Environmental Engineering Reference
In-Depth Information
Fig. 17 A photograph of ITO-free PSC (2 9 2cm
2
) with screen-printed Ag grid and highly
conductive PEDOT: PSS as front electrode and evaporated Al back electrode (left). The device
comprised of a layer stack schematically shown alongside (right). These devices had similar
photovoltaic performance to ITO. 2013 Elsevier. Reprinted, from with permission from Ref.
[
106
]
radiation reaching the photoactive layer. Conductivity can be increasing by
increasing line height while maintaining minimum shading losses [
104
]. In gen-
eral, for a given PEDOT:PSS, the optimized geometry of the metal grid that results
in minimum shading fractional power losses is simply given by the empirical
relation (W/W+ S) where W is the grid width and S is the grid separation [
103
,
105
].
With rigorous optimizations of grid design and PEDOT:PSS thickness, the
composite metal grid and PEDOT:PSS transparent conductor layers have resulted
in a performance similar to ITO-based solar cells in both normal and inverted
device geometries [
103
,
104
,
106
] (Fig.
17
). Some methods used for deposition of
metal grids in laboratory cells are lithography [
103
,
107
,
108
]; thermal evaporation
through shadow masks [
109
-
111
]; sputtering in combination with photolithogra-
phy for patterning [
112
]; microfluidic deposition and nanoimprinting methods
[
104
]; precision-weaved metalized polymer fabric electrodes [
113
]; and printing
methods such as screen printing [
3
]; inkjet printing [
107
,
114
,
115
]; and flexo-
graphic printing [
115
]. Among all these methods, currently only the printing
methods are readily adoptable in a fast large-scale roll-to-roll processing of low-
cost PSC. These methods have been experimentally demonstrated as well.
In a normal structure, the use of screen-printed metal grids in combination with
highly conductive PEDOT:PSS on flexible substrates has shown superior PCE to
equivalent ITO-based cells [
106
]. Similarly, the use of inkjet-printed metal grid as
well as embedded grids in flexible substrates has also resulted in similar results
with higher reproducibility [
107
,
114
].
Top illuminated inverted structures have been also adopted in the demonstra-
tion of ITO-free large-area PSC modules in a structure: substrate/metal/buffer
layer/photoactive layer/PEDOT:PSS/Ag grid. The PEDOT:PSS/Ag grid forms the
Search WWH ::
Custom Search