Combined Effects of Shunt and Luminescence Coupling on External Quantum Efficiency Measurements of Multijunction Solar Cells

Li, Jingjing; Lim, S. H.; Allen, Charles R.; Ding, Ding; Zhang, Yong-Hang

doi:10.1109/jphotov.2011.2172188

Cited by 45 publications

(26 citation statements)

References 7 publications

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“…Carriers are generated by the absorption of both solar radiation, n i sun , and coupled spontaneous emission from the adjacent largerbandgap i À 1 junction, [9][10][11][12] n iÀ1 sp;lower , where N iÀ1 sp;lower…”

Section: Auger Loss Energy Lost To Auger Recombinationmentioning

confidence: 99%

“…Moreover, most commercial software packages consider both radiative and non-radiative recombination [4][5][6] however, they typically do not include some important aspects related to radiative recombination, such as photon recycling 7,8 within a given junction and spontaneous emission coupling between adjacent junctions. [9][10][11][12] On the contrary, detailed balance models are only capable of clarifying the fundamental limitations of ideal solar cells by neglecting many important mechanisms that occur in real devices. It is, therefore, necessary to develop a semi-analytical model that not only takes into account all of the important properties of materials and device structures to provide a more thorough understanding of photovoltaic solar cells, but also enables fast computation to offer basic guidance for practical device design.…”

Section: Introductionmentioning

confidence: 99%

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A semi-analytical model for semiconductor solar cells

Ding

Johnson

et al. 2011

Journal of Applied Physics

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A semi-analytical model is constructed for single- and multi-junction solar cells. This model incorporates the key performance aspects of practical devices, including nonradiative recombination, photon recycling within a given junction, spontaneous emission coupling between junctions, and non-step-like absorptance and emittance with below-bandgap tail absorption. Four typical planar structures with the combinations of a smooth/textured top surface and an absorbing/reflecting substrate (or backside surface) are investigated, through which the extracted power and four types of fundamental loss mechanisms, transmission, thermalization, spatial-relaxation, and recombination loss are analyzed for both single- and multi-junction solar cells. The below-bandgap tail absorption increases the short-circuit current but decreases the output and open-circuit voltage. Using a straightforward formulism this model provides the initial design parameters and the achievable efficiencies for both single- and multiple-junction solar cells over a wide range of material quality. The achievable efficiency limits calculated using the best reported materials and AM1.5 G one sun for GaAs and Si single-junction solar cells are, respectively, 27.4 and 21.1% for semiconductor slabs with a flat surface and a non-reflecting index-matched absorbing substrate, and 30.8 and 26.4% for semiconductor slabs with a textured surface and an ideal 100% reflecting backside surface. Two important design rules for both single- and multi-junction solar cells are established: i) the optimal junction thickness decreases and the optimal bandgap energy increases when nonradiative recombination increases; and ii) the optimal junction thickness increases and the optimal bandgap energy decreases for higher solar concentrations.

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Section: Auger Loss Energy Lost To Auger Recombinationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A semi-analytical model for semiconductor solar cells

Ding

Johnson

et al. 2011

Journal of Applied Physics

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“…In the presence of a non-flat slope around the operating point (i.e., in the presence of low shunt resistance), the EQE magnitude would be lower than expected. Traditionally, it has been attributed a low shunt resistance to the Ge subcell because of its low bandgap [8,13], thus justifying the need of V¡,i as and special light bias conditions during its EQE characterization [8,13]. While it might be true in some cases, we believe that, in state-of-the-art triple-junction, solar cells grown by highly mature MOVPE processes low shunt resistances are less common.…”

Section: Low Vpf Versus Shunt Resistance and Luminescent Coupling As mentioning

confidence: 93%

“…This artifact consists of a lower than expected EQE of the subcell under test plus the simultaneous measurement of some response in wavelengths corresponding to another subcell. The origin of the so-called measurement artifact has been thoroughly discussed in recent years and has been related to a variety of causes such as a low shunt resistance in any junction [8,9], luminescent coupling [10][11][12] or a combination of both [13]. In brief, these papers show that the EQE of a subcell is not only determined by its own properties but also by the electro-optical interactions with other subcells in the stack.…”

Section: Introductionmentioning

confidence: 99%

Implications of low breakdown voltage of component subcells on external quantum efficiency measurements of multijunction solar cells

Barrigón

Espinet‐González

Contreras

et al. 2015

Progress in Photovoltaics

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The electrical and optical coupling between subcells in a multijunction solar cell affects its external quantum efficiency (EQE) measurement. In this study, we show how a low breakdown voltage of a component subcell impacts the EQE determination of a multijunction solar cell and demands the use of a finely adjusted external voltage bias. The optimum voltage bias for the EQE measurement of a Ge subcell in two different GalnP/GalnAs/Ge triple-junction solar cells is determined both by sweeping the external voltage bias and by tracing the I-V curve under the same light bias conditions applied during the EQE measurement. It is shown that the I-V curve gives rapid and valuable information about the adequate light and voltage bias needed, and also helps to detect problems associated with non-ideal I-V curves that might affect the EQE measurement. The results also show that, if a non-optimum voltage bias is applied, a measurement artifact can result. Only when the problems associated with a non-ideal I-V curve and/or a low breakdown voltage have been discarded, the measurement artifacts, if any, can be attributed to other effects such as luminescent coupling between subcells.

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“…8,23 In addition, the photocurrent generation due to light unabsorbed by the upper subcells is much smaller compared with the LC current generation. 24 Thus, we assumed that all of the photocurrent generation in the Ge bottom cell by GaAs middle cell excitation is due to the LC effect. Also, the voltage distribution of the limiting Ge bottom cell is considered spatially uniform since the tunnel diode in between the GaAs and Ge subcells is heavily doped.…”

Section: Quasi-two-dimensional Simulation Modelmentioning

confidence: 99%

Impact of optically nonuniform luminescence coupling effect to the limiting cell conversion efficiency in InGaP/GaAs/Ge triple junction solar cell

et al. 2017

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Abstract. The impact of nonuniform spatial distribution of the luminescence coupling (LC) effect to the limiting cell conversion efficiency of multijunction solar cells (MJSCs) has been investigated. For this purpose, the laser beam induced current distribution maps of the limiting bottom cell have been acquired experimentally under varying middle-to-bottom cell LC efficiencies. The minimum and the maximum LC efficiencies demonstrated were 8.5% and 69%, respectively. To further analyze the measurement results, a quasi-two-dimensional simulation model considering the spatially nonuniform nature of the LC effect has been developed. A good agreement between the simulation and the measurement results suggests that the nonuniform LC current distribution is induced by optical phenomena such as photon escape and internal reflection. This nonuniformity then causes the absolute conversion efficiency of the limiting cell to be reduced by 1.35% at maximum LC efficiency. This reduction, when suppressed, can yield higher limiting cell conversion efficiency, which in turn may improve the overall MJSC conversion efficiency.

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Combined Effects of Shunt and Luminescence Coupling on External Quantum Efficiency Measurements of Multijunction Solar Cells

Cited by 45 publications

References 7 publications

A semi-analytical model for semiconductor solar cells

A semi-analytical model for semiconductor solar cells

Implications of low breakdown voltage of component subcells on external quantum efficiency measurements of multijunction solar cells

Impact of optically nonuniform luminescence coupling effect to the limiting cell conversion efficiency in InGaP/GaAs/Ge triple junction solar cell

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