Impact of photon recycling and luminescence coupling in III-V photovoltaic devices

Abstract

Single junction photovoltaic devices composed of direct bandgap III-V semiconductors such as GaAs can exploit the effects of photon recycling to achieve record-high open circuit voltages. Modeling such devices yields insight into the design and material criteria required to achieve high efficiencies. For a GaAs cell to reach 28 % efficiency without a substrate, the Shockley-Read-Hall (SRH) lifetimes of the electrons and holes must be longer than 3 s and 100 ns respectively in a 2 m thin active region coupled to a very high reflective (>99%) rear-side mirror. The model is generalized to account for luminescence coupling in tandem devices, which yields direct insight into the top cell's non-radiative lifetimes. A heavily current mismatched GaAs/GaAs tandem device is simulated and measured experimentally as a function of concentration between 3 and 100 suns. The luminescence coupling increases from 14 % to 33 % experimentally, whereas the model requires an increasing SRH lifetime for both electrons and holes to explain these experimental results. However, intermediate absorbing GaAs layers between the two sub-cells may also increasingly contribute to the luminescence coupling as a function of concentration.

Measurement of strong photon recycling in ultra‐thin GaAs n/p junctions monolithically integrated in high‐photovoltage vertical epitaxial heterostructure architectures with conversion efficiencies exceeding 60%

“…Therefore, a V oc enhancement in devices based on nano‐scale layers may be expected compared to devices based on more standard bulk layers. Furthermore, high photovoltages and conversion efficiencies have been reported with GaAs side by side planar or vertical arrangements, in particular at high optical intensities with light management or in other material systems . Moreover, record‐high photovoltages and unprecedented monochromatic conversion efficiencies have now been demonstrated for phototransducer applications with the vertical epitaxial heterostructure architecture (VEHSA) design which is engineered with multiple thin, partially absorbing, subcells of the same material .…”

Luminescent coupling in planar opto-electronic devices

“…4 Letay et al have also modelled photon recycling effects in single junctions within a drift-diffusion simulator, using an iterative approach which involves running the simulator repeatedly with successive approximations of the coupled photocurrent. [5][6][7][8] Luminescent coupling has also been incorporated into simulations of light-emitting diodes. 9 In this work, we present a photovoltaic device with five monolithically integrated GaAs junctions displaying strong effects attributed to luminescent coupling.…”

D1.4 - Photovoltaic Cells with Increased Voltage Output for Optical Power Supply of Sensor Electronics

“…Finally, it is remarked that the current mismatch in multi-junction laser power converters can be counterbalanced by an effect known as luminescence coupling [27]. If carriers which are generated in the overproducing subcells recombine radiatively, they emit a photon which can be reabsorbed by adjacent subcells.…”