Low Cost Thin Film Building-Integrated PV Systems: Cooperative Research and Development Final Report, CRADA Number CRD-07-239 Page: 5 of 6
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Sdm cFig.2. Hydrogen effusion time profiles for four
different nc-Si:H solar cells. Samples A and C have
low crystalline volume fraction while B and C are
highly crystalline (Ref. [2]).200 300 400 500 600 700
Temperature ("C)2. Reducing Staebler-Wronski effect in a-Si:H. Hydrogen is considered to be strongly related to the
cause of the Staebler-Wronski effect in a-Si:H, however it's detailed role has not been revealed [3]. In
our recent experiments, we intentionally manipulated the H bonding environments by controlled, post-
deposition thermal treatments [3] in device-quality a-Si:H. Just at the onset of H effusion between 350
0C and 400 C, those treatments result in remarkable suppression of SWE: the total Si dangling bond
defect concentration is 2x lower in treated sample after prolonged degradation by laser pulses, while
the light-induced defects alone were suppressed by factor of five [3,4] (see Fig.2)._* uintreated
" 400 -
* -
4 1---i4
- 0
_ untreated
*400 C1 Exposure Time (hours)
8
Fig. 2. Top panel: Total Si dangling bond defect
spin density (solid symbols) and defect absorption
(open symbols) in as-deposited (squares) and
400C treated a-Si:H (circles) as function of laser
light exposure time. Bottom: the accumulation of
light-induced only defect spins (Ref. [31).Proton NMR line narrows as a result of the thermal post-deposition treatments [4], indicating that
hydrogen becomes less clustered in the nanovoids. This, together with small-angle X-ray scattering
(SAXS) literature data [S. Acco et al., Phys. Rev. B 58, 12853 - 12864 (1998)], suggests that changes in H
bonding and in Si network nanostructure are responsible for the reduced SWE. In particular, atomic-size
void coalescence, accompanied by restructuring of the inner surfaces of resulting larger nanovoids might
be responsible. Eliminating the atomic-size hydrogenated voids seems to strongly reduce SWE. The post-
deposition annealing treatments, while still challenging to implement into devices, show a clear proof of
concept for a SWE-free a-Si:H and reveal a critical metric (hydrogenated void nanostructure) to
eliminate the SWE.3
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Stradins, P. Low Cost Thin Film Building-Integrated PV Systems: Cooperative Research and Development Final Report, CRADA Number CRD-07-239, report, October 1, 2011; Golden, Colorado. (https://digital.library.unt.edu/ark:/67531/metadc833480/m1/5/: accessed May 3, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.