Steve Johnston
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View article: Impact of Arsenic- and Indium-Terminated InGaAs Stressors on Carrier Confinement, Strain, Defects, and Transport Properties of Tensile-Strained Ge
Impact of Arsenic- and Indium-Terminated InGaAs Stressors on Carrier Confinement, Strain, Defects, and Transport Properties of Tensile-Strained Ge Open
Device-quality tensile-strained Ge (ε-Ge) grown on a large bandgap semiconductor with superior electrical and optical carrier confinement is essential for group-IV-based optoelectronics. Properties of ε-Ge active layers synthesized on In
View article: UV + Damp Heat Induced Power Losses in Fielded Utility N‐Type Si PV Modules
UV + Damp Heat Induced Power Losses in Fielded Utility N‐Type Si PV Modules Open
A recent trend in commercial PV modules is a transition to n‐type silicon cells, including passivated emitter rear totally diffused (n‐PERT), tunnel oxide passivated contact (TOPCon), and silicon heterojunction (SHJ). There is evidence via…
View article: Sunny.jl: A Julia Package for Spin Dynamics
Sunny.jl: A Julia Package for Spin Dynamics Open
Sunny is a Julia package designed to serve the needs of the quantum magnetism community. It supports the specification of a very broad class of spin models and a diverse suite of numerical solvers. These include powerful methods for simula…
View article: Heavy boron doping effects on biaxially tensile strained germanium (>1.5%) investigated <i>via</i> structural characterization, effective lifetime assessment and atomistic modeling
Heavy boron doping effects on biaxially tensile strained germanium (>1.5%) investigated <i>via</i> structural characterization, effective lifetime assessment and atomistic modeling Open
(a) HR-TEM of 1.68% ε-Ge with boron doping of ∼7 × 1019cm −3 , (b) IFFT of ROI shows dissociation of perfect dislocation into leading 90° and trailing 30° SPDs, (c) ε-PCD lifetime improvement Het A vs. Het C, and degradation in Het B vs. H…
View article: GaAs Solar Cells Grown Directly on V-Groove Si Substrates
GaAs Solar Cells Grown Directly on V-Groove Si Substrates Open
The direct epitaxial growth of high-quality III-V semiconductors on Si is a challenging materials science problem with a number of applications in optoelectronic devices, such as solar cells and on-chip lasers. We report the reduction of d…
View article: Evaluating Performance and Degradation of Bifacial Fields: Approach and Case Study
Evaluating Performance and Degradation of Bifacial Fields: Approach and Case Study Open
This presentation cover results of four years of bifacial technology performance and degradation study, presented at the bifiPV 2024.
View article: Evaluating the Performance and Reliability of Screen-Printable Fire-Through Copper Paste on PERC Solar Cells
Evaluating the Performance and Reliability of Screen-Printable Fire-Through Copper Paste on PERC Solar Cells Open
A bifacial silicon heterojunction solar cell demands approximately 210 mg usage of silver paste (9 busbars, 24.5%, bifacial, M6 size wafer). Copper is an excellent alternative to silver: 100x cheaper, similar elecvtrical resistivities, and…
View article: R&D to Ensure a Scientific Basis for Qualification Tests and Standards (Final Report)
R&D to Ensure a Scientific Basis for Qualification Tests and Standards (Final Report) Open
Project return on investment in a photovoltaic (PV) system depends increasingly on maintaining high energy yields, and the system lifetime is a major factor in levelized cost of electricity (LCOE). Thus, the rate of PV deployment and the s…
