Impact of the growth temperature on the performance of 1.70-eV Al0.22Ga0.78As solar cells grown by MBE

Abstract

Growth of high material quality Aluminum Gallium Arsenide (AlxGa1-xAs) is known to be challenging, in particular with an Al content x above 20%. As a result, the use of AlxGa1-xAs in devices requiring high minority carrier lifetimes, such as solar cells, has been limited. Nonetheless, it has long been established that the substrate temperature is a key parameter in improving AlxGa1-xAs material quality. In order to optimize the growth temperature of 1.70-eV Al0.22Ga0.78As solar cells, five samples have been grown by Solid-Source Molecular Beam Epitaxy (SSMBE) at 580°C, 600°C, 620°C, 640°C, and 660°C, respectively. A strong improvement in performance is observed with increasing the growth temperature from 580°C to 620°C. An open-circuit voltage above 1.21V has in particular been demonstrated on the sample grown at 620°C, translating into a bandgap-voltage offset Woc below 0.5V. Above 620°C, performances -in particular the short-circuit current density -moderately decrease. This trend is confirmed by photoluminescence, current density versus voltage characterization under illumination, and external quantum efficiency measurements.

MBE growth of 1.7eV Al0.2Ga0.8As and 1.42eV GaAs solar cells on Si using dislocations filters: an alternative pathway toward III-V/ Si solar cells architectures

“…Recent work has focused on the improvement of the Al 0.2 Ga 0.8 As material quality by improving the growth conditions and in particular the substrate temperature. This optimization study has yielded a strong improvement of performances with increasing the growth temperature from 580°C to 620°C, with a V oc over 1.21V demonstrated [19]. Al 0.2 Ga 0.8 As solar cells epitaxially grown on Si with a V oc exceeding 1.0V are likely achievable by transferring this optimized Al 0.2 Ga 0.8 As growth recipe on Si.…”

1.73 eV AlGaAs/InGaP heterojunction solar cell grown by MBE with 18.7% efficiency

“…Both face the same challenge of improving material properties to raise efficiencies. For AlGaAs cells, incremental growth optimization of the alloy led to short circuit current ( J sc ) improvements . The reduction of defect concentrations related to the formation of DX‐centers resulted in state‐of‐the‐art AlGaAs solar cells with a bandgap around 1.7 eV and efficiencies up to 16.9 %, with best results achieved by MOVPE.…”

“…For AlGaAs cells, incremental growth optimization of the alloy led to short circuit current (J sc ) improvements. 21 The reduction of defect concentrations related to the formation of DX-centers resulted in state-of-the-art AlGaAs solar cells with a bandgap around 1.7 eV and efficiencies up to 16.9 %, 22 with best results achieved by MOVPE. For InGaP cells, growth temperature tuning led to efficiencies up to 16.6% for MBE grown single junction solar cell.…”

AlGaAs/InGaP MBE-grown heterostructures for 1.73eV Solar Cells With 18.7% Efficiency

“…On the other hand, despite its bandgap flexibility, researchers quickly lost interest in AlGaAs potential due to oxygen contamination during the growth. Best results with AlGaAs cells were achieved by MOVPE, reaching efficiencies of 16.9% for bandgaps near 1.7eV [12], [13].…”