Studying the nanostructure of a-Si:h solar cell absorber layers using positrion annihilation and neutron reflectometry

Studying the nanostructure of a-Si:h solar cell absorber layers using positrion annihilation and neutron reflectometry

Mannheim, A.

Melskens, J. (mentor)
Eijt, S. (mentor)

Applied Sciences

Applied Physics

2013-07-12

Hydrogenated Amorphous Silicon (a-Si:H) is a very promising solar cell material with a good potential to use in many applications, as it is cheap to produce, light-weight and flexible. However, upon prolonged exposure to light, the layers suffer from both metastable and irreversible changes (the Staebler-Wronski effect) that have a bad effect on the photoconductivity. Annealing the material up to 150-200oC removes the metastable changes. The Staebler-Wronski effect has been studied for over 35 years, but the mechanisms behind it are not fully understood yet. In this project an attempt is made to increase the understanding by examining the nanostructure of rf-PECVD produced a-Si:H samples, in particular the nanostructural evolution, as a function of annealing temperature (up to 800oC) and hydrogen dilution. Positron Annihilation Spectroscopy techniques, sensitive to even the smallest vacancies, are used to study the electron environment of the open volume defects. These techniques include Doppler broadening positron annihilation spectroscopy, two-dimensional angular correlation of annihilation radiation and coincidence Doppler broadening (DB-PAS, 2D-ACAR and CDB). Neutron Reflectometry is used to study the hydrogen content as a function of film depth. Raman spectroscopy is used in addition to the annealing experiment to detect the presence of molecular hydrogen. Clear evidence is found that dilution with hydrogen causes a broadening of the electron momentum distribution. DB-PAS and 2D-ACAR results strongly indicate that this broadening is due to a decrease in the average size of the open volume defects.

positron annihilation
PAS
DB-PAS
2D-ACAR
ACAR
CDB
nanostructure
metastable changes
vacancy
vacancy size
doppler broadening
hydrogen effusion
hydrogen distribution
vacancy agglomeration
neutron reflectometry
amorphous silicon
thin film solar cells
hydrogenated amorphous silicon
Staebler-Wronski effect
electron environment
open volume defects
Raman spectroscopy
crystallization
wing parameter
line shape parameter
solar cell absorber layers

http://resolver.tudelft.nl/uuid:5cc8024f-84a1-4edf-8123-fcd33d89f1fa

2013-12-05

Student theses

master thesis

(c) 2013 Mannheim, A.