View article: Development and Reliability of Screen-Printable Fire-Through Cu Paste for Passivated Contact Solar Cells
Development and Reliability of Screen-Printable Fire-Through Cu Paste for Passivated Contact Solar Cells Open
We present the development of copper (Cu) paste which has been screen printed on Selective Emitter-Passivated Emitter Rear Contact (SE-PERC) solar cells. This paste can also be applied to Tunnel Oxide Passivated Contact (TOPCON) solar cell…
View article: Elucidating the Role of InGaAs and InAlAs Buffers on Carrier Dynamics of Tensile-Strained Ge Double Heterostructures
Elucidating the Role of InGaAs and InAlAs Buffers on Carrier Dynamics of Tensile-Strained Ge Double Heterostructures Open
Extensive research efforts of strained germanium (Ge) are currently underway due to its unique properties, namely, (i) possibility of band gap and strain engineering to achieve a direct band gap, thus exhibiting superior radiative properti…
View article: Investigation of Sub‐Bandgap Emission and Unexpected n‐Type Behavior in Undoped Polycrystalline CdSe<sub>x</sub>Te<sub>1‐x</sub>
Investigation of Sub‐Bandgap Emission and Unexpected n‐Type Behavior in Undoped Polycrystalline CdSe<sub>x</sub>Te<sub>1‐x</sub> Open
Se alloying has enabled significantly higher carrier lifetimes and photocurrents in CdTe solar cells, but these benefits can be highly dependent on CdSe x Te 1‐x processing. This work evaluates the optoelectronic, chemical, and electronic …
View article: Crystalline Si Surface Passivation with Nafion for Bulk Defects Detection with Electron Paramagnetic Resonance
Crystalline Si Surface Passivation with Nafion for Bulk Defects Detection with Electron Paramagnetic Resonance Open
In monocrystalline Si (c-Si) solar cells, identification and mitigation of bulk defects are crucial to achieving a high photoconversion efficiency. To spectroscopically detect defects in the c-Si bulk, it is desirable to passivate the surf…
View article: Bifacial Photovoltaic Module Degradation Dynamics
Bifacial Photovoltaic Module Degradation Dynamics Open
In a comprehensive study conducted at NREL's 75 kW bifacial single-axis-tracked field, accelerated degradation was observed in four out of five bifacial silicon photovoltaic (PV) module technologies when compared to their monofacial counte…
View article: Investigation of Local Parameters of PERC Solar Cells Metallized with Screen Printed Cu-Paste
Investigation of Local Parameters of PERC Solar Cells Metallized with Screen Printed Cu-Paste Open
For 40 TW of PV required to transition our planet to 100% renewables, the silver (Ag) should disappear from PV production. Advantages of copper (Cu) over silver (Ag) include: 1) bulk Cu has a similar conductivity to Ag (1.7 one millionth O…
View article: BEST Field Degradation Research
BEST Field Degradation Research Open
Data for control and 5-year fielded bifacial modules of PERC and SHJ technologies, including IV Curves, EQE, EL and PL, for degradation and performance studies.
View article: GeSn-on-GaAs with photoconductive carrier lifetime >400 ns: role of substrate orientation and atomistic simulation
GeSn-on-GaAs with photoconductive carrier lifetime >400 ns: role of substrate orientation and atomistic simulation Open
Microwave reflection photoconductive decay carrier lifetimes of Ge0.94Sn0.06 materials on oriented GaAs substrates at 300 K.
