Transparent all-oxide photovoltaics and broadband high-speed energy-efficient optoelectronics

Patel, Malkeshkumar,Ban, Dong-Kyun,Ray, Abhijit,Kim, Joondong Elsevier 2019 Solar energy materials and solar cells Vol.194 No.-

<P><B>Abstract</B></P> <P>Heterostructure of wide-bandgap materials have great potential for use in transparent optoelectronics for examples ultraviolet photodetectors, transparent solar cells, and transparent electronics. This study demonstrates the exciton, band-to-band and intermediate-band optical transitions in a ZnO/NiO heterostructure at room temperature. This heterostructure exhibits Ohmic current-voltage characteristics close to that of various metal contacts such as Ag, C, Ni, and Au. Temperature-dependence studies revealed that the open-circuit voltage (V<SUB>OC</SUB>) of ZnO/NiO heterostructure is limited by the charge-transfer potential, analogous to excitonic solar cells. A negligibly small dark current of 1.6 × 10<SUP>−8</SUP> A, a large V<SUB>OC</SUB> of 675 mV and a photoresponse speeds of 9.4 μs make it promising for high-speed energy-efficient optoelectronics. The optoelectronic performances of the ZnO/NiO/Ag microink suggest that broadband photons can be utilized with incident photons to current conversion efficiencies (IPCEs) of 2% and 39% in the visible and ultraviolet regions, respectively which demonstrate that the ZnO/NiO heterostructure can acts as a broadband quantum optoelectronic device.</P> <P><B>Highlights</B></P> <P> <UL> <LI> All transparent oxide photovoltaic is realized by ZnO/NiO heterostructure. </LI> <LI> Optical transitions found in a ZnO/NiO heterostructure at room temperature. </LI> <LI> ZnO/NiO heterostructure can acts as a broadband quantum optoelectronic device. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Suppression of the Hybridization of Surface States and Transport Property in Ultrathin Bi2Se3/graphene Heterostructure

채지민,Seoung-Hun Kang,권영균,조만호 한국진공학회 2019 Applied Science and Convergence Technology Vol.28 No.6

Topological insulators (TIs) have gained considerable attention owing to their topologically protected helical edge states called topological surface states. To employ TIs, it is necessary to reduce film thickness and suppress effects from the bulk carrier. When the film thickness is less than 5 quintuple layers (QLs), the top and bottom surface states overlap, thereby increasing surface bandgap. In this study, we investigate the suppression of the hybridization of surface states in a 3-QL Bi2Se3/graphene heterostructure. In the 3-QL Bi2Se3 film grown on graphene, surface states affected by strain, and band bending effects from graphene are localized to the top and bottom and possess a closed bandgap. Further, we investigated transport properties in the 3-QL Bi2Se3/graphene heterostructure and verified the independent transport channels of Bi2Se3 and graphene, and the long coherence length of 534 nm. In conclusion, the closed bandgap and long coherence length in the 3-QL Bi2Se3/graphene heterostructure implies that the proximity effect in a TI/non-TI heterostructure can be attractive for future applications, beyond the physical and topological thickness limit.

Suppression of the Hybridization of Surface States and Transport Property in Ultrathin Bi₂Se₃/graphene Heterostructure

Jimin Chae,Seoung-Hun Kang,Young-Kyun Kwon,Mann-Ho Cho 한국진공학회(ASCT) 2019 Applied Science and Convergence Technology Vol.28 No.6

Topological insulators (TIs) have gained considerable attention owing to their topologically protected helical edge states called topological surface states. To employ TIs, it is necessary to reduce film thickness and suppress effects from the bulk carrier. When the film thickness is less than 5 quintuple layers (QLs), the top and bottom surface states overlap, thereby increasing surface bandgap. In this study, we investigate the suppression of the hybridization of surface states in a 3-QL Bi₂Se₃/graphene heterostructure. In the 3-QL Bi₂Se₃ film grown on graphene, surface states affected by strain, and band bending effects from graphene are localized to the top and bottom and possess a closed bandgap. Further, we investigated transport properties in the 3-QL Bi₂Se₃/graphene heterostructure and verified the independent transport channels of Bi₂Se₃ and graphene, and the long coherence length of 534 nm. In conclusion, the closed bandgap and long coherence length in the 3-QL Bi₂Se₃/graphene heterostructure implies that the proximity effect in a TI/non-TI heterostructure can be attractive for future applications, beyond the physical and topological thickness limit.

