Optical enhancement of the open-circuit voltage in high quality GaAs solar cells

Abstract

The self-absorption of radiated photons increases the minority carrier concentration in semiconductor optoelectronic devices such as solar cells. This so-called photon recycling leads to an increase in the external luminescent efficiency, the fraction of internally radiated photons that are able to escape through the front surface. An increased external luminescent efficiency in turn correlates with an increased open-circuit voltage and ultimately conversion efficiency. We develop a detailed ray-optical model that calculates Voc for real, non-idealized solar cells, accounting for isotropic luminescence, parasitic losses, multiple photon reflections within the cell and wavelength-dependent indices of refraction for the layers in the cell. We have fabricated high quality GaAs solar cells, systematically varying the optical properties including the back reflectance, and have demonstrated Voc = 1.101 ± 0.002 V and conversion efficiencies of (27.8 ± 0.8)% under the global solar spectrum. The trends shown by the model are in good agreement with the data.

Luminescent coupling in planar opto-electronic devices

“…Some researchers have used internal radiative efficiency as an input parameter to their models; 17,18 here, the internal radiative recombination is allowed to vary freely within each layer as a function of material parameters and operating conditions, but Fig. 4 shows that it was typically >90% in all GaAs layers for the SRH lifetime of s max ¼ 10 À4 s which matched the IQE of our sample 1.…”

Determination of CdTe bulk carrier lifetime and interface recombination velocity of CdTe/MgCdTe double heterostructures grown by molecular beam epitaxy

“…16 For CdTe, the absorption coefficient near the band edge is on the order of 10 4 cm À1 resulting in a short absorption length of the photons. The value of c for CdTe middle layer is calculated using the ray-tracing method 17 as shown in Fig. 2 and it increases as a function CdTe layer thickness.…”

Device characterization for design optimization of 4 junction inverted metamorphic concentrator solar cells

“…Indeed, the IRE (discussed next) results in unphysical values greater than unity if the EL is not corrected for LC effects. Optical modeling given accurate layer thicknesses and material constants n( ), k( ) allows a connection to be made between the internal and external radiative efficiency of the i th junction 12 ,…”