Toward Better Understanding and Improved Performance of Silicon Heterojunction Solar Cells: Preprint

Conference · Sun Aug 01 04:00:00 EDT 2004

OSTI ID:15009889

Wang, T H; Page, M R; Iwaniczko, E; Levi, D H; Yan, Y; Branz, H M; Yelundur, V; Rohatgi, A; Bunea, G; Terao, A; Wang, Q

The double-sided silicon heterojunction (SHJ) solar cell is more appropriate for n-type crystal silicon (c-Si) wafers than for p-type c-Si wafers because there is a larger band offset to the valence band edge of hydrogenated amorphous silicon than to the conduction band edge. Thin intrinsic and doped hydrogenated amorphous silicon (a Si:H) double layers by hot-wire chemical vapor deposition (HWCVD) are investigated as passivation layers, emitters, and back-surface-field (BSF) contacts to both p- and n-type wafers. Passivation quality is studied by characterizing the SHJ solar cells and by photoconductive decay (PCD) minority-carrier lifetime measurements. The crystal-amorphous heterointerface is studied with real-time spectroscopic ellipsometry (RTSE) and high-resolution transmission electron microscopy (HRTEM) to detect phase change and material evolution, with a focus on better understanding the factors determining passivation effectiveness. A common feature in effective passivation, emitter, and BSF layers is immediate a-Si:H deposition and an abrupt and flat interface to the c-Si substrate. In this case, good wafer passivation or an excellent heterojunction is obtained, with a low interface recombination velocity (S) or a high open-circuit voltage (Voc). Voc greater than 640 mV, S less than 15 cm/sec, and efficiency of 14.8% have been achieved on polished p type Czochralski-grown (CZ) Si wafers. Collaboration between NREL and Georgia Tech resulted in a 15.7%-efficient HWCVD-deposited SHJ cell on non-textured FZ-Si with a screen-printed Al back surface field (BSF), the highest reported HWCVD SHJ cell. Collaboration between NREL and SunPower demonstrated that HWCVD a-Si:H passivation can be better than the conventional oxides, with a low surface recombination velocity of 42 cm/sec on textured n-type FZ-Si.

• Research Organization: National Renewable Energy Lab., Golden, CO (US)
• Sponsoring Organization: US Department of Energy (US)
• DOE Contract Number: AC36-99GO10337
• OSTI ID: 15009889
• Report Number(s): NREL/CP-520-36669
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
36 MATERIALS SCIENCE
CHEMICAL VAPOR DEPOSITION
CRYSTAL GROWTH
CRYSTALLINE SILICON
DECAY
DEFECT
DEVICE PROCESS
ELLIPSOMETRY
HETEROJUNCTIONS
IMPURITIES
MATERIALS AND PROCESSES
MICROELECTRONICS
MODULE
ORGANIC COMPOUNDS
PASSIVATION
PERFORMANCE
PHOTOVOLTAICS
PV
RECOMBINATION
SILICON
SILICON SOLAR CELLS
SOLAR CELLS
SOLAR ENERGY - PHOTOVOLTAICS
TRANSMISSION ELECTRON MICROSCOPY
VALENCE
VOLATILE MATTER