Interfacial properties of van der Waals lead iodide /graphene heterostructure

한수민,신내철 한국공업화학회 2020 한국공업화학회 연구논문 초록집 Vol.2020 No.-

Van der Waals (vdW) type heterostructures based on 2D layered crystals are attractive for various applications including electronics and optoelectronics owing to their structure-dependent properties. Lead iodide (PbI₂), a vdW-type crystalline material is a promising candidate for photodetector applications. Especially, an enhanced photodetecting performance is expected from PbI₂/graphene vdW heterostructure. It is of particular importance to prepare PbI₂/graphene heterostructure in controllable manner to maximize the device capability. Here, we demonstrate selective PbI₂ growth on graphene monolayers via chemical vapor deposition. Systematic comparison of PbI₂ domain morphologies grown on various substrates coupled with conductive AFM measurement suggests that the interfacial energy between the substrate (i.e., graphene) and PbI₂ plays a key role in the fabrication of vdW heterostructure. This result provides fundamental perspective for the optimization of vdW heterostructure.

A comparative study of the mechanical properties of multilayer MoS2 and graphene/MoS2 heterostructure: effects of temperature, number of layers and stacking order

Nayereh Ghobadi 한국물리학회 2017 Current Applied Physics Vol.17 No.11

In this paper molecular dynamic simulation is used to examine the mechanical properties of multilayer molybdenum disulfide (MoS2) and graphene/MoS2 heterostructure under uniaxial tensile and normal compressive strain. The effects of temperature, layer number and stacking order of layers on the stressstrain curve and elastic properties are studied. We find that the Young's modulus and vertical elastic constant of the heterostructure are much larger than that of MoS2 which is due to the higher stiffness and Young's modulus of graphene compared to MoS2. Furthermore, the results reveal that graphene/ MoS2 heterostructure is more resistant to the variation of temperature. While the rise in temperature results in the decrease of elastic constants, fracture strain and fracture stress of both structures, the increase in the number of layers only affects the elastic properties of heterostructure and has little influence on the stiffness of multilayer MoS2. Our simulations also illustrate that the highest energy stacking orders, AA3 and AB3, wherein S atoms of top layer are located above the S atoms of bottom layer, have the lowest elastic constants among all structures.

Tunable Electrical and Optical Characteristics in Monolayer Graphene and Few-Layer MoS₂ Heterostructure Devices

Rathi, Servin,Lee, Inyeal,Lim, Dongsuk,Wang, Jianwei,Ochiai, Yuichi,Aoki, Nobuyuki,Watanabe, Kenji,Taniguchi, Takashi,Lee, Gwan-Hyoung,Yu, Young-Jun,Kim, Philip,Kim, Gil-Ho American Chemical Society 2015 NANO LETTERS Vol.15 No.8

<P>Lateral and vertical two-dimensional heterostructure devices, in particular graphene-MoS2, have attracted profound interest as they offer additional functionalities over normal two-dimensional devices. Here, we have carried out electrical and optical characterization of graphene-MoS2 heterostructure. The few-layer MoS2 devices with metal electrode at one end and monolayer graphene electrode at the other end show nonlinearity in drain current with drain voltage sweep due to asymmetrical Schottky barrier height at the contacts and can be modulated with an external gate field. The doping effect of MoS2 on graphene was observed as double Dirac points in the transfer characteristics of the graphene field-effect transistor (FET) with a few-layer MoS2 overlapping the middle part of the channel, whereas the underlapping of graphene have negligible effect on MoS2 FET characteristics, which showed typical n-type behavior. The heterostructure also exhibits a strongest optical response for 520 nm wavelength, which decreases with higher wavelengths. Another distinct feature observed in the heterostructure is the peak in the photocurrent around zero gate voltage. This peak is distinguished from conventional MoS2 FETs, which show a continuous increase in photocurrent with back-gate voltage. These results offer significant insight and further enhance the understanding of the graphene-MoS2 heterostructure.</P>

