Chemistry Reference
In-Depth Information
[
270
], a private laboratory called
“Solamer” claimed, without disclosing details, to have achieved efficiency of 8.13%. They also stated
that they hope to achieve efficiency of 10% by end of 2011.
Syntheses of various polymers for solar cells were also reviewed by Cheng et al. [
271
] where they
point out that there is a need to develop better p-type materials that have good film properties and act
as very efficient chromophores, with good hole mobility and suitable molecular orbitals levels. They
also point out that magnitude of the band gap and the energy positions of the HOMO and LUMO
energy levels are the most important characteristics for determining the optical and electrical
properties of a given conjugated polymer. These, of course, will in turn greatly influence the ultimate
photovoltaic performance and conversion of light energy to electrical energy. The wavelength of the
maximum photon flux density of the solar spectrum is located at approximately 700 nm, which
corresponds to a low energy of 1.77 eV. The absorption spectrum of a conjugated polymer should
cover both the red and near-infra-red ranges to match the greater part of the terrestrial solar spectrum
and absorb the maximum photon flux. Thus, it is highly desirable to develop conjugated polymers
with broader absorptions through narrowing their optical band gap. At the same time, these materials
must efficiently absorb light. The overall high extinction coefficients of the polymers are also of
critical importance.
Following are presented some of the published results from recent and current research, to
illustrate the bulk of the effort in the field. The examples are chosen at random and there is no
implication that these are the best ones published to date.
Li and coworkers [
272
] reported synthesis and photovoltaic properties of three donor-acceptor
copolymers containing bithiazole acceptor. One of them was illustrated as follows:
According to a subsequent write up in
Chem. and Eng. News
C
8
H
17
H
17
C
8
N
N
S
S
n
S
S
N
The other two copolymers were similar. The copolymer that yielded the best results had the
carbazole replaced with the following molecule:
