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Thorough subcells diagnosis in a multi-junction solar cell via absolute electroluminescence-efficiency measurements.

Chen S, Zhu L, Yoshita M, Mochizuki T, Kim C, Akiyama H, Imaizumi M, Kanemitsu Y - Sci Rep (2015)

Bottom Line: Here, we propose a potential standard method to quantify the detailed subcell properties of multi-junction solar cells based on absolute measurements of electroluminescence (EL) external quantum efficiency in addition to the conventional solar-cell external-quantum-efficiency measurements.We demonstrate that the absolute-EL-quantum-efficiency measurements provide I-V relations of individual subcells without the need for referencing measured I-V data, which is in stark contrast to previous works.Moreover, our measurements quantify the absolute rates of junction loss, non-radiative loss, radiative loss, and luminescence coupling in the subcells, which constitute the "balance sheets" of tandem solar cells.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute for Solid State Physics, University of Tokyo, and JST-CREST, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan [2] Department of Electronic Engineering, East China Normal University, 500 Dongchuan Road, Shanghai 200241, China.

ABSTRACT
World-wide studies on multi-junction (tandem) solar cells have led to record-breaking improvements in conversion efficiencies year after year. To obtain detailed and proper feedback for solar-cell design and fabrication, it is necessary to establish standard methods for diagnosing subcells in fabricated tandem devices. Here, we propose a potential standard method to quantify the detailed subcell properties of multi-junction solar cells based on absolute measurements of electroluminescence (EL) external quantum efficiency in addition to the conventional solar-cell external-quantum-efficiency measurements. We demonstrate that the absolute-EL-quantum-efficiency measurements provide I-V relations of individual subcells without the need for referencing measured I-V data, which is in stark contrast to previous works. Moreover, our measurements quantify the absolute rates of junction loss, non-radiative loss, radiative loss, and luminescence coupling in the subcells, which constitute the "balance sheets" of tandem solar cells.

No MeSH data available.


Absolute EL measurement of the 3-junction solar cell.(a). Schematic of the experimental setup for the absolute EL measurement of the solar cell. The top panel presents a photograph of the solar cell without and with injection current (15 mA/cm2). (b). Schematic structure of the GaInP/GaAs/Ge 3-junction solar cell. (c). Absolute EL spectra divided by injection-electron number (abs. EL efficiency) for various injection-current densities of the triple-junction solar cell. (d). The measured external EL quantum efficiencies (ext. EL. quan. efficiency) of the subcells under the operation of an LED (yextLED) as a function of the injection-current density. Note that the y-axis of the EL spectra is the absolute photon number per second divided by the injection carrier number per second, i.e., the y-axis represents the external EL quantum efficiency (yextLED) as a function of the photon energy. Consequently, the yextLED of the subcells (Fig. 1d) can be obtained through the integrations of the EL peaks in the EL spectra.
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f1: Absolute EL measurement of the 3-junction solar cell.(a). Schematic of the experimental setup for the absolute EL measurement of the solar cell. The top panel presents a photograph of the solar cell without and with injection current (15 mA/cm2). (b). Schematic structure of the GaInP/GaAs/Ge 3-junction solar cell. (c). Absolute EL spectra divided by injection-electron number (abs. EL efficiency) for various injection-current densities of the triple-junction solar cell. (d). The measured external EL quantum efficiencies (ext. EL. quan. efficiency) of the subcells under the operation of an LED (yextLED) as a function of the injection-current density. Note that the y-axis of the EL spectra is the absolute photon number per second divided by the injection carrier number per second, i.e., the y-axis represents the external EL quantum efficiency (yextLED) as a function of the photon energy. Consequently, the yextLED of the subcells (Fig. 1d) can be obtained through the integrations of the EL peaks in the EL spectra.

Mentions: Figure 1a presents a schematic of the solar-cell sample and the EL measurement. The two photographs show the solar cell without and with a forward-bias injection current, where the solar-cell device is operated as a LED for the EL measurement. Figure 1b presents the schematic structure of the tandem GaInP/GaAs/Ge 3-junction solar cell. Figure 1c presents the measured absolute EL spectra (above 1.2 eV) of the solar cell with various injection-current densities. The photon energies (1.40 and 1.81 eV) of the two EL peaks correspond to the bandgap energies of the middle (GaAs) and top (GaInP) subcells. Note that the two peaks have an intensity difference of approximately a factor of 10, and the dependences on the injection current also differ. Figure 1d shows the measured external EL quantum efficiency yextLED = qRext_i→0/JLED of the top (i = 1), middle (i = 2), and bottom (i = 3) subcells, plotted on a log scale as functions of the injection current density JLED, where Rext_i→0 is the external radiative emission rate of the subcell. It is demonstrated that yextLED of all the subcells increases gradually with increasing injection-current density, which indicates an increased radiative recombination rate at increased carrier densities in the subcells3132.


