Parasitic Losses Research Articles

(Invited) The Promise and Challenges of Using Selective Ion Insertion Electrodes for Water Deionization

Electrochemical de-ionization methods show great promise in complementing existing membrane based desalination technologies in purifying water over a range of salinity values.1 These methods have shown superior energy requirements and efficiency in de-ionizing low salinity waters.2 Further, many water treatment processes require removal of a small number of ionic impurities; for example arsenic in drinking water, nitrates and phosphates in wastewater as well as sodium in agricultural feed water. In this work, we demonstrate the feasibility of using insertion materials as electrodes in electrochemical de-ionization systems. Insertion compounds are inorganic polyionic crystalline materials that upon exposure a specific redox potential will undergo a change in transition state of the host transition metal species. In doing so, the compound accepts within its host structure, ions that meet the size limitations imposed by its crystal structure and the charge required to maintain electroneutrality. As such, these materials are more selective with regard to the specific ions that are sorbed when compared with porous carbon .electrodes. Additionally, these materials show nearly an order of magnitude higher ion removal capacity than traditional electric double layer carbon materials (less than 0.2 mmol/g) as well as high round trip coulombic efficiencies.3-5 We probe sodium-ion selective materials specifically a NASICON type phase change material, NaTi2(PO4)3 and a layered insertion material Na4Mn9O18 with respect to their sodium ion removal capabilities over a range of inserting ion concentrations as well as over a range of concentrations of non-inserting cations. We demonstrate that in dilute solutions of inserting ions, we encounter higher concentration overpotentials, bulk transport limitations and parasitic charge losses that reduce the coulombic efficiency of the insertion electrodes. Our results also show that at any given concentration of electrolyte, there is a critical current at we balance interfacial ion transport to the migration of ions from bulk to the electrode surface. At this current, we have are fully able to utilize the electrode capacity while minimizing parasitic charge loss. A similar reduction in coulombic efficiency and ion removal capacity is observed when the concentration of non-inserting cations is increased. This can be attributed to due to competing transport of the non-inserting cations to the electrode surface and reduction in the limiting current in presence of non-inserting ions. Additionally, a penalty in round trip coulombic efficiency is encountered when non-inserting ions are present. As such, the use of insertion compounds could be limited to use in water streams where the inserting ion is the dominant species. To overcome this, we propose alternatives such as improving advective transport and proper selection of operating current densities to overcome some of the above-mentioned challenges and achieve improved separation of the inserting ions, in this case sodium ions from dilute and multi-ionic water streams.

(Invited) Direct Formic Acid Fuel Cells Anode Optimization: Flow Fields and Catalysts

Direct formic acid fuel cells (DFAFCs) offer an efficient and compact electrochemical conversion technology to power portable electronic devices ranging from sensors to unmanned surveillance vehicles. Liquid fuel cells are desirable for portable applications due to their ease of liquid refueling and the minimal incorporation of system fail safes for handling, as compared to compressed gasses. Directly compared to other liquid fuels, formic acid has minimal parasitic losses due to (i) efficient anodic overpotentials and (ii) cathodic depolarization due to low fuel crossover.[1]The anodic overpotentials are reduced in the presence of efficient catalysts that enhance the fraction of formic acid that is electro-oxidized via the direct non-strongly adsorbed reaction intermediate pathway,[2] while most liquid fuels are plagued with strongly adsorbed carbon monoxide reaction intermediates that require high parasitic overpotentials. Fig 1 compares the formic acid overpotential on a platinum-ruthenium (PtRu) alloy catalyst through the indirect electro-oxidation pathway and carbon supported platinum catalyst decorated with a submonolayer of bismuth (Pt/C-Bi) promoting the direct electro-oxidation pathway. Two short comings incurred in a DFAFC are (Part 1) durability of the catalyst and (Part 2) efficient removal of the CO2-byproduct.[3] Part 1 – The Bi, at 54% of a monolayer coverage, promotes the direct electro-oxidation pathway by the ‘third-body’ effect and adsorption in the CH-down orientation. Alternative adsorbates to Bi are being sought that are strongly adsorbed to the Pt surface and enhance formic acid electro-oxidation through the direct reaction pathway. Stability of the adsorbate during operation and idle will be a key parameter in down selection. Part 2 – The removal of CO2 is imperative to maintain elevated formic acid concentration both in the anode flow field and at the catalyst interfaces within the 3-dimensional anode catalyst layer. The limited crossover of formic acid to the cathode permits the cell to be operated in the presences of neat fuel concentrations. Previously in the Rice group, it has been shown that DFAFC performance is strongly impacted by catalyst layer porosity via either swelling of the catalyst layer[4] or using a pore former to create larger pore structures in the catalyst layer[5]. As the DFAFC operates under higher loads, additional CO2 must be removed through a typical single serpentine flow field, resulting in non-uniformed fuel distribution at the catalyst interface due to two-phase flow. Recent work on advanced electrically conductive selectively gas permeable anode flow field (SGPFF) designs have resulted in efficient removal of CO2 perpendicular to the active area near the location where it is formed in the catalyst layer.[6] Fig 2 shows the potentiostatic hold performance (0.3V) in a dead-ended flow field operation for a standard flow field vs. the SGPFF using PtRu/C as the anode catalyst. Acknowledgements: We gratefully acknowledge support of this work by the NSF-funded TN-SCORE program, NSF EPS-1004083, under Thrust 2 and the Center for Manufacturing Research at Tennessee Tech University.

