Spectral response measurements of each subcell in monolithic triple-junction GaAs photovoltaic devices

Abstract

Multijunction photovoltaic devices have gained attention for both solar cells and wireless power transmission. Herein, we present the spectral response of each subcell in a monolithic triple-junction photovoltaic device composed of only GaAs subcells with different thicknesses, which clarifies current matching among the GaAs subcells under simulated solar illumination conditions. In addition, the spectral response curves of each subcell show that the power-dependent spectral responses under laser illumination with wavelengths of 405, 660, and 785 nm are explained by the top GaAs subcell, which has a slightly lower shunt resistance and experiences the effects of luminescent coupling.

Experimental coupling process efficiency and benefits of back surface reflectors in photovoltaic multi‐junction photonic power converters

“…Two different phenomena may cause such deviations: luminescence coupling from overproducing subcells and parallel resistance artifacts caused by non‐infinite parallel resistance which lead to a higher output current from the limiting subcell when it operates at reverse voltages as consequence of the series connection. Both effects have been observed in multi‐junction cells of GaAs similar to the ones studied here [12, 33]. These effects feature different bias light dependences: whereas the parallel resistances artifact diminishes with increasing bias light intensity and thus current density, the luminescence coupling effect intensifies with increasing intensity because the device becomes more radiative.…”

A noval method of determining bias lights for spectral response measurement of GaAs multi-junction laser power converters and its applications

“…The measured EQE curves of the GaAs triple-junction LPC is illustrated in Figure 8. In the shorter wavelength range (400˜700nm), the corresponding EQE values of the 1st cell is the highest (the maximum value is about 58%), EQE of the 2nd cell is less and EQE of the 3rd cell is the least (near 0); whereas, in the longer wavelength range (830˜870nm), the corresponding EQE values of the 3rd cell is the highest (the maximum value is about 39%), EQE of the 2nd cell is less and EQE of the 1st cell is the least (less than 15%), which is consistent with the feature of the reported EQE curves of the GaAs triple-junction LPCs [38,39]. The measured EQE curves of the 1st cell, the 2nd cell, and the 3rd cell in the GaAs triple-junction LPC are all in good agreement with those obtained by simulation.…”

“…We first explain the principle of determining bias lights to make the interested sub-cell in GaAs MJLPCs current limiting. For any definite GaAs MJLPC, the photons at the short wavelengths are preferentially absorbed in the upper sub-cells due to the high absorption coefficient of GaAs semiconductors at these short wavelengths; while the photons with increased wavelengths, the penetration depth in the GaAs MJLPCs increases, and thus are mainly absorbed by the lower sub-cells [34][35][36][37][38][39]. Therefore, the upper sub-cell has a higher short-circuit current densityJ sc at shorter wavelengths, while the lower sub-cell has a higher J sc at longer wavelengths.…”

Beaming power: Photovoltaic laser power converters for power-by-light

“…Luminescence coupling only adds complexity to the EQE measurement, as it can interfere in the subcell current balancing. EQE measurements of VM-PVLPCs of up to 3 subcells are feasible (for example, using a combination of 500, 720, and 850 nm LED sources, see Figure 9, left) and have been reported, 102 but measuring all the subcells in devices with more junctions appears elusive.…”