Environmental Engineering Reference
In-Depth Information
Fig. 1 Various future applications of the Polymer Solar Cells with a large-scale and flexible
advantages.
(The
images
captured
at
Copyright
Solarmer Energy Inc)
roofs, and windows as shown in Fig.
1
. The manufacturing processes of polymer
solar cells are relatively environmentally friendly due to low-emission and waste
free features. On the other hand, Polymer LEDs are strong contenders for low-cost
and flexible solid-state lighting.
Since the pioneering work of Tang [
1
], the OLEDs field has witnessed rapid
progress. The introduction of triplet phosphorescence materials by Forrest and
Thompson [
2
] has enabled commercialization of small molecule-based OLEDs. In
the OPVs area, after the introduction of the bi-layer heterojunction structure by
Tang in 1986, the efficient photo-induced charge transfer between conjugated
polymer and fullerene in the bulk heterojunction (BHJ) structure was reported by
Heeger et al. in 1992 [
3
]. The power conversion efficiency of the polymer (PBHJ)
solar cells has now increased to over 10 % by employing the low band gap
polymer [
4
].
To enable large manufacturing, however, there are few reports on high effi-
ciency OPVs devices fabricated by practical processing. There are some consid-
erations for developing fully printable solar cells. First, the materials should be
soluble in common solvents and stable in the air environment. Second, the device
structure should be simple and the film thickness should not be too thin consid-
ering the variability in film thickness in large area fabrication. If the device
structure contains many layers, the limitations and compatibility of solvents for
each functional layer should be considered due to the dissolution or intermixing
problems with the underlying layers. Thinner layers, e.g., of only a few nano-
meters thickness, are very challenging to realize uniform film thickness in the large
area devices. Third, the cost of the process and that of materials and substrates
should not be too expensive. For example, material utilization is low in both
vacuum evaporation and spin-coating deposition methods, and the former also
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