Effect of band mismatch on minority carrier transport in heterojunction solar cells

• Hole motion through the heterointerface in crystalline/amorphous Si solar cells.
• Band mismatch leads to asymmetrical carrier transport in opposing directions.
• Minority carriers accumulate on the low-energy side of the heterointerface.
• Accumulation causes an electrostatic potential to retard further carrier transport.

By using transient-capacitance techniques we probe the mechanism of hole transport in amorphous/crystalline silicon heterojunction solar cells. The devices are formed by depositing undoped amorphous silicon followed by p-type amorphous silicon on n-type crystalline silicon wafers. The capacitance transients indicate that hole transport from p-type amorphous silicon to n-type crystalline silicon is hindered by hole accumulation in the depletion region of the crystalline silicon. The results are explained with a model based on electrostatic repulsion owing to hole build-up at the crystalline/amorphous interface. We apply these results to other heterojunction solar cells.

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