View article: Monolithically Integrated <i>ϵ</i>-Ge/In<sub>x</sub>Ga<sub>1-x</sub>As Quantum Well Laser Design: Experimental and Theoretical Investigation
Monolithically Integrated <i>ϵ</i>-Ge/In<sub>x</sub>Ga<sub>1-x</sub>As Quantum Well Laser Design: Experimental and Theoretical Investigation Open
Here, we have analyzed the electrical and optical phenomenon occurring in a $\\varepsilon$-Ge/In x Ga 1-x -Ge/In x Ga 1-x As quantum well (QW) laser through self-consistent physical solvers calib…
View article: Degradation-related defect level in weathered silicon heterojunction modules characterized by deep level transient spectroscopy
Degradation-related defect level in weathered silicon heterojunction modules characterized by deep level transient spectroscopy Open
View article: Optoelectronic and structural characterization of trapezoidal defects in 4H-SiC epilayers and the effect on MOSFET reliability
Optoelectronic and structural characterization of trapezoidal defects in 4H-SiC epilayers and the effect on MOSFET reliability Open
To this day, trapezoidal defects are found in clusters and high counts in wafers representing the industry standard in terms of material quality being produced. This study sheds light on the nature, origin, behavior, and impact of this def…
View article: Solar Energy from a Big Picture Perspective to Nanoscale Insights via TOF-SIMS
Solar Energy from a Big Picture Perspective to Nanoscale Insights via TOF-SIMS Open
The world is undergoing a rapid transformation in the ways that we generate and store energy. This has been driven not only by concerns about the climate but by simple economic factors due to the dramatic cost decreases in wind in solar po…
View article: GaAs solar cells grown on acoustically spalled GaAs substrates with 27% efficiency
GaAs solar cells grown on acoustically spalled GaAs substrates with 27% efficiency Open
View article: Stacking Faults Originating from Star-Defects in 4H-SiC
Stacking Faults Originating from Star-Defects in 4H-SiC Open
Intense efforts are currently in progress to study various sources of basal plane dislocations (BPDs) in SiC epitaxial layers. BPDs can generate Shockley-type stacking faults (SSFs) in SiC epitaxial layers, which have been shown to be asso…
View article: The effect of dopant concentration and annealing treatments on N-type Iodine doped CdTe
The effect of dopant concentration and annealing treatments on N-type Iodine doped CdTe Open
View article: Analysis of Crystalline Defects Caused by Growth on Partially Planarized Spalled (100) GaAs Substrates
Analysis of Crystalline Defects Caused by Growth on Partially Planarized Spalled (100) GaAs Substrates Open
We analyze the effect of growth on non-(100) surfaces resulting from incomplete planarization of spalled GaAs wafers on the defect structure of GaAs solar cell layers grown by hydride vapor phase epitaxy (HVPE). Controlled spalling of (100…
View article: Apparatus and method for measuring minority carrier lifetimes in semiconductor materials
Apparatus and method for measuring minority carrier lifetimes in semiconductor materials Open
An apparatus for determining the minority carrier lifetime of a semiconductor sample includes a positioner for moving the sample relative to a coil. The coil is connected to a bridge circuit such that the impedance of one arm of the bridge…
View article: Radio frequency coupling apparatus and method for measuring minority carrier lifetimes in semiconductor materials
Radio frequency coupling apparatus and method for measuring minority carrier lifetimes in semiconductor materials Open
An apparatus for measuring the minority carrier lifetime of a semiconductor sample using radio-frequency coupling. The measuring apparatus includes an antenna that is positioned a coupling distance from a semiconductor sample which is expo…
View article: Compositional texture engineering for highly stable wide-bandgap perovskite solar cells
Compositional texture engineering for highly stable wide-bandgap perovskite solar cells Open
The development of highly stable and efficient wide-bandgap (WBG) perovskite solar cells (PSCs) based on bromine-iodine (Br–I) mixed-halide perovskite (with Br greater than 20%) is critical to create tandem solar cells. However, issues wit…
View article: Correspondence: Bill of Materials Variation and Module Degradation in Utility-Scale PV Systems
Correspondence: Bill of Materials Variation and Module Degradation in Utility-Scale PV Systems Open
We report photovoltaic (PV) modules of the same make and model are often assembled with different bills of materials (BOMs). In this correspondence, we revisit two case studies of utility-scale silicon PV systems in which these differing B…
View article: Nanometer-Scale Measurement of Grid Finger Electrical Conduction Pathways to Detect Series Resistance Degradation of Utility-Scale Silicon Solar Cells
Nanometer-Scale Measurement of Grid Finger Electrical Conduction Pathways to Detect Series Resistance Degradation of Utility-Scale Silicon Solar Cells Open
Here, we report on an electrical conduction mechanism for series resistance (Rs) degradation observed in a utility-scale photovoltaic power plant by imaging the local resistance at the Ag/Si interface of the c-Si front metallization. Scann…
View article: A performance comparison between GaInP-on-Si and GaAs-on-Si 3-terminal tandem solar cells
A performance comparison between GaInP-on-Si and GaAs-on-Si 3-terminal tandem solar cells Open