Optimization of Multijunction Solar Cells Through Indoor Energy Yield Measurements

et al. 2015

IEEE J. Photovoltaics

Self Cite

Abstract-Nonradiative recombination in inverted GalnP junctions is dramatically reduced using a rear-heterojunction design rather than the more traditional thin-emitter homojunction design. When this GalnP junction design is included in inverted multijunction solar cells, the high radiative efficiency translates into both higher subcell voltage and high luminescence coupling to underlying subcells, both of which contribute to improved performance. Subcell voltages within two and four junction devices are measured by electroluminescence and the internal radiative efficiency is quantified as a function of recombination current using optical modeling. The performance of these concentrator multijunction devices is compared with the Shockley-Queisser detailed-balance radiative limit, as well as an internal radiative limit, which considers the effects of the actual optical environment in which a perfect junction may exist.

Section: Four Junction-inverted Metamorphic Solar Cellsmentioning

confidence: 87%

Implications of Redesigned, High-Radiative-Efficiency GaInP Junctions on III-V Multijunction Concentrator Solar Cells

Geisz

Steiner

et al. 2015

IEEE J. Photovoltaics

Self Cite

“…However, the other parameters (AOD, PW, etc.) can cause also significant variations in the spectral content [1]. Although these parameters do not change as rapidly as the AM does, their seasonal variation can influence the optimum design and energy production of a multijunction solar cell.…”

Section: Binning Methodsmentioning

confidence: 99%

“…Complete annual spectra datasets for the site need to be available and used to optimize the multijunction solar cell design for maximum energy production. Moreover, the time bins in these datasets have to be small enough so as to minimize errors introduced by possible rapid atmospheric changes, such as clouds occluding temporarily the direct beam for concentrator solar cells [1]. The 1-hour time bin typically used can introduce large errors in the prediction of the energy production, and narrower time bins are necessary.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, reproducing this large quantity of spectral compositions experimentally for indoor energy production measurements using the method we presented in [1] is not practical: for 1-sun measurements, the limitation is the time-consuming measurement process; for concentration measurements, an additional constraint is the difficulty in generating many different spectral compositions in a typical flash simulator.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Field spectra binning for energy production calculations and multijunction solar cell design

2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC)

McMahon

Habte

et al. 2015

Self Cite

-Annual spectra sets must be used for accurate energy production prediction and multijunction solar cell design for maximum energy production at a specific site. These spectra sets contain a large quantity of data that is cumbersome to manage during solar cell design calculations and impractical to reproduce in solar simulators for indoor energy production measurements. However, it should be possible to bin together spectra with similar spectral contents, and then use this reduced set with little loss of accuracy. We present two binning algorithms which judiciously bin together similar spectra to create a much smaller "proxy" set, for which the total measurement time, energy production calculation and solar cell optimization decreases to a matter of seconds. These algorithms are assessed against their accuracy in representing the whole spectra sets for solar cell design and energy production prediction. We find that a set of just five spectra fulfills this requirement. In addition, the sets of proxy spectra act as "fingerprints" of specific sites, and provide an efficient and effective way to understand how cell design and performance vary from site to site. Furthermore, the process of reducing a full data set to a few proxy spectra can help assess the quality of the dataset for multijunction applications, and contribute to improvements to the datasets and data collection methods.

“…The design flexibility of the 4J-IMM allows fine-tuning the device for different operating conditions, and maximizing the yearly energy yield of the device [4][5]. To illustrate this design flexibility, we designed multijunction solar cells for the direct, global, and AMO spectra.…”

Section: Designsmentioning

confidence: 99%

Design flexibility of ultra-high efficiency 4-junction inverted metamorphic solar cells

Geisz

2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC)

Steiner

et al. 2015

Self Cite

-We present recent improvements to the 4-junction inverted metamorphic solar cell. The device now includes a (Ga)InAsP buffer that transitions to lattice constants greater than InP, which allows access to GalnAs subcells with bandgaps < 0.74 eV and an additional 2 mA/cm 2 of bottom junction photocurrent at AM1.5D. However, the optimal design depends on the spectrum and operating temperature. We show how the device flexibility can be used to fine-tune the design for various spectra in order to maximize energy yield for a given operating condition. 1-sun devices achieve 35.3% efficiency under the AMO spectrum and 37.8% efficiency under the global spectrum at 25°C. Concentrator devices achieve 45.7% peak efficiency under 234x the direct spectrum and maintain over 45% efficiency at 700x at 25°C. Other device improvements include a 4-layer antireflection coating with low power loss, and reduced series resistance.