研究目的
Investigating the efficiency improvements of AlGaAs-based heterojunction solar cells grown by solid source molecular beam epitaxy (MBE) by combining a thick p-AlGaAs base with tunable bandgap and a thin n-InGaP emitter.
研究成果
The combination of a thick p-Al0.25Ga0.75As base layer with a thin n-InGaP emitter layer provides a way to increase carrier mobilities and to reduce the impact of DX-centers. This heterojunction design resulted in a certified efficiency of 18.7% at a bandgap of 1.73 eV, perfectly suited for Si-based tandem devices. Higher efficiencies can be achieved with further growth optimization, double ARC and back mirror.
研究不足
The study is limited by the material quality of n-AlGaAs and p-InGaP, which affects the solar cell efficiencies. The growth temperature in MBE is lower than in MOVPE, resulting in more defect states and deep centers.
1：Experimental Design and Method Selection:
The study focuses on the growth of AlGaAs-based heterojunction solar cells by MBE, investigating the material quality of InGaP and AlGaAs. The methodology includes the combination of a thick p-AlGaAs base with a tunable bandgap and a thin n-InGaP emitter separated by a thin intrinsic AlGaAs layer.
2：Sample Selection and Data Sources:
The samples are AlGaAs-based heterojunction solar cells grown by MBE. The data sources include certified solar cell conversion efficiency measurements and material quality assessments.
3：List of Experimental Equipment and Materials:
The epitaxial growth was performed with a RIBER compact 21 solid-source MBE machine equipped with arsenic and phosphorous-valved cracker cells. Standard p-type GaAs (100) substrates were used.
4：Experimental Procedures and Operational Workflow:
The growth rates are approximately 1 μm/h for GaAs and Al0.51GaAs and 0.5 μm/h for the other layers. The typical growth conditions are a beam-equivalent pressure (BEP) of 1 × 10?5 Torr with a V/III ratio of 20 at 550°C for arsenic-based layers and a V/III ratio of 8 at 500°C for phosphorus-based layers.
5：51GaAs and 5 μm/h for the other layers. The typical growth conditions are a beam-equivalent pressure (BEP) of 1 × 10?5 Torr with a V/III ratio of 20 at 550°C for arsenic-based layers and a V/III ratio of 8 at 500°C for phosphorus-based layers.
Data Analysis Methods:
5. Data Analysis Methods: The solar cell performances were analyzed using I-V characteristics under AM1.5G illumination, external quantum efficiency (EQE) measurements, and photoluminescence spectroscopy.
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