Insertion Of Interlayer Research Articles

Influence of tin oxide (SnO2) interlayer on the electrical and reverse current conduction mechanism of Au/n-InP Schottky junction and its microstructural properties

The microstructural and current-voltage (I-V) characteristics of the prepared Au/SnO2/n-InP heterojunction (HJ) with an e-beam evaporated tin oxide (SnO2) film as an interlayer between the Au and InP substrate have been explored. The X-Ray diffraction and transmission electron microscopy results confirm the formation of the SnO2 thin film on InP surface. Then, the Au/SnO2/n-InP HJ diode is prepared and explored its electrical properties by the I-V approach. Low reverse leakage current is noted for HJ diode than the Au/n-InP Schottky junction (SJ). Higher barrier height (BH) is attained for the HJ compared to the SJ, which indicates that the insertion of SnO2 interlayer leads to an increase in the BH of SJ. Further, the BH is evaluated for the SJ and HJ diodes by Hernandez and Cheung's methods and matched with one another. Results exhibit that the interface state density (NSS) of HJ is less than the SJ, suggesting that the use of the SnO2 layer plays a key role in reducing NSS. Analysis of the reverse leakage current transport suggested the dominance of Poole-Frenkel emission in the lower bias region while the Schottky emission mechanism governs at upper bias region in both the SJ and HJ diodes. These results could provide expedient information of SnO2 interlayer for the design of metal/interlayer/semiconductor or heterojunction devices.

(Invited) Fabrication and Characterization of Ge-Based MIS Structures

Germanium (Ge) is a very attractive channel material for future high-performance metal-insulator-semiconductor (MIS) devices because it exhibits much higher low-field electron (two times higher) and hole (four times higher) mobilities than Si. In addition, the smaller band gap of Ge than that of Si should allow the further reduction of power consumption in advanced integrated circuits and the lower melting point of Ge than that of Si also enables Ge-based device integration at low processing temperatures. However, until the early years of the 2000s, the reported electrical properties of high-k/Ge interfaces had been so poor that one of the critical issues in establishing Ge-based MIS technology was the effective passivation of Ge surfaces by dielectrics with superior interface properties. Although the quality of the Ge-MIS structure has been remarkably improved in the past decade, the relationship between the processing methods and the quality has not been discussed precisely.In this paper, we report on the fabrication of Ge MIS structures with various high-k dielectric materials and interlayer materials through various methods. We also introduce the convenient method to characterize the interface trap densities (Dit's) of the MIS capacitors by spectroscopic measurement of the interface trap density in an insulator/Ge interface at room temperature [1]. The effects of the insertion of interlayers into the interface of high-k insulator/Ge and the application of heat treatment to the Ge MIS structures will be also presented.For instance, the Dit of Ta2O5/GeNx/Ge fabricated by electron-cyclotron-resonance (ECR) plasma nitridation and sputtering was estimated to be 4×1011 cm-2 · eV-1 [2], that of Si3N4/GeNx/Ge by ECR plasma nitridation to be 1×1011 cm-2 · eV-1 [3-6], and that of Al2O3/GeO2/Ge by ECR plasma oxidation and sputtering to be 4.5×1010 cm-2 · eV-1 [7-9]. These results have summarized that the adequate surface preparations of the interfaces and films by the ECR plasma process with low energy plasma irradiation have been effective to realize the low Dit of MIS structures with GeO2 and/or GeNx.These results have expanded to another MIS structures fabricated by more conventional film formation technique such as the atomic layer deposition (ALD) and the radio frequency (RF) magnetron sputtering. The Dit of Al2O3/Al germanate/Ge by ALD with trimethylaluminum (TMA) and microwave-generated atomic oxygen was estimated to be 2×1011cm-2 · eV-1 [10], and that of HfO2/Ge by RF magnetron sputtering to be 5.9×1011 cm-2 · eV-1. These results have summarized that the heat treatment after the fabrication of MIS strucures have affected interface properties of germanate/Ge and oxide/Ge.Although the mechanism by which the process conditions act on the interface state is now under estimation, it has been speculated that the fabrication method, the insertion of the interlayers, and the application of heat treatment have a great influence on the interface characteristics. The structures and the fabrication method of various MIS will be discussed.Part of this work was carried out under the Cooperative Research Project Program of the Research Institute of Electrical Communication, Tohoku University.