Thorough subcells diagnosis in a multi-junction solar cell via absolute electroluminescence-efficiency measurements.

Chen S, Zhu L, Yoshita M, Mochizuki T, Kim C, Akiyama H, Imaizumi M, Kanemitsu Y - Sci Rep (2015)

Absolute EL measurement of the 3-junction solar cell.(a). Schematic of the experimental setup for the absolute EL measurement of the solar cell. The top panel presents a photograph of the solar cell without and with injection current (15 mA/cm2). (b). Schematic structure of the GaInP/GaAs/Ge 3-junction solar cell. (c). Absolute EL spectra divided by injection-electron number (abs. EL efficiency) for various injection-current densities of the triple-junction solar cell. (d). The measured external EL quantum efficiencies (ext. EL. quan. efficiency) of the subcells under the operation of an LED (yextLED) as a function of the injection-current density. Note that the y-axis of the EL spectra is the absolute photon number per second divided by the injection carrier number per second, i.e., the y-axis represents the external EL quantum efficiency (yextLED) as a function of the photon energy. Consequently, the yextLED of the subcells (Fig. 1d) can be obtained through the integrations of the EL peaks in the EL spectra.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4296303&req=5

f1: Absolute EL measurement of the 3-junction solar cell.(a). Schematic of the experimental setup for the absolute EL measurement of the solar cell. The top panel presents a photograph of the solar cell without and with injection current (15 mA/cm2). (b). Schematic structure of the GaInP/GaAs/Ge 3-junction solar cell. (c). Absolute EL spectra divided by injection-electron number (abs. EL efficiency) for various injection-current densities of the triple-junction solar cell. (d). The measured external EL quantum efficiencies (ext. EL. quan. efficiency) of the subcells under the operation of an LED (yextLED) as a function of the injection-current density. Note that the y-axis of the EL spectra is the absolute photon number per second divided by the injection carrier number per second, i.e., the y-axis represents the external EL quantum efficiency (yextLED) as a function of the photon energy. Consequently, the yextLED of the subcells (Fig. 1d) can be obtained through the integrations of the EL peaks in the EL spectra.
Mentions: Figure 1a presents a schematic of the solar-cell sample and the EL measurement. The two photographs show the solar cell without and with a forward-bias injection current, where the solar-cell device is operated as a LED for the EL measurement. Figure 1b presents the schematic structure of the tandem GaInP/GaAs/Ge 3-junction solar cell. Figure 1c presents the measured absolute EL spectra (above 1.2 eV) of the solar cell with various injection-current densities. The photon energies (1.40 and 1.81 eV) of the two EL peaks correspond to the bandgap energies of the middle (GaAs) and top (GaInP) subcells. Note that the two peaks have an intensity difference of approximately a factor of 10, and the dependences on the injection current also differ. Figure 1d shows the measured external EL quantum efficiency yextLED = qRext_i→0/JLED of the top (i = 1), middle (i = 2), and bottom (i = 3) subcells, plotted on a log scale as functions of the injection current density JLED, where Rext_i→0 is the external radiative emission rate of the subcell. It is demonstrated that yextLED of all the subcells increases gradually with increasing injection-current density, which indicates an increased radiative recombination rate at increased carrier densities in the subcells3132.

Bottom Line: Here, we propose a potential standard method to quantify the detailed subcell properties of multi-junction solar cells based on absolute measurements of electroluminescence (EL) external quantum efficiency in addition to the conventional solar-cell external-quantum-efficiency measurements.We demonstrate that the absolute-EL-quantum-efficiency measurements provide I-V relations of individual subcells without the need for referencing measured I-V data, which is in stark contrast to previous works.Moreover, our measurements quantify the absolute rates of junction loss, non-radiative loss, radiative loss, and luminescence coupling in the subcells, which constitute the "balance sheets" of tandem solar cells.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute for Solid State Physics, University of Tokyo, and JST-CREST, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan [2] Department of Electronic Engineering, East China Normal University, 500 Dongchuan Road, Shanghai 200241, China.

ABSTRACT
World-wide studies on multi-junction (tandem) solar cells have led to record-breaking improvements in conversion efficiencies year after year. To obtain detailed and proper feedback for solar-cell design and fabrication, it is necessary to establish standard methods for diagnosing subcells in fabricated tandem devices. Here, we propose a potential standard method to quantify the detailed subcell properties of multi-junction solar cells based on absolute measurements of electroluminescence (EL) external quantum efficiency in addition to the conventional solar-cell external-quantum-efficiency measurements. We demonstrate that the absolute-EL-quantum-efficiency measurements provide I-V relations of individual subcells without the need for referencing measured I-V data, which is in stark contrast to previous works. Moreover, our measurements quantify the absolute rates of junction loss, non-radiative loss, radiative loss, and luminescence coupling in the subcells, which constitute the "balance sheets" of tandem solar cells.

No MeSH data available.