Modeling the Performance Limitations and Prospects of Perovskite/Si Tandem Solar Cells under Realistic Operating Conditions.

Perovskite/Si tandem solar cells have the potential to considerably out-perform conventional solar cells. Under standard test conditions, perovskite/Si tandem solar cells already outperform the Si single junction. Under realistic conditions, however, as we show, tandem solar cells made from current record cells are hardly more efficient than the Si cell alone. We model the performance of realistic perovskite/Si tandem solar cells under real-world climate conditions, by incorporating parasitic cell resistances, nonradiative recombination, and optical losses into the detailed-balance limit. We show quantitatively that when optimizing these parameters in the perovskite top cell, perovskite/Si tandem solar cells could reach efficiencies above 38% under realistic conditions, even while leaving the Si cell untouched. Despite the rapid efficiency increase of perovskite solar cells, our results emphasize the need for further material development, careful device design, and light management strategies, all necessary for highly efficient perovskite/Si tandem solar cells.

Fischer-Tropsch Synthesis in supercritical Co2 – Inhibition of Co2 selectivity for enhanced hydrocarbon production

It has been generally observed that the fraction of the carbon in coal reporting as non methane hydrocarbons during coal to liquid (CTL) fuels process employing gasification and Fischer Tropsch Synthesis (FTS) using Fe based catalysts is less than 17% while theoretical limit for a CTL is around 52%. The use of supercritical CO2 as a solvent for FTS is shown to increase the reaction rates, suppress CO2 selectivity, reduce CH4 selectivity and thereby increase chain growth and improve the heat transfer and wax dissolution characteristics to increase catalyst longevity. This paper presents the results from proof of concept studies on FT synthesis in supercritical CO2 from syngas (H2:CO ∼1:1) typically produced from coal gasification and using a Fe-Zn-K/γ-alumina catalyst. Experiments were conducted with syngas alone, syngas diluted with N2 and syngas diluted with CO2. The high pressures improved the conversions and reduced the CO2 emissions. The dilution with N2 somewhat improved the CO conversions and CO2 emissions. However, CH4 emissions were found to increase. When diluted with CO2 and experiments conducted at pressures above the critical pressure, the data show, both, an overall shift in the product distribution towards higher hydrocarbons and reduction in the parasitic loss of carbon efficiency due to carbon dioxide formation along with significant improvement in the conversion rates. The use of the supercritical CO2 (ScCO2) inhibited methane and converted some of the CO2.

Parasite community dynamics in an invasive vole – From focal introduction to wave front

Multiple parasite species simultaneously infecting a host can interact with one another, which has the potential to influence host-parasite interactions. Invasive species typically lose members of their parasite community during the invasion process. Not only do the founding population escape their parasites, but the rapid range expansion of invaders once in the invaded range can lead to additional stochastic loss of parasites. As such, parasite community dynamics may change along an invasion gradient, with consequences for host invasion success. Here, we use the bank vole, Myodes glareolus, introduced as a small founding population at a point source in the Republic of Ireland in c.1920's and its ecto- and endoparasites to ask: i) how does the parasite community vary across an invasion gradient, and ii) are parasite community associations driven by host traits and/or distance from the point of host introduction? We sampled the parasite community of M. glareolus at the proposed focal site of introduction, at mid-wave and the invasion front, and used a parasite interactivity index and statistical models to determine the potential for the parasite community to interact. Bank voles harboured up to six different parasite taxa, with a significantly higher parasite interactivity index at the foci of introduction (z = 2.33, p = 0.02) than elsewhere, suggesting the most established parasite community has greater opportunities to interact. All but one of four synergistic parasite community associations were driven by host traits; sex and body mass. The remaining parasite-parasite associations occurred at the mid-point of the invasion wave, suggesting that specific parasite-parasite interactions are not mediated by distance from a focal point of host introduction. We propose that host traits rather than location along an invasion gradient are more likely to determine parasite-parasite interactions in the invasive bank vole.

