Abstract
AbstractIn this work, we develop a fabrication process for an interdigitated back contact solar cell using BBr3 diffusion to form the p+ region and POCl3 diffusion to form the n+ regions. We use the industry standard technology computer‐aided design modelling package, Synopsys Sentaurus, to optimize the geometry of the device using doping profiles derived from electrochemical capacitance voltage measurements. Cells are fabricated using n‐type float‐zone silicon substrates with an emitter fraction of 60%, with localized back surface field and contact holes. Key factors affecting cell performance are identified including the impact of e‐beam evaporation, dry etch damage, and bulk defects in the float zone silicon substrate. It is shown that a preoxidation treatment of the wafer can lead to a 2 ms improvement in bulk minority carrier lifetime at the cell level, resulting in a 4% absolute efficiency boost.
Highlights
The highest single‐junction silicon wafer solar‐cell power conversion efficiencies reported to date were achieved with the interdigitated back contact (IBC) architecture
We present findings on cell fabrication process improvements developed during the study, including overcoming problems caused by reactive ion etching (RIE) and by electron‐beam evaporation of metal contacts
Minority carrier lifetime analysis of the wafers showed a significant increase in the maximum effective lifetime from 460 μs to 1.8 ms due to the bulk FZ treatment
Summary
The highest single‐junction silicon wafer solar‐cell power conversion efficiencies reported to date were achieved with the interdigitated back contact (IBC) architecture. For IBC architectures where there are, in general, many high‐temperature processes, the material must maintain high bulk lifetimes throughout cell fabrication. We first use Sentaurus technology computer‐aided design (TCAD)[13] to design the geometry of the device prior to fabrication This determines the optimum emitter finger width and fraction as well as the diameter of localized back surface field (BSF) and contact holes. The contact finger widths (nCF and pCF) were kept the same as the doped region widths, with contact lumped series resistance (Rs) calculated using Grid[15] for the varying contact fraction
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