Wafer-Scale van der Waals Heterostructures with Ultraclean Interfaces via the Aid of Viscoelastic Polymer

Boandoh, Stephen,Agyapong-Fordjour, Frederick Osei-Tutu,Choi, Soo Ho,Lee, Joo Song,Park, Ji-Hoon,Ko, Hayoung,Han, Gyeongtak,Yun, Seok Joon,Park, Sehwan,Kim, Young-Min,Yang, Woochul,Lee, Young Hee,Kim, American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.1

<P>Two-dimensional (2D) van der Waals (vdW) heterostructures exhibit novel physical and chemical properties, allowing the development of unprecedented electronic, optical, and electrochemical devices. However, the construction of wafer-scale vdW heterostructures for practical applications is still limited due to the lack of well-established growth and transfer techniques. Herein, we report a method for the fabrication of wafer-scale 2D vdW heterostructures with an ultraclean interface between layers via the aid of a freestanding viscoelastic polymer support layer (VEPSL). The low glass transition temperature (<I>T</I><SUB>g</SUB>) and viscoelastic nature of the VEPSL ensure absolute conformal contact between 2D layers, enabling the easy pick-up of layers and attaching to other 2D layers. This eventually leads to the construction of random sequence 2D vdW heterostructures such as molybdenum disulfide/tungsten disulfide/molybdenum diselenide/tungsten diselenide/hexagonal boron nitride. Furthermore, the VEPSL allows the conformal transfer of 2D vdW heterostructures onto arbitrary substrates, irrespective of surface roughness. To demonstrate the significance of the ultraclean interface, the fabricated molybdenum disulfide/graphene heterostructure employed as an electrocatalyst yielded excellent results of 73.1 mV·dec<SUP>-1</SUP> for the Tafel slope and 0.12 kΩ of charge transfer resistance, which are almost twice as low as that of the impurity-trapped heterostructure.</P> [FIG OMISSION]</BR>

Effect of directional light dependence on enhanced photoelectrochemical performance of ZnIn₂S₄/TiO₂ binary heterostructure photoelectrodes

David, Selvaraj,Mahadik, Mahadeo A.,An, Gil Woo,Ryu, Jungho,Kim, Hyun Gyu,Jang, Jum Suk Elsevier 2018 ELECTROCHIMICA ACTA Vol.276 No.-

<P><B>Abstract</B></P> <P>This work focuses on dependence of incident light illumination direction on the photoelectrochemical performance of hydrothermally prepared two dimensional ZnIn<SUB>2</SUB>S<SUB>4</SUB> nanosheets/one dimensional rutile TiO<SUB>2</SUB> nanorod arrays (2D ZIS NS's/1D R-TNR's) heterostructure photoelectrodes. The 2D ZIS NS's are grown on the 1D R-TNR's/FTO substrates by varying the concentration of ZIS precursor in the hydrothermal method, forming 2D ZIS NS's/1D R-TNR's heterostructure. One dimensional rutile TiO<SUB>2</SUB> nanorod arrays (1D R-TNR's) provide excellent electron transfer pathway and role of the 2D ZIS NS's is to offer effective visible light absorbing surface onto the 1D R-TNR's and extended the absorbance spectrum from ultraviolet to visible region; bathochromic shift occurs. This binary heterostructure provides the lower resistance, shortest electron transport time and less recombination under the back side illumination (BSI) and effectively contributed to charge separation and transport in 2D ZIS NS's/1D R-TNR's heterostructure. However, the results demonstrate that the front side illumination (FSI) results in poor PEC performance; because of blockage of light at the surface of 2D ZIS NS's. Further, these results show that BSI could also be applicable for other heterostructures, where the low band gap sulfide materials need to be engineered on large band gap metal oxide for energy harvesting in future prospect.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of tailoring of ZIS precursor concentration on PEC performance is discussed. </LI> <LI> The dependence of photocurrent on the incident light direction was studied. </LI> <LI> BSI enables high light penetration, short transit time, and improved photocurrent. </LI> <LI> Optimized ZIS/1D TNR showed higher photocurrent density (<I>J</I> <SUB>ph</SUB>) (∼1.6 mA cm<SUP>−2</SUP>) for BSI over FSI(∼0.793 mA cm<SUP>−2</SUP>). </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The surfactant free hydrothermally prepared binary heterojunction photoanode to boost up the electron/hole pairs in short transit time under the backside irradiation.</P> <P>[DISPLAY OMISSION]</P>

