TITLE:
Emitter Quality Optimization Using Lightly Doped Phosphorus Diffusion and Thermal Oxide Anneal for Cell Efficiency Improvement in Multi-Crystalline Black Silicon Solar Cells
AUTHORS:
Kishan Shetty, Yudhbir Kaushal, Nagesh Chikkaiah, Chandra Mauli Kumar
KEYWORDS:
Lightly Doped Emitter, Oxidation, Annealing, Metal Catalyst Chemical Etching, Phosphorus Silicate Glass, Diffusion
JOURNAL NAME:
Journal of Power and Energy Engineering,
Vol.10 No.3,
March
22,
2022
ABSTRACT: Improving solar cell performance by increasing solar cell efficiency by
various process optimization had always been a simple straight-forward
methodology followed in a R&D or in a solar cell manufacturing company.
This is also the most cost-effective practice to improve a product performance using the same
technology without the need to procure alternative or expensive raw materials
or by adopting advanced solar cell processing techniques. Aluminium Back
Surface Field (Al-BSF) technology using multi-crystalline wafers (mc-Si) had
been a well-established and a dominant product in the solar industry for more
than two decades. However, as the industry progresses, the demand for high
efficiency solar cells and modules started going up and full area Aluminium BSF
based cells suffers from a lot of inherent limitations on cell efficiency. This
is primarily due to the intrinsic high density of crystal lattice defects or
otherwise called as grain boundary defects present dominantly only in mc-Si
wafers. These grain boundaries tends to accumulate several defects and become
trap centres which cause high recombination for minority carriers thereby
exhibiting lower conversion efficiency and higher dispersion in electrical
parameters in batches of tested cells. Years of research using this material have helped
to derive the maximum benefits using this mc-Si wafer in producing industrial
full area BSF cells and we can say with certainty that the efficiency potential
has reached the saturation point with this technology. An interesting
development that happened in the area of improving the final product
performance using mc-Si wafers at both cell and module level, is by replacing
the conventional acid texturing process with an introduction of a nano-texturing
process called Metal Catalysed Chemical Etching (MCCE) using specialized chemicals which
improves the light trapping capabilities by creation of inverted pyramid
texture on the silicon wafer surface and thereby enabling the wafers to absorb
sunlight over a broader range of wavelength and incident angle. With this
development done in mc-Si wafers in recent past, it is still a daunting task to
surpass cell efficiencies beyond 19.0% using this wafer source. Hence for cell
manufacturing lines which use mc-Si wafers, there is always a constant need to
improve the cell manufacturing processes to reduce the impact of poor intrinsic
quality of mc-Si wafers and improve the final product performance without
adding any significant cost factor.