of the order of 2000 K. At certain conditions, the plasmon-induced PTE photocurrent contribution can be isolated. In this regime, the device effectively operates as a sensitive electronic thermometer and as such represents an enabling technology for development of hot carrier based plasmonic devices.

A new application of the liquid thermoelectrics: The detection of magnetic phase transitions

During last years, both solid and liquid thermoelectric materials proved to be useful tools for thermal inspection of condensed matter samples. Used in contact techniques, the liquid thermoelectrics are very suitable in investigating the thermal properties of solids, mainly due to the perfect solid sample-liquid sensor thermal contact. The paper proposes a new application of the liquid thermoelectrics (LTE): the detection of phase transitions. In order to prove the suitability of this application, Cr2O3 single crystal was selected as a sample – Cr2O3 is a well-known antiferromagnetic material involved in a phase transition at a Néel temperature around 34 °C. A LTE material (octanol + 10−2 mol/l tetrabutylammonium nitrate (TBAN)) was used as a sensor for the detection of the antiferro-paramagnetic phase transition of Cr2O3. Based on the recently developed theory of the photothermoelectric (PTE) method, the measured amplitude and phase of the complex PTE signal were converted in thermal parameters. As a consequence, the behavior of the static volume specific heat and dynamic thermal diffusivity, conductivity and effusivity of Cr2O3, around the Néel point, have been obtained. A comparison with similar investigations, obtained by using CuCrO2 (a solid thermoelectric materials) as a sensor, was performed. The results obtained with LTE as a sensor proved to be more accurate, due to the previously mentioned “perfect liquid sensor-solid sample” thermal contact.

Photo-thermoelectric Current Enhancement in Graphene-Based Photodetectors Using Plasmonic Nanostructures

A promising way to enhance channel absorption in graphene-based photodetectors is using plasmonic nanostructures. Here, we show that by using metallic nano-gratings on top of the electrodes, an asymmetric hot carrier temperature profile with high intensity along the graphene channel is created. We show that this asymmetric profile creates a photo-thermoelectric (PTE) current even with scenarios like similar contacts materials and uniform Seebeck coefficient along the channel. Our analytical calculations reveal that in the case of normal beam illumination and applying source-drain voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> ), the calculated PTE current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TEP</sub> ) increases considerably. Due to enhanced instructive coupling between plasmonic absorption modes originating from contacts and absorption modes in the channel itself, the proposed photodetector exhibits a maximum responsivity of R = ≈ 800 V/W related to absorbed power.

Photothermoelectric (PTE) characterization of CuCrO2 and Cu4Sn7S16 thermoelectric materials

The recently developed photothermoelectric (PTE) calorimetry was applied to measure the thermal parameters of CuCrO2 and Cu4Sn7S16 thermoelectric materials. Both back and front PTE detection configurations were combined to directly measure the thermal diffusivity and effusivity of the above-mentioned solid thermoelectrics. In the back configuration, CuCrO2 (Seebeck coefficient approximately + 1200 µV K−1) was used as a thermoelectric sensor and CuCrO2 and Cu4Sn7S16 as samples. In the front detection, both CuCrO2 and Cu4Sn7S16 (Seebeck coefficient approximately − 600 µV K−1) materials were alternatively used as sensors, the sample being in this case a thermally thick layer of silicone grease. The proposed combination of configurations eliminates any possible results degeneracy because each fitting procedure involves only one fitting parameter. The results obtained by PTE investigations α CuCrO2 = 1.19 × 10−6 m2 s−1, α Cu4Sn7S16 = 0.33 × 10−6 m2 s−1 and e CuCrO2 = 780 W s1/2 m−2 K−1, e Cu4Sn7S16 = 1358 W s1/2 m−2 K−1 were validated by photopyroelectric (PPE) measurements.

Graphene-based optical photodetector exploiting hybrid plasmonic waveguide to enhance photo-thermoelectric current

A graphene-based optical photodetector with a symmetric hybrid plasmonic waveguide that integrates two high-refractive-index dielectric slabs as a finite-width insulator-metal-insulator (IMI) structure is proposed and investigated at . It is shown that by electrically tuning the graphene refractive index, the gap between the silicon slabs and graphene strip as a hybrid plasmonic waveguide results in modified modal behavior over the graphene layer. This highly lossy hybrid surface plasmon polariton strip mode enhances optical absorption in the graphene channel. An analytical approach reveals that this highly confined absorption creates a highly asymmetric hot-carrier spatial temperature profile along the channel. Based on photo-thermoelectric (PTE) effect, this asymmetric temperature profile along with applied source-drain voltage (Vds) creates a PTE current. Coupled to the super plasmonic mode of hybrid plasmonic waveguide (HPW) mechanism, this photodetector exhibits a maximum responsivity of . In addition, for the proposed HPW graphene photodetector (HPW-GPD), the calculated effective mode area, the propagation length and modal propagation loss are , and , respectively.