Efficiency improvement in low temperature metal-oxide-semiconductor solar cells by thin metal film deposition on photon receiving area

Abstract

The recent discovery of the trap assisted tunneling property of low temperature liquid phase deposition (LPD) oxide is beneficial for metal-oxide-semiconductor (MOS) solar cells. Although the thickness of LPD oxide is up to 7 nm, the trap-assisted tunneling currents are still large enough for solar cell’s application. In this work, we fabricate and study the MOS solar cells with oxide prepared by LPD. The I–V curve for LPD oxide grown on bare Si is much different from that on native oxide. The larger tunneling current for LPD oxide grown on bare Si may be due to the boundaries between oxide seeds’ domains. For solar cells application, it’s better to use LPD oxide grown on bare Si. The conduction mechanism of LPD MOS solar cells is also discussed. For solar cells without additional thin transparent Al film, the minority carriers were collected from the accumulation region outside the main electrodes. For solar cells with additional thin transparent Al film, the thin Al electrode can directly collect the minority carriers from the weak inversion region underneath the thin Al film. For a cell exposed under 20 mW/cm2, short circuit current density JSC up to 13.2 mA/cm2, open circuit voltage VOC up to 433 mV, fill factor FF up to 66 and exposure area effective conversion efficiency η* up to 18.9% are obtained for this structure.