Electron Tunneling Enhancement in MoS2/Hexagonal Boron Nitride/Multilayer Graphene Heterostructures by Bubble Formation

권오훈,장서균,김종윤,Han Seul Kim,유영준 한국진공학회 2022 Applied Science and Convergence Technology Vol.31 No.5

Unintentional bubbles are formed when manufacturing devices using two-dimensional materials. Usually, these bubbles affect device performance degradation, but in the case of memory devices, an additional charge trap can be expected. We investigate the direct surface potential of bubbles formed in a hexagonal boron nitride (hBN)/multilayer graphene (MLG) heterostructure. Specifically, we study the electron transfer improvement by increasing the memory window of a MoS2/hBN/MLG heterostructure in floating gate memory owing to bubbles formed at the hBN/MLG heterointerface. This characterization of bubbles containing molecules such as water or hydrocarbon in two-dimensional material heterointerfaces can promote the understanding of charge carrier tunneling in two-dimensional material heterostructures.

태양광 물 분해를 통한 수소 생산용 Cu₂O/CuO 이종접합 광전극의 제작 및 광전기화학적 특성

김소영,김효진,홍순구,김도진,Kim, Soyoung,Kim, Hyojin,Hong, Soon-Ku,Kim, Dojin 한국재료학회 2016 한국재료학회지 Vol.26 No.11

We report on the fabrication and characterization of a novel $Cu_2O/CuO$ heterojunction structure with CuO nanorods embedded in $Cu_2O$ thin film as an efficient photocathode for photoelectrochemical (PEC) solar water splitting. A CuO nanorod array was first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method; then, a $Cu_2O$ thin film was electrodeposited onto the CuO nanorod array to form an oxide semiconductor heterostructure. The crystalline phases and morphologies of the heterojunction materials were examined using X-ray diffraction and scanning electron microscopy, as well as Raman scattering. The PEC properties of the fabricated $Cu_2O/CuO$ heterojunction photocathode were evaluated by photocurrent conversion efficiency measurements under white light illumination. From the observed PEC current density versus voltage (J-V) behavior, the $Cu_2O/CuO$ photocathode was found to exhibit negligible dark current and high photocurrent density, e.g. $-1.05mA/cm^2$ at -0.6 V vs. $Hg/HgCl_2$ in $1mM\;Na_2SO_4$ electrolyte, revealing the effective operation of the oxide heterostructure. The photocurrent conversion efficiency of the $Cu_2O/CuO$ photocathode was estimated to be 1.27% at -0.6 V vs. $Hg/HgCl_2$. Moreover, the PEC current density versus time (J-T) profile measured at -0.5 V vs. $Hg/HgCl_2$ on the $Cu_2O/CuO$ photocathode indicated a 3-fold increase in the photocurrent density compared to that of a simple $Cu_2O$ thin film photocathode. The improved PEC performance was attributed to a certain synergistic effect of the bilayer heterostructure on the light absorption and electron-hole recombination processes.