Hydrogen diffusion mechanisms in silicon solar cells.

摘要

The diffusion of the element hydrogen into silicon solar cells has shown excellent results in the passivation of defects and impurities. Improvements in cell efficiency of 20% are seen by some PV manufacturers with the deep penetration of hydrogen, while others see no increase. This has motivated researchers in the past and present to understand the mechanism(s) of hydrogen diffusion in silicon solar cells. Therefore, we will study the diffusion mechanisms of hydrogen in as-grown substrates as well as in silicon solar cells to provide an explanation of why this increase in cell efficiency occurs by the deep penetration of hydrogen.;Based on past and present results, we established a model describing the diffusion mechanisms of hydrogen into silicon substrates by several techniques. The techniques used for this dissertation are a forming gas anneal, ion implantation, and a phosphorous diffusion during the creation of a solar cell. Common to all of these techniques is that they introduce a surface damage layer to the silicon substrates. We propose that initial diffusion takes place at the surface by a surface damage causing strain to the lattice structure. Fundamental experiments were executed in a low-temperature, forming gas atmosphere with an applied chemical-mechanical grit polish to verify this. We found that this surface damage layer provides a layer where the energy states are minimal. Thus, it is not difficult for molecular hydrogen to dissociate into the atomic form and diffuse into the silicon lattice as an H+ and an ;Thus, an explanation is given in this dissertation, from experimental results based on this diffusion model, describing mechanisms of hydrogen diffusion in silicon solar cells that provide excellent passivation of defects and impurities.