Plasma-initiated rehydrogenation of amorphous silicon to increase the temperature processing window of silicon heterojunction solar cells

Abstract

The dehydrogenation of intrinsic hydrogenated amorphous silicon (a-Si:H) at temperatures above approximately 300 °C degrades its ability to passivate silicon wafer surfaces. This limits the temperature of post-passivation processing steps during the fabrication of advanced silicon heterojunction or silicon-based tandem solar cells. We demonstrate that a hydrogen plasma can rehydrogenate intrinsic a-Si:H passivation layers that have been dehydrogenated by annealing. The hydrogen plasma treatment fully restores the effective carrier lifetime to several milliseconds in textured crystalline silicon wafers coated with 8-nm-thick intrinsic a-Si:H layers after annealing at temperatures of up to 450 °C. Plasma-initiated rehydrogenation also translates to complete solar cells: A silicon heterojunction solar cell subjected to annealing at 450 °C (following intrinsic a-Si:H deposition) had an open-circuit voltage of less than 600 mV, but an identical cell that received hydrogen plasma treatment reached a voltage of over 710 mV and an efficiency of over 19%.

Intrinsic Amorphous Silicon Bilayers for Effective Surface Passivation in Silicon Heterojunction Solar Cells: A Comparative Study of Interfacial Layers

“…It is known that the microstructure of a-Si:H thin layers is reorganized by the post-H 2 -plasma treatment. [52,53] In the bilayer configuration used in this work, the reorganization of the interfacial i 1 -layer must occur during the overlying i 2 -layer deposition with a H-diluted plasma. This means that the i 1 -layer in the asdeposited state could be an intermediate state and different from that in the completed cell.…”

SEM, EDX spectroscopy and real-time optical microscopy of electroformed silicon nitride-based light emitting memory device

“…However, surface roughening may be related also to the nanocrystallization of the Si-based films. It is well known that dehydrogenation of a-Si:H structure begin at temperatures above 300 • C [15] which is known to be exceeded during nanocrystallization [4,8]. Therefore, a high rate of hydrogen outburst can be expected from the structure during electroforming.…”

Defect engineering of p‐type silicon heterojunction solar cells fabricated using commercial‐grade low‐lifetime silicon wafers

“…Note that an in situ 30 seconds hydrogen plasma treatment at 250 C was performed directly after a-Si:H(i) deposition (on both sides) to improve the passivation quality at the a-Si:H(i)/c-Si interface. 92,93 Some of these wafers were then removed for characterisation as lifetime test structures whereas others were fabricated into cells. Figure 2 depicts the fabrication flow for SHJ lifetime test structures and full SHJ solar cells.…”