Frequency response of the external quantum efficiency in multijunction solar cells

Abstract

The frequency dependence of the external quantum efficiency (EQE) of high-quality multijunction solar cells was examined by the modulated photocurrent spectroscopy method via an optical setup comprised of a light-pipe-coupled compact LED array. The optical excitation was achieved through sinusoidal electrical modulation of an appropriate LED by a custom-designed, high bandwidth amplifier. We observed unique features in the amplitude and phase data of the EQE frequency sweeps that are very sensitive to various subcell parameters and light bias conditions. These features are discussed extensively within the context of an AC equivalent circuit model, showing remarkable agreement between the experimental data and the proposed model.

Potential of subdermal solar energy harvesting for medical device applications based on worldwide meteorological data

“…This can be achieved using other semiconductor materials or using quantum dots. 31 An adapted double junction GaAs-GaInNAs solar cell would show high efficiency in the wavelength range of 650 to 1200 nm, 32 which is more suitable for subdermal applications. Figure 7 shows a comparison of the normalized standard irradiation ASTMG173, the resulting subdermal fluence rate for light and skin type VI and the external quantum efficiencies of monocrystalline solar cells and the adapted GaAs-GaInNAs multilayer cell.…”

The effect of luminescent coupling on modulated photocurrent measurements in multijunction solar cells

“…Traditionally, currentvoltage (I-V) measurements, 11,13,14 light bias and voltage bias dependent external quantum efficiency measurements (EQE), [18][19][20][21][22] and electroluminescent measurements 23,24 have been the methods of choice for studying shunt resistance artifacts, 16,21,22,25,26 reverse breakdown voltage 27,28 and luminescent coupling (LC) effects 12,15,[29][30][31] in MJSCs, but recently new methods have also been presented. 32,33 The modulated photocurrent spectroscopy (MPCS) method probes the frequency dependence of the ac photogenerated current in response to modulated light excitation. This technique has recently been used to reveal how light biasing of various junctions affect the apparent quantum efficiency of each junction as a function of the excitation frequency.…”

“…This technique has recently been used to reveal how light biasing of various junctions affect the apparent quantum efficiency of each junction as a function of the excitation frequency. 32 For the sake of simplicity and narrow focus, previous studies 32 selected the device operation point to minimize light coupling effects. However, the presence of LC in the MPCS signal is very pronounced for light bias values near 1-sun equivalent intensity.…”

“…The general solution for the circuit-extracted current, I sc , in terms of the relevant parameters can be found by applying Kirchhoff's current and voltage laws to the circuit. 32 The final result is shown in Eq. 1:…”

“…This approach gives us good confidence on the uniqueness of the reported fit parameters. 32 The low frequency data for each curve allows for extraction of the two LC coupling efficiencies, η 1 and η 2 , as shown by Eqs. 4 and…”