Effects of Brass Interlayer on Mechanical Properties of Friction Stir Welded AA 6061-T6 Joint

The most important issues in the joining of similar aluminum alloy are softening of weld zone and reduction in tensile strength of joints. Use of a metallic interlayer can resolve these issues. In the present research work, effect of brass interlayer on the properties of friction stir welded 6061-T6 aluminum alloy was studied. X-ray diffraction analysis was carried out to investigate the phase composition with brass interlayer. Al2Cu and Al4Cu9 intermetallic compounds were formed at the welded zone. Mechanical properties were examined through the tensile and microhardness testing. Tensile test results reveal that the use of brass interlayer is a good solution to improve the joint strength, as the insertion of brass interlayer enhances the joint strength up to 36%. In addition, use of brass interlayer enhances the microhardness at the weld zone and the softening issue has been resolved to some extent. Field emission scanning electron microscopy was used to investigate the mechanism of fracture behavior in fractured tensile specimens. However, insertion of brass interlayer slightly changes the ductile fracture toward brittle fracture.

Strain-resilient electrical functionality in thin-film metal electrodes using two-dimensional interlayers.

Flexible electrodes that allow electrical conductance to be maintained during mechanical deformation are required for the development of wearable electronics. However, flexible electrodes based on metal thin-films on elastomeric substrates can suffer from complete and unexpected electrical disconnection after the onset of mechanical fracture across the metal. Here we show that the strain-resilient electrical performance of thin-film metal electrodes under multimodal deformation can be enhanced by using a two-dimensional (2D) interlayer. Insertion of atomically-thin interlayers — graphene, molybdenum disulfide, or hexagonal boron nitride — induce continuous in-plane crack deflection in thin-film metal electrodes. This leads to unique electrical characteristics (termed electrical ductility) in which electrical resistance gradually increases with strain, creating extended regions of stable resistance. Our 2D-interlayer electrodes can maintain a low electrical resistance beyond a strain in which conventional metal electrodes would completely disconnect. We use the approach to create a flexible electroluminescent light emitting device with an augmented strain-resilient electrical functionality and an early-damage diagnosis capability.

An N-type Naphthalene Diimide Ionene Polymer as Cathode Interlayer for Organic Solar Cells

Polymer solar cells (PSCs) based on non-fullerene acceptors have the advantages of synthetic versatility, strong absorption ability, and high thermal stability. These characteristics result in impressive power conversion efficiency values, but to further push both the performance and the stability of PSCs, the insertion of appropriate interlayers in the device structure remains mandatory. Herein, a naphthalene diimide-based cathode interlayer (NDI-OH) is synthesized with a facile three-step reaction and used as a cathode interlayer for fullerene and non-fullerene PSCs. This cationic polyelectrolyte exhibited good solubility in alcohol solvents, transparency in the visible range, self-doping behavior, and good film forming ability. All these characteristics allowed the increase in the devices’ power conversion efficiencies (PCE) both for fullerene and non-fullerene-based PSCs. The successful results make NDI-OH a promising cathode interlayer to apply in PSCs.

A review on friction stir welding: A sustainable way of manufacturing

Abstract Friction stir welding (FSW) process has gained popularity due to its energy efficiency in joining similar or dissimilar materials as compared to traditional way of joining materials and as it involves no use of shielding gas and little harmful emissions due to which it is regarded as ‘green technology’. It’s a solid-state joining process in which plastic deformation takes place to join the similar or dissimilar materials rather than melting. Due to this its applications can be found in the field of industries ranging from aerospace to ship building and rail to electronics. FSW plays a key role in joining many ‘non-weldable’ aluminium alloys such as from 2xxx series alloys (Al-Cu) and 7xxx series alloys (Al-Zn) which is not possible with conventional process leads to softening of weld plates which leads to decrease in the mechanical properties. Hence, the study of various interlayers such as zinc, copper, brass, nickel, tin etc. has become a hot topic for researchers. The joining of dissimilar material is often difficult due to difference in physical properties and composition and hence use of interlayer in FSW helps in effective joining. Insertion of interlayer between the interface of plates to be joined not only enhances the tensile strength of the weld joint but also restricts the excessive formation of hard and brittle intermetallic compounds (IMCs) and leads to controlled formation of fine and uniformly distribution of IMCs and reduces the residual stresses and further increases the joint efficiency. This work contains the review of some important research papers on FSW of similar alloys (Al-Al), dissimilar alloys (Al-Mg), and effects of interlayer on similar alloys (Al/Cu/Al) and dissimilar alloys (Al/Zn/Mg). This paper also throws light on effects of process parameters such as (tool rotation, tool transverse speed, tool materials) on joining of materials by FSW has been discussed along with the suggestions of the researchers.