CFD study of leakage flows in shroud cavities of a compressor impeller

The flow character in a gap between shroud disc of an impeller and a stator surface (shroud cavity) influences disc friction loss, labyrinth seal loss (parasitic losses) and thrust force. Flow calculations inside the shroud cavity of a model of centrifugal compressor stage and its labyrinth seal in a range of flow rates and axial width and radial gap are presented. The results are presented in terms of non-dimensional coefficients of flow, disc friction and seal leakage losses coefficients and pressure coefficient. The distributions meridional and tangential flow velocities correspond to the continuity and equilibrium equations – flow radial circulation exists in wide cavity and is absent in narrow cavities. The radial pressure distributions as measured and calculated are not fully comparable. The possible reason is that CFD-calculated leakage coefficient is less than calculated by A.Stodola formula. The influence of a cavity width on the losses and the thrust force requires a balanced design.

Switched Substrate-Shield-Based Low-Loss CMOS Inductors for Wide Tuning Range VCOs

A switched substrate-shield inductor (SSI) topology in bulk CMOS is proposed which minimizes parasitic capacitance and substrate losses, while tuned magnetically induced currents facilitate inductor tunability. The high frequency behavior of the induced current is analyzed, resulting in intuitive insights and design guidelines for a high-performance SSI. An SSI prototype in 65-nm bulk CMOS achieves 34% inductance tunability with a quality factor of >10.3. A voltage-controlled oscillator (VCO) using SSI achieves 40.3% tuning range, from 21 to 31.6 GHz, and a phase noise of −119.1 ± 3.7 dBc/Hz at 10-MHz offset frequencies. The VCO core consumes 4.3 ± 0.2 mW from a 1-V supply.

Improved performance of open volumetric receivers by employing an external air return system

In solar central receiver power plants open volumetric receivers using air as heat transfer fluid are an alternative to the currently predominant receiver types, namely salt and steam receivers. In order to improve their competitiveness, the receiver performance has to be improved. In the current study an external air return system has been integrated in the Solar Tower Julich and its influence on power plant performance has been investigated. With this system, the parasitic losses caused by the fans are reduced by up to 34%. The measured air return ratio is mostly unaffected, but the current data suggest, that the internal and external convective losses of the receiver are reduced when an external air return system is applied. A positive influence of the total mass flow on the air return ratio has been identified for the current data while other parameters like the return air temperature turned out to be less significant.

Perovskite Nanopillar Array Based Tandem Solar Cell

One of the promising approaches to improve the efficiency of conventional single-crystalline silicon (c-Si) solar cells is their integration in a tandem arrangement. In this perspective, inorganic–organic perovskites are an ideal blend of materials to combine with c-Si owing to their complementary light absorption characteristics. Even though interesting and promising combinations of perovskite/c-Si-based solar cells have been presented, their overall efficiency has been limited by the photocurrent reduction occurring in both perovskite and silicon due mostly to reflection and parasitic losses. Here, we envision and model a new design strategy for an efficient light-to-current conversion through the use of a nanopillar array based perovskite/c-Si tandem solar cell. The optical–electrical performance of the proposed architecture is analyzed by a 3D finite-element numerical model. In particular, we have searched for the best optical enhancement conditions through the tuning of the cell geometrical parameter...

