研究目的
Investigating the local open circuit voltage (VOC) at the nanoscale for monocrystalline Passivated Emitter Rear Contact (PERC) cells to understand their performance and degradation mechanisms.
研究成果
The study demonstrates a novel method for nanoscale resolution mapping of the open circuit potential (VOC) in solar cells, specifically at the rear electrode interface for Passivated Emitter Rear Contact (PERC) cells. The Al-doped p ?/p local back surface field is directly detected and found to uniformly extend * 2 um into the underlying p-type Si absorber. This method is uniquely capable of assessing the sensitivity to degradation of critical regions in PERC or other solar cells where relative current crowding occurs.
研究不足
The method is susceptible to topographic artifacts, with particular sensitivity to variations in local curvature. The actual photocurrents on conductors may be much higher than measured due to current-limiting by built-in protective circuitry. The measurement is also limited by the practical measurement times for high-resolution PV performance mapping.
1：Experimental Design and Method Selection:
The study employs Conductive Atomic Force Microscopy (cAFM) to directly detect the local VOC in monocrystalline PERC cells. The method involves a custom-configured proportional-integral-derivative loop during normal contact-mode AFM operation to constantly update the bias necessary to achieve null photocurrents, mimicking conventional open circuit potential mapping at AFM-probe dimensions.
2：Sample Selection and Data Sources:
Monocrystalline PERC cells prepared by the DuPont Silicon Valley Technology Center using conventional methods and implementing their Solamet metallization technology. The cells are based on M2 sized Longi p-type silicon wafers.
3：List of Experimental Equipment and Materials:
Customized AFM (Asylum Research mfp-3D, with ORCA integrated picoammeter) mounted on an inverted optical microscope platform (Nikon TE-2000), CREE high performance broadband LED for in situ front-surface light exposure, Leica EM TIC020 triple ion-beam cutter for sample preparation, Thermo Fisher Teneo LoVac SEM equipped with an EDAX EDXS system for SEM and EDS analysis.
4：Experimental Procedures and Operational Workflow:
The cells are cross-sectioned by conventional multi-beam argon ion polishing to expose local back surface field regions. The AFM probe serves as a local and scannable rear contact, maintaining force feedback and mapping local surface topography with nanoscale resolution.
5：Data Analysis Methods:
The approach involves direct acquisition of maps of VOC by mimicking conventional open circuit potential mapping, with data analyzed for variations in the magnitude and spatial extent of VOC around the entire circumference of a PERC via.
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