Non-invasively improving the Schottky barrier of MoS2/metal contacts by inserting a SiC layer.

The applications of two-dimensional (2D) materials in electronics, optoelectronics, and spintronics are limited by the high contact resistance at the metal/semiconductor interface owing to the strong Fermi-level pinning. In this study, an interlayer insertion strategy is proposed to solve this problem, and first principles calculations are done to study the influences of inserting a SiC layer on the Schottky barrier and electronic properties of MoS2/metals (Mg, Al, In, Cu, Ag, Au, Pd, Ti, and Sc). The average charge value substantially increased (≥0.060 e) at the interface between SiC and MoS2 layers, and then no tunneling barrier appeared except for the MoS2/Au contact by inserting the SiC layer. Moreover, ΦSB,N almost decreases for the MoS2/metal contacts by inserting the SiC layer. When Ti, Cu, Au, and Pd are used as electrodes, the n-type Schottky barrier is formed with the ΦSB,N values of 0.479 eV, -0.073 eV, 0.498 eV, and 0.225 eV, respectively. However, if Al, In, Mg, and Ag are used as electrodes, the systems are transformed into Ohmic contact. These findings provide a practical guideline for depinning the Fermi level at contact interfaces and designing the high performance TMD-based nanoelectronic devices.

Enhancement of Electrochemical Performance of All-Solid-State Lithium‐Ion Thin-Film Batteries By Interface Modification with Al2O3 Interlayer

IntroductionAll-solid-state lithium-ion thin-film battery is one of the promising candidates for next-generation battery systems. However, the low Li-ion conductivity of solid electrolytes and the considerable electrolyte/electrode interface resistance greatly hamper the commercialization of all-solid-state thin-film Li-ion batteries. In this study, we fabricate the all-solid-state lithium-ion thin-film battery using V2O5 electrode and LiPON solid electrolyte. And we introduce Al2O3 interlayer between the Li metal and LiPON solid electrolyte to decrease the interfacial resistance.ExperimentalThe Cathode (V2O5), the solid electrolyte (LiPON) and the interlayer (Al2O3) were prepared on Ti/Pt-coated Si substrates by RF sputtering system. In addition, The Li anode and the Cu current collector were deposited by thermal evaporation. The thicknesses of the V2O5 and LiPON thin films were approximately 100 and 500 nm, respectively. To evaluate the electrochemical properties, 2032-type coin cells were assembled in an argon-filled glove box. Charge/Discharge tests were carried out at various C rates from 0.5 to 100 C with cutoff voltages of 2 and 4 V. Electrochemical impedance spectroscopy was conducted in the frequency range of 100 KHz – 1 Hz with a sinus amplitude voltage of 10 mV.Results and DiscussionThe XRD results of the V2O5 and LiPON thin film shows the amorphous structure. The Charge/Discharge profiles shows typical curves of amorphous V2O5 electrode. The rate capability results show that the insertion of Al2O3 interlayer between the Li metal and the LiPON solid electrolyte sample enhanced the rate performance. Also, The TEM cross-section image results demonstrate that Al2O3 interlayer improves the adhesion to Li metal on LiPON solid electrolyte. These results indicate that as the adhesion between Li metal and LiPON solid electrolyte is improved, electrochemical performance is improved in all-solid-state lithium-ion thin-film batteries.ConclusionsWe successfully fabricated the all-solid-state lithium-ion thin-film battery using the amorphous V2O5 electrode and LiPON solid electrolyte. In addition, through the insertion of Al2O3, the interface between LiPON and Li became uniform and the electrochemical properties were improved. In other words, the interfacial control between solid electrolyte and Li metal is a key factor for the improvement of the electrochemical properties of all-solid-state lithium-ion thin-film batteries.

Repeated loading of soilbag-reinforced road subgrade

Soilbags are three-dimensional soil-confining units used in road foundations. This paper uses vertical repeated loading tests to investigate the performance of soilbags as reinforcement in road subgrades as well as the influence of such factors as the frequency and amplitude of loading, the number of reinforcement layers, and the buried depth of the soilbag reinforcement. The results show that soilbags as reinforcement are effective at reducing permanent and resilient deformations of the road subgrade as well as vibrations caused by traffic loads. The soilbags as reinforcement perform better when the number of soilbag-reinforced layers is increased. More than two layers of soilbags are needed to reinforce the road subgrade to make efficient use of the effect of interlayer insertion between soilbags. Furthermore, a thin surface soil cover is desirable to spread the applied pressure more effectively over the soilbags and level the subgrade.

