Indium Tin Oxide-Free Polymer Solar Cells: Toward Commercial Reality - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 193

Fig. 6 Flowchart illustrating the classification of alternatives to ITO

where R sh is the sheet resistance, A is the absorbance, and t is the film thickness.
For thin films, this equation equates to G s A ; where G sh is the sheet conductance.
Alternatively,

r

a for thin films such as inorganic oxides in terms of transmittance
T and reflectance R can be written as [ 13 ];

r
a ¼ ffi R sh In T þ R

g ffi 1 f ð Þ ð 3 Þ

where T is the total visible transmittance and R is the total visible reflectance. Note
that these equations do not take into account the percolation nature of nanowires
and carbon nanotubes.
For an ITO film with an R sh of 6 X! -1 and an absorption coefficient of 0.04,
figure of merit ratio is 4. According to Eq. ( 1 ), a

r

a 1 is found necessary for
minimum power losses in various upscaling geometries of thin film solar cells
shown in Fig. 7 [ 12 ]. This corresponds to a T of 90 % and a R sh of 10 X! -1 .
Values lower than this would result in precipitous loses in the efficiency of
monolithically integrated modules than in single cells (Fig. 7 ). Monolithically
integrated modules are used in thin films inorganic and in PSCs, and are the more
cost-effectively produced designs that require no post processing assembly. Single
cells, on the other hand, demands labor-intensive post processing assembly and are
used in the first generation solar cells wherein silicon wafers are manually inter-
connected to produce a module.