High Open-Circuit Voltage in Silicon Heterojunction Solar Cells
High open-circuit voltage (V{sub oc}) silicon heterojunction (SHJ) solar cells are fabricated in double-heterojunction a-Si:H/c-Si/a-Si:H structures using low temperature (< 225 C) hydrogenated amorphous silicon (a-Si:H) contacts deposited by hot-wire chemical vapor deposition (HWCVD). On p-type c-Si float-zone wafers, we used an amorphous n/i contact to the top surface and an i/p contact to the back surface to obtain a V{sub oc} of 667 mV in a 1 cm{sup 2} cell with an efficiency of 18.2%. This is the best reported p-type SHJ voltage. In our labs, it improves over the 652 mV cell obtained with a front amorphous n/i heterojunction emitter and a high-temperature alloyed Al back-surface-field contact. On n-type c-Si float-zone wafers, we used an a-Si:H (p/i) front emitter and an a-Si:H (i/n) back contact to achieve a V{sub oc} of 691 mV on 1 cm{sup 2} cell. Though not as high as the 730 mV reported by Sanyo on n-wafers, this is the highest reported V{sub oc} for SHJ c-Si cells processed by the HWCVD technique. We found that effective c-Si surface cleaning and a double-heterojunction are keys to obtaining high Voc. Transmission electron microscopy reveals that high V{sub oc} cells require an abrupt interface from c-Si to a-Si:H. If the transition from the base wafer to the a-Si:H incorporates either microcrystalline or epitaxial Si at c-Si interface, a low V{sub oc} will result. Lifetime measurement shows that the back-surface-recombination velocity (BSRV) can be reduced to {approx}15 cm/s through a-Si:H passivation. Amorphous silicon heterojunction layers on crystalline wafers thus combine low-surface recombination velocity with excellent carrier extraction.
- Research Organization:
- National Renewable Energy Laboratory (NREL), Golden, CO.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 978496
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
CHEMICAL VAPOR DEPOSITION
EFFICIENCY
ELECTRIC POTENTIAL
HETEROJUNCTIONS
LIFETIME
ORGANIC COMPOUNDS
PASSIVATION
RECOMBINATION
SILICON
SOLAR CELLS
SURFACE CLEANING
Silicon Materials and Devices
Solar Energy - Photovoltaics
TRANSMISSION ELECTRON MICROSCOPY
VELOCITY
VOLATILE MATTER