A graphene-silicon Schottky photodetector with graphene oxide interlayer

A photodetector based on graphene-silicon Schottky diode with graphene oxide (GO) interlayer was prepared in this research. The GO interlayer suppressed the dark current, and increased the photocurrent 2.73 times. With the reverse bias of 2 V, the responsivity of Gr/GO/n-Si Schottky photodiode was 0.65 A/W under 633 nm illumination, meanwhile the ON/OFF ratio reaches 2.73 × 105 due to the insertion of GO interlayer. The characterization of photoelectric properties showed stable photo sensing performance with the increase of bias voltage and incident light power. The response time and recovery time were 1 ms, which indicated that the response speed of graphene-silicon Schottky photodiode was well preserved after inserting GO interlayer.

Microstructure and mechanical properties of W/steel joints diffusion bonded with Nb and Nb/Ni interlayers by spark plasma sintering

Tungsten/steel joints are desired for fusion reactors and militarily applications, as it could combine the unique properties of these two dissimilar metals. In view of the large differences of physical and chemical properties between W and steel, diffusion bonding is considered to be the proper technique for joining of W to steel. In this paper, diffusion bonding of W to low activation ferritic/martensitic steel at 1050 °C with 50 MPa for 20 min by spark plasma sintering (SPS) were investigated. The results showed that direct diffusion bonding of W to steel was feasible. However, the formation of ferrite and carbide at the W/steel interface lowered the joint strength. Effects of the insertion of ductile interlayers (Nb, Nb/Ni) on the joining interface microstructure and mechanical properties of W/steel joints were studied. The detailed microstructural characterization revealed that Nb could prevent the formation of ferrite and carbide at the W/steel interface. The Ni promoted the interfacial diffusion between Nb and steel. The shear strength and Vickers hardness of the joints were evaluated.

Ultrahigh “Relative Energy Density” and Mass Loading of Carbon Cloth Anodes for K-Ion Batteries

Mass loading and potential plateau are the two most important issues of potassium (K)-ion batteries (KIBs), but they have long been ignored in previous studies. Herein, we report a simple and scala...

Interlayer effect on photoluminescence enhancement and band gap modulation in Ga-doped ZnO thin films

Nano-dimensional ZnO have drawn much attention due to its wonderful transmittance , high UV emission, better environmental and thermal stability, abundant resources and low price for use in many advanced applications. In this context, here we report photoluminescence and structural properties of Ga-doped ZnO thin films , synthesized using pulsed laser deposition . The profound effect of Au and Ag as interlayer on Ga-doped ZnO thin films has been presented systematically. The crystalline texture of the grown films was properly oriented along (002) lattice planes with hexagonal wurtzite structure as determined by X-ray diffraction analysis. Surface study was carried out by means of field emission scanning electron microscope revealing low roughness on surface of the films. These films reveal an enhancement of twofold photoluminescence behavior in the near band edge emission region with the insertion of metallic interlayer. The band gap energies of the films obtained were 3.29–3.52 eV using IR spectrophotometer . Reflectance spectra reveal less reflectance (<16%) and more absorption in the UV-NIR region which provide a novel way to replace other UV and IR photodetectors with Ga-doped ZnO. • Synthesis of pulsed laser deposited highly crystalline Ga-doped ZnO thin films. • Utility of Au and Ag as buffer layers between Ga-doped ZnO thin films. • Smooth surface and grain morphology were obtained. • Dominance of quantum confinement in enhancing near band edge luminescence spectra.

Mo-interlayer-mediated thermal conductance at Cu/diamond interface measured by time-domain thermoreflectance

The interfacial thermal conductance (G) in Cu/diamond composites is generally determined by a deduction from thermal conductivity measurement of the composites. In this article, we prepare a Cu/Mo/diamond sandwich structure by magnetron sputtering to directly measure G between Cu and diamond using time-domain thermoreflectance and to probe the effect of the interlayer on G. The interlayer is tuned to a 105 nm-thick Mo layer on a 5 nm-thick Mo2C layer, to a full Mo2C layer, and to a Mo2C layer on a mixed Mo2C and fullerene layer with annealing temperature. The partial conversion of Mo interlayer benefits the thermal transport between Cu and diamond and a maximum G value of 132 MW m−2 K−1 is obtained for the case of 105 nm-thick Mo layer on 5 nm-thick Mo2C layer. This study highlights the importance of appropriate interlayer insertion to mediate thermal transport at Cu/diamond interface for thermal management applications.