In-situ terahertz optical Hall effect measurements of ambient effects on free charge carrier properties of epitaxial graphene

Unraveling the doping-related charge carrier scattering mechanisms in two-dimensional materials such as graphene is vital for limiting parasitic electrical conductivity losses in future electronic applications. While electric field doping is well understood, assessment of mobility and density as a function of chemical doping remained a challenge thus far. In this work, we investigate the effects of cyclically exposing epitaxial graphene to controlled inert gases and ambient humidity conditions, while measuring the Lorentz force-induced birefringence in graphene at Terahertz frequencies in magnetic fields. This technique, previously identified as the optical analogue of the electrical Hall effect, permits here measurement of charge carrier type, density, and mobility in epitaxial graphene on silicon-face silicon carbide. We observe a distinct, nearly linear relationship between mobility and electron charge density, similar to field-effect induced changes measured in electrical Hall bar devices previously. The observed doping process is completely reversible and independent of the type of inert gas exposure.

Influence of Operating Parameters and System Design on Efficiency of Biomass and Biogas Based SOFC Systems

With the recent COP 21 declaration many countries have dedicated themselves to a clear path towards decarbonization. This requires major installation of wind and solar power. However, these only provide intermittent electricity. Thus, balance power has to be provided, ideally from renewable resources. Currently only biomass seems to be available in large enough quantity to provide significant balancing power. A wide range of biomass feedstocks can be made available for power generation for example via anaerobic digestion or thermo-chemical gasification. However, resources are still limited. Hence, in order to maximize its potential the biomass has to be used at the highest possible efficiency. Electrochemical conversion, especially in SOFC, in general offers very high efficiency. However, also in SOFC systems the choice of the optimal system design and operating parameters can make a big difference. The presented work investigates utilization of biogas and syngas from biomass gasification in different system designs. This is done using a thermodynamic SOFC model built in Aspen Plus, which has been validated against literature data. A comparison to cell and stack performance of the well known manufacturers Fuel Cell Energy and Forschungszentrum Jülich is presented. It is shown that at identical operating conditions the model shows slightly worse performance than the real stacks. With the model, the influence of different fuel pre-treatment and pre-reforming options are compared at a fixed stack size. Furthermore the effect of anode offgas recirculation, as well as the choice of fuel utilization, oxidant, operating temperature and pressure are investigated. During the analysis operating conditions prone to the risk of carbon deposition are excluded. Also the impact on the balance of plant is taken into account. Results show, that depending on the fuel, system design and parameters the electrical efficiency of the fuel cell alone can vary between 35 and 71%. From this, depending on the system parasitic consumption and losses of up to 8% points have to be subtracted. Thus, net AC efficiencies reach 30 to 63%. Finally a new system design and operating regime is proposed, which can significantly raise the DC efficiency while reducing the parasitic consumption by adjusting the gas treatment and operating parameters. Modelling results of new design show net AC system efficiencies of up to 72%.

Improving Operation of a 2.5kW SOFC Power System with Supervisory Control

Operation of the SOFC power system can be improved by upgrading the low-level controllers with a supervisory controller (see Figure 1). In this work a simple, model-free supervisory optimizer that adjusts references for the low level controllers is proposed. The optimization problem for the SOFC power system is formulated with the cost function depending on the electrical efficiency of the system and deviations of the system temperatures from their limits. Electrical efficiency is calculated as the ratio of the net electrical power to the total power obtained by burning the fuel. The dominant parasitic losses of the system are assumed to be mainly related to the air blower consumption. Based on efficiency analysis, which demands a number of simulations on SOFC power system model, the references for the burner lambda and stack outlet and inlet air temperatures are selected as optimization variables. The optimization problem is solved by using the extremum-seeking approach where optimum is sought directly on the process. An advantage of this approach is that it does not need a model of the system and exceeds the weakness of model-based optimizers, which assume nominal process condition all the time and do not take into account the degradation processes in fuel cells. Its disadvantage is it needs to probe the system at all time by imposing small variations on manipulated variables and delivers a convergence speed which is somewhat slower compared to the model based approach. A simple algorithm is designed to perform the model-free optimization. The algorithm is additionally augmented to incorporate changes in the current load in order to increase the convergence speed of the optimization at large load changes. The efficiency of the optimizer is governed by properly tuned parameters of the optimization algorithm. Proposed supervisory optimizer is assessed on a simulated detailed physical model of a 2.5 kW SOFC power system by applying large step current load changes. Simulation results indicate that the optimizer improves efficiency of the system by approximately 10 % compared to the low-level controllers and keeps the system temperatures within the safe ranges (see Figure 2). Due to its simplicity the optimizer appears appropriate for practical applications. Figure 1

Effects of micro-milled malposed dimple structures on tribological behavior of Al-Si alloy under droplet lubricant condition

