High Open-Circuit Voltage in Silicon Heterojunction Solar Cells

Conference · Mon Jan 01 04:00:00 EST 2007

OSTI ID:978496

Wang, Q; Page, M R; Iwaniczko, E; Xu, Y; Roybal, L; Bauer, R; Levi, D; Yan, Y; Wang, T; Branz, H M

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

Related Subjects

14 SOLAR ENERGY
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