The effect of graphene interlayer at Pt/YIG interface on spin pumping

Spin pumping and the spin transfer torque in the normal metal (NM)/ferromagnetic materials (FM) heterostructure strongly depend on the interfacial spin memory loss. Therefore, the interface engineering of the NM/FM bilayer is important for enhancing spin pumping and spin-orbit torque efficiency for spin-orbitronic devices.In this study, we investigate the influence of the graphene interlayer between Pt and yttrium iron garnet (YIG) on spin pumping. Measurements of both the coplanar wave guide ferromagnetic resonance and inverse spin Hall effect with ferromagnetic resonance are performed to study the role of graphene in the transmission of the spin current at the interface. Results indicate a decreased Gilbert damping constant with the insertion of graphene interlayer, which causes the spin mixing conductance and inverse spin Hall voltage to be significantly reduced. The observed decrease in damping constant and spin injection is attributed to the presence of magnetic proximity effect and interfacial spin-orbit scattering, which causes graphene to serve as a spin-sink layer.

Magnetic impurities as the origin of the variability in spin relaxation rates in Cu-based spin transport devices

The Elliott-Yafet spin relaxation mechanism posits linear proportionality between spin and momentum lifetimes in low spin-orbit coupling nonmagnetic metals, and is widely accepted in spintronics. Accurate experimental determination of the Elliott-Yafet proportionality constants (${\ensuremath{\beta}}_{i}$) between the spin and momentum relaxation times for individual scattering sources is challenging, however. This is apparent from the literature on nonlocal spin transport in Cu, for example, where reported phonon (${\ensuremath{\beta}}_{\mathrm{ph}}$) and defect (${\ensuremath{\beta}}_{\mathrm{def}\phantom{\rule{4pt}{0ex}}}$) Elliott-Yafet constants vary by an order of magnitude. In recent work we discovered that even part-per-million-level magnetic impurity concentrations can substantially influence spin relaxation in Cu, via a spin transport analog of the Kondo effect. To clarify whether this could explain the reported variability in ${\ensuremath{\beta}}_{i}$, here we report on a comprehensive study of spin transport in Cu-based lateral nonlocal spin valves, varying the ferromagnetic contact material, interface structure, Cu thickness, and post-fabrication annealing conditions, resulting in widely varied microstructures and magnetic impurity concentrations. Quantifying the effects of magnetic impurities on charge and spin transport we demonstrate the dramatic, even dominant, effect these can have on spin relaxation rates, and thus extracted ${\ensuremath{\beta}}_{i}$. Minimization of magnetic impurity effects is achieved via Al interlayer insertion or moderate annealing, restoring the expected temperature dependence for phonon-mediated spin relaxation, and enabling more reliable determination of ${\ensuremath{\beta}}_{i}$ for phonons (740 \ifmmode\pm\else\textpm\fi{} 200), and nonmagnetic defects (240 \ifmmode\pm\else\textpm\fi{} 50). The latter contribution is shown to be dominated by grain boundaries in these polycrystalline Cu films. Cross-sectional transmission electron microscopy measurement of grain sizes in actual nonlocal spin valve devices then establishes a useful empirical relationship between average grain size and spin diffusion length. These measurements highlight the importance of magnetic impurities in metallic spin transport, explain the wide variability in reported ${\ensuremath{\beta}}_{\mathrm{ph}}$ and ${\ensuremath{\beta}}_{\mathrm{def}}$ in Cu, and elucidate the relationship between metallic spin transport and microstructure.

Extended “Adsorption–Insertion” Model: A New Insight into the Sodium Storage Mechanism of Hard Carbons

AbstractHard carbons (HCs) are promising anodes of sodium‐ion batteries (SIBs) due to their high capacity, abundance, and low cost. However, the sodium storage mechanism of HCs remains unclear with no consensus in the literature. Here, based on the correlation between the microstructure and Na storage behavior of HCs synthesized over a wide pyrolysis temperature range of 600–2500 °C, an extended “adsorption–insertion” sodium storage mechanism is proposed. The microstructure of HCs can be divided into three types with different sodium storage mechanisms. The highly disordered carbon, with d002 (above 0.40 nm) large enough for sodium ions to freely transfer in, has a “pseudo‐adsorption” sodium storage mechanism, contributing to sloping capacity above 0.1 V, together with other conventional “defects” (pores, edges, heteroatoms, etc.). The pseudo‐graphitic carbon (d‐spacing in 0.36–0.40 nm) contributes to the low‐potential (&lt;0.1 V) plateau capacity through “interlayer insertion” mechanism, with a theoretical capacity of 279 mAh g−1 for NaC8 formation. The graphite‐like carbon with d002 below 0.36 nm is inaccessible for sodium ion insertion. The extended “adsorption–insertion” model can accurately explain the dependence of the sodium storage behavior of HCs with different microstructures on the pyrolysis temperature and provides new insight into the design of HC anodes for SIBs.