To solve the problem of undesired rapid wear of the piston and high leakage in the combustion chamber, various technical approaches have been presented to decrease the friction between internal compression piston ring and cylinder liner. Surface micro-texturing is one of the most efficient methods to mitigate parasitic losses. In this paper, surface micro-textures with different dimple distribution angles (15°, 45°, 60°, and 90°) were fabricated by micro-milling on Al-Si alloy ZL109. Pin-on-disc reciprocating tribometer was utilized to investigate the effects of the malposed rectangle dimple structures on the tribological behaviors of ZL109. The friction coefficient and wear topographies of the textured specimens with different distribution angles were examined. The possible friction reduction and wear resistant mechanisms were analyzed. The results indicated that the friction performance of machined surface could be enhanced by the malposed rectangle dimple micro-textures. The average friction coefficient of dimple distribution angle θ = 45° reduced by 6.93% in comparison to the untextured specimens. Furthermore, optical micrographs indicated that the micro-textured specimens with distribution angle θ of 60° exhibited the narrowest and shallowest wear track.

Flexible thermoelectric generator using bulk legs and liquid metal interconnects for wearable electronics

Interest in wearable electronics for continuous, long-term health and performance monitoring is rapidly increasing. The reduction in power levels consumed by sensors and electronic circuits accompanied by the advances in energy harvesting methods allows for the realization of self-powered monitoring systems that do not have to rely on batteries. For wearable electronics, thermoelectric generators (TEGs) offer the unique ability to continuously convert body heat into usable energy. For body harvesting, it is preferable to have TEGs that are thin, soft and flexible. Unfortunately, the performances of flexible modules reported to date have been far behind those of their rigid counterparts. This is largely due to lower efficiencies of the thermoelectric materials, electrical or thermal parasitic losses and limitations on leg dimensions posed by the synthesis techniques. In this work, we present an entirely new approach and explore the possibility of using standard bulk legs in a flexible package. Bulk thermoelectric legs cut from solid ingots are far superior to thermoelectric materials synthesized using other techniques. A key enabler of the proposed technology is the use of EGaIn liquid metal interconnects, which not only provide extremely low interconnect resistance but also stretchability with self-healing, both of which are essential for flexible TE modules. The results suggest that this novel approach can finally produce flexible TEGs that have the potential to challenge the rigid TEGs and provide a pathway for the realization of self-powered wearable electronics.

Fabrication of Superconducting Vacuum-Gap Crossovers for High Performance Microwave Applications

The design and fabrication of low-loss wide-bandwidth superconducting vacuum-gap crossovers for high performance millimeter wave applications are described. In order to reduce ohmic and parasitic losses at millimeter wavelengths a vacuum gap is preferred relative to dielectric spacer. Here, vacuum-gap crossovers were realized by using a sacrificial polymer layer followed by niobium sputter deposition optimized for coating coverage over an underlying niobium signal layer. Both coplanar waveguide and microstrip crossover topologies have been explored in detail. The resulting fabrication process is compatible with a bulk micro-machining process for realizing waveguide coupled detectors, which includes sacrificial wax bonding, and wafer backside deep reactive ion etching for creation of leg isolated silicon membrane structures. Release of the vacuum gap structures along with the wax bonded wafer after DRIE is implemented in the same process step used to complete the detector fabrication

Potentials of mixed-phase doped layers in p-type Si heterojunction solar cells with ZnO:Al

We present and discuss advances in the development of p-type Si heterojunction solar cells with Al-doped ZnO (AZO) on both front and rear side, by means of mixed-phase Si- and SiOx-based doped layers. We demonstrate that while rear AZO can be deleterious when using p-type amorphous silicon (a-Si:H), p-type microcrystalline silicon (μc-Si:H) allows for: (1) suppression of the p-layer/AZO Schottky-like barrier, (2) relevant Voc increase, and (3) improved transport and extraction of carriers. In contrast, Voc reduction and increased low-injection recombination is observed with n-type μc-Si:H in conjunction with AZO, likely due to the low defect density of the material which entails severe depletion effects. These issues are avoided with the more defective mixed-phase n-SiOx, which additionally provides for reduced parasitic absorption losses and is thus established as the optimal emitter choice.

