Nitrogen based plasma processing for green photovoltaic cells

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Type
Thesis
Author
Lim, Mark Jian Wei
Supervisor
Xu, Shuyan
Abstract
Crystalline silicon based photovoltaic (PV) cells were fabricated through plasma processing in an integrated plasma photovoltaic nanofabrication cluster (IPPNC). The coupling of global energy demand with associated environmental problems has emphasized the need for renewable energy sources which are environmentally friendly and provide a sustainable future. In this work, ecofriendly nitrogen based plasma processes were utilized for nanofabrication of functional layers in a novel nitrogen doped emitter layer (NDEL) PV cell. An Ar + H2 plasma etch process removes surface damage and etches uniform nanotips on the surface of silicon, producing low-reflectivity (< 2%) black silicon. A N2 plasma immersion ion implantation process then produces an n-doped emitter layer through dense atomization of feedstock and implantation of atomic N into substrates. SiNx films were then deposited on the surface for reduction of reflective losses (<1.9 %), and to provide static charged films for reduction of surface recombination velocities. Minority carrier lifetime was enhanced through remote inductively coupled plasma assisted chemical vapour deposition of heavily B doped µc-Si films at the rear of the PV cell, giving rise to a back surface field effect passivation layer. Characterization of NDEL PV cells indicate fill factors ~70 %, Voc in the excess of 546 mV, and efficiencies reaching 13.3 %. Plasma diagnostics through insertion of electrostatic probes and non-invasive optical emission spectroscopy was also used to correlate plasma parameters to material properties to reveal plasma-surface reaction mechanisms and to allow for rapid upscaling. The developed processes and academic outputs of this work present numerous advantages over conventional methods through improving process controllability and uniformity at large scales. In-situ plasma diagnostics also allows operators to “dial in” recipes according to desired plasma parameters for device material specific requirements. Finally, the feedstocks used are environmentally friendly, illustrating a green method for nanofabrication of a novel form of renewable energy for a sustainable future.
Date Issued
2019
Call Number
QC715.4 Lim