Effect of TiO2 interlayer on the performance of inverted polymeric solar cells

We report inverted bulk heterojunction organic solar cells (OSCs) by incorporating TiO2 as electron extracting layer. TiO2 was synthesized via sol-gel method. Solar cell’s active layers (P3HT/PCBM blend) were deposited using low and high spin casting of 1000 rpm (20 s) and 2000 rpm (60 s) respectively. The film deposited with 1000 rpm was kept overnight to observe solvent soaking effect. The performance parameters of the devices were enhanced with inserting TiO2 interlayer. Solvent soaked OSCs have shown enhanced device performance parameters and exhibit higher power conversion efficiency of 3.32% in comparison to reference devices. Light soaking effect of solvent soaked OSCs was also observed. The power conversion efficiency is optimized by device irradiation which activates the device by filling the trap states present in the TiO2 interface and hence improving series resistance of the OSCs. TiO2 based organic solar cells (OSC) exhibits higher performance when compared to direct structure and ZnO based inverted devices. This suggests that interfacial electron transfer rates, charge carriers combination rates and photo reactivity changed efficiently due to insertion of TiO2 interlayer between transparent electrode and device’s active layer.

Electronic structure of Ba(OH)2 interface in inverted organic photovoltaics: Improved electron transport by charged state of C60

Lowering the work function (WF) of the cathode in inverted organic photovoltaics (OPVs) is critically important to obtaining a high power conversion efficiency (PCE). The insertion of functional interlayers between the cathode and acceptor is a widely employed strategy to lower the WF. Among these functional materials, Ba(OH)2 is known to be an efficient solution-processable cathode buffer layer that improves the electron transport in organic optoelectronic devices. Despite several reports of device performance enhancement with the use of a Ba(OH)2 layer, its interfacial energetics is yet to be clearly understood. In this study, we investigated the electronic structure of Ba(OH)2 interfaces and the improvement in the PCE of inverted small molecule OPVs with the use of a Ba(OH)2 layer. On implementing the optimum thickness of the Ba(OH)2 layer, the PCE of the OPVs was significantly enhanced from 1.29% to 3.41%, and the S-shaped kink in the current-density–voltage curve was eliminated. To elucidate the underlying mechanism of this phenomenon, we explored the interfacial electronic structures of C60/indium tin oxide (ITO) and C60/Ba(OH)2/ITO using in situ photoelectron spectroscopy. The spin-coated Ba(OH)2 was physisorbed onto the ITO, which significantly reduced its WF. Owing to the Ba(OH)2, the reduced WF of the ITO is lower than the electron affinity of C60. Thus, a charge transfer is induced from Ba(OH)2/ITO to C60, and the charged states of C60 are observed within the monolayer. These charged states result in significant band bending in the C60 layer, such that its lowest unoccupied molecular orbital (LUMO) level shifts toward the Fermi level (EF) of the Ba(OH)2/ITO. As a result, the energy offset between the C60 LUMO level and the cathode EF is substantially reduced from 0.45 eV to 0.15 eV with the use of the Ba(OH)2 layer. This is the origin of the enhanced device performance of OPVs.

Effect of strain relaxation layer insertion on carrier recombination and escaping processes in superlattice solar cell structures using photoluminescence spectroscopy

We discuss the effect of interlayer insertion into the light absorption region of a carrier escape process for superlattice (SL) solar cells determined by the temperature dependence of photoluminescence (PL) signals. 20-period SL solar cells, with and without interlayers, were prepared. The temperature dependence of the integrated PL intensities due to the transition between quantum levels is well explained by the carrier relaxation models consisting of four processes: radiative and nonradiative recombinations in the SL, thermionic emission to the barrier, and tunnelling after thermal excitation from the lower to the upper levels. We observed that the activation energy for the carrier thermal escaping the quantum well was significantly reduced by the insertion of an interlayer. Moreover, the carrier thermal escaping was also found to be dominant in all processes at 300 K from the calculation of the relevant lifetimes. These results indicate that the insertion of an interlayer results in SL solar cells with a higher efficiency than conventional solar cells.