Investigation on the Performance of CIGS/TiO2 Heterojunction Using SCAPS Software for Highly Efficient Solar Cells

In this study, Cu (In, Ga) Se2 (CIGS) material with the non-toxic titanium dioxide TiO2 as an n-type buffer layer and indium tin oxide as the window layer are numerically simulated using a solar cell capacitance simulation software package. This numerical analysis has been carried out with the aim of boosting the performances of CIGS/TiO2 solar cells by tuning the defect density and band gap energy of the ordered vacancy compound (OVC) layer and by using a Back-electron reflector (EBR) layer, namely Al2O3. Solar cell performance is investigated as a function of absorber thickness. It is found that there exists an optimal thickness. The effect of OVC compounds on the performance of the device structure are discussed leading to an optimal band gap energy and defect density of about 1.17 eV and 4.97 × 1013 cm−3, respectively. The matching solar cell conversion efficiency reached a maximum value of 12.38% by introducing the OVC layer. It is also shown that, in spite of a decrease in thickness, the external quantum efficiency (EQE) of ultrathin CIGS solar cells can be enhanced owing to the employment of EBR. The significant improvement of EQE, mainly in the near-infrared part of the solar spectrum, can be ascribed to the low parasitic absorption loss in the ultrathin CIGS layer (∼570 nm).

Efficiency of the Inertia Friction Welding Process and Its Dependence on Process Parameters

It has been widely assumed, but never proven, that the efficiency of the inertia friction welding (IFW) process is independent of process parameters and is relatively high, i.e., ~70 to 95 pct. In the present work, the effect of IFW parameters on process efficiency was established. For this purpose, a series of IFW trials was conducted for the solid-state joining of two dissimilar nickel-base superalloys (LSHR and Mar-M247) using various combinations of initial kinetic energy (i.e., the total weld energy, E o), initial flywheel angular velocity (ω o), flywheel moment of inertia (I), and axial compression force (P). The kinetics of the conversion of the welding energy to heating of the faying sample surfaces (i.e., the sample energy) vs parasitic losses to the welding machine itself were determined by measuring the friction torque on the sample surfaces (M S) and in the machine bearings (M M). It was found that the rotating parts of the welding machine can consume a significant fraction of the total energy. Specifically, the parasitic losses ranged from 28 to 80 pct of the total weld energy. The losses increased (and the corresponding IFW process efficiency decreased) as P increased (at constant I and E o), I decreased (at constant P and E o), and E o (or ω o) increased (at constant P and I). The results of this work thus provide guidelines for selecting process parameters which minimize energy losses and increase process efficiency during IFW.

RF loss mechanisms in GaN‐based high‐electron‐mobility‐transistor on silicon: Role of an inversion channel at the AlN/Si interface

One of the epitaxial issues pertaining to the growth of AlGaN/GaN HEMTs on Si is the decrease of parasitic losses that can adversely impact the RF device performances. We characterized the microwave losses in coplanar waveguides (CPWs) on GaN‐based high‐electron‐mobility‐transistors (HEMTs) and their buffer layers on Silicon substrate, up to 40 GHz. The RF losses depend not only on the crystalline quality but also on the residual tensile stress in AlN buffer, as well as its thickness. The mechanism of interfacial lossy channel induced by the piezoelectric field is discussed. Adopting a thin high‐low‐high temperature (HLH) AlN buffer can help to reduce the tensile stress leading to a reduction of RF losses. We suggest that a thinner p‐type AlN and/or p‐AlGaN‐on‐thin AlN near the interface can suppress the electron interfacial lossy channel, which helps the GaN‐HEMT‐on‐HR Si to remain in a high frequency range and at high‐temperature operation.

InAlAs photovoltaic cell design for high device efficiency

AbstractThis study presents a new design for a single‐junction InAlAs solar cell, which reduces parasitic absorption losses from the low band‐gap contact layer while maintaining a functional window layer by integrating a selective etch stop. The etch stop is then removed prior to depositing an anti‐reflective coating. The final cell had a 17.9% efficiency under 1‐sun AM1.5 with an anti‐reflective coating. Minority carrier diffusion lengths were extracted from external quantum efficiency data using physics‐based device simulation software yielding 170 nm in the n‐type emitter and 4.6 μm in the p‐type base, which is more than four times the diffusion length previously reported for a p‐type InAlAs base. This report represents significant progress towards a high‐performance InAlAs top cell for a triple‐junction design lattice‐matched to InP. Copyright © 2017 John Wiley & Sons, Ltd.