Abstract
The thermal stability of Mo thin films is indispensable to Cu(In,Ga)Se 2 (CIGS) solar cells: CIGS films are deposited above 500 °C. The thermal stabilities of Mo thin films with dense to porous Mo microstructures, which are varied by controlling the sputtering pressure, are investigated. Interface failures are found to occur in buckling mode in denser Mo films, whereas cracking arises in less dense films. The failure modes are apparently dependent on the sign of the residual stress: the former is due to compressive stress, whereas the latter is due to tensile stress. Interestingly, the softening of soda-lime glass at high temperatures reconfigures the film stresses to be more compressive after annealing, which in turn triggers buckling even in films that are tensile-stressed in the as-deposited states. We conclude that the appropriate processing conditions for thermally stable back contacts cannot be obtained with the simple single layer approach. On the basis of this relationship between microstructure, residual stress and the failure modes, it is shown that improvements in film adhesion can widen the processing window for the preparation of robust back contacts, i.e. with a conventional bilayer approach and substrate roughening. Since the bilayer approach employed more compliant porous structures in the bottom layer, back contacts that are better suited to higher stress and temperature can be produced. Furthermore, substrate roughening might make the back contact more conductive as well as more stable because adhesion can be enhanced without the use of an electrically resistive buffer layer.
| Original language | English |
|---|---|
| Article number | 425302 |
| Journal | Journal of Physics D: Applied Physics |
| Volume | 44 |
| Issue number | 42 |
| DOIs | |
| Publication status | Published - 2011 Oct 26 |
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ASJC Scopus subject areas
- Condensed Matter Physics
- Electronic, Optical and Magnetic Materials
- Acoustics and Ultrasonics
- Surfaces, Coatings and Films
Cite this
High-temperature stability of molybdenum (Mo) back contacts for CIGS solar cells : A route towards more robust back contacts. / Yoon, Ju Heon; Yoon, Kwan Hee; Kim, Won Mok; Park, Jong Keuk; Baik, Young Joon; Seong, Tae Yeon; Jeong, Jeung Hyun.
In: Journal of Physics D: Applied Physics, Vol. 44, No. 42, 425302, 26.10.2011.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - High-temperature stability of molybdenum (Mo) back contacts for CIGS solar cells
T2 - A route towards more robust back contacts
AU - Yoon, Ju Heon
AU - Yoon, Kwan Hee
AU - Kim, Won Mok
AU - Park, Jong Keuk
AU - Baik, Young Joon
AU - Seong, Tae Yeon
AU - Jeong, Jeung Hyun
PY - 2011/10/26
Y1 - 2011/10/26
N2 - The thermal stability of Mo thin films is indispensable to Cu(In,Ga)Se 2 (CIGS) solar cells: CIGS films are deposited above 500 °C. The thermal stabilities of Mo thin films with dense to porous Mo microstructures, which are varied by controlling the sputtering pressure, are investigated. Interface failures are found to occur in buckling mode in denser Mo films, whereas cracking arises in less dense films. The failure modes are apparently dependent on the sign of the residual stress: the former is due to compressive stress, whereas the latter is due to tensile stress. Interestingly, the softening of soda-lime glass at high temperatures reconfigures the film stresses to be more compressive after annealing, which in turn triggers buckling even in films that are tensile-stressed in the as-deposited states. We conclude that the appropriate processing conditions for thermally stable back contacts cannot be obtained with the simple single layer approach. On the basis of this relationship between microstructure, residual stress and the failure modes, it is shown that improvements in film adhesion can widen the processing window for the preparation of robust back contacts, i.e. with a conventional bilayer approach and substrate roughening. Since the bilayer approach employed more compliant porous structures in the bottom layer, back contacts that are better suited to higher stress and temperature can be produced. Furthermore, substrate roughening might make the back contact more conductive as well as more stable because adhesion can be enhanced without the use of an electrically resistive buffer layer.
AB - The thermal stability of Mo thin films is indispensable to Cu(In,Ga)Se 2 (CIGS) solar cells: CIGS films are deposited above 500 °C. The thermal stabilities of Mo thin films with dense to porous Mo microstructures, which are varied by controlling the sputtering pressure, are investigated. Interface failures are found to occur in buckling mode in denser Mo films, whereas cracking arises in less dense films. The failure modes are apparently dependent on the sign of the residual stress: the former is due to compressive stress, whereas the latter is due to tensile stress. Interestingly, the softening of soda-lime glass at high temperatures reconfigures the film stresses to be more compressive after annealing, which in turn triggers buckling even in films that are tensile-stressed in the as-deposited states. We conclude that the appropriate processing conditions for thermally stable back contacts cannot be obtained with the simple single layer approach. On the basis of this relationship between microstructure, residual stress and the failure modes, it is shown that improvements in film adhesion can widen the processing window for the preparation of robust back contacts, i.e. with a conventional bilayer approach and substrate roughening. Since the bilayer approach employed more compliant porous structures in the bottom layer, back contacts that are better suited to higher stress and temperature can be produced. Furthermore, substrate roughening might make the back contact more conductive as well as more stable because adhesion can be enhanced without the use of an electrically resistive buffer layer.
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U2 - 10.1088/0022-3727/44/42/425302
DO - 10.1088/0022-3727/44/42/425302
M3 - Article
VL - 44
JO - Journal Physics D: Applied Physics
JF - Journal Physics D: Applied Physics
SN - 0022-3727
IS - 42
M1 - 425302
ER -