reach the electrodes [33, 34]. All OPV efficiency records since have come from BHJ
style devices.
In 2003, Padinger and Sariciftci published a paper reporting a record OPV PCE
of 3.5% [35]. This was a huge improvement over the previous record of 2.5% [36],
but that was not what made the paper exciting. The exciting pieces of information
were:
1. More than one polymer (P3HT instead of MDMO-PPV) made effective OPV
devices
2. Choice of solvent and post-processing annealing conditions could greatly affect
the device efficiency
3. This improvement was most probably related to the microstructure
The first piece of information spurred a creative explosion in conjugated polymer synthesis that has produced numerous polymers yielding higher OPV efficiencies than P3HT [37–39]. The realization that morphology and device efficiency are
intimately related resulted in rapid advances in the use of new instrumentation to
study organic nanostructure [40, 41]. At the same time, further OPV device
efficiency increases were realized by the use of optimized morphology-controlling
strategies including the use of thermal annealing [42], solvent annealing [43], and
the application of various co-solvent additives [44, 45]. The most cited paper in all
of OPV research (>2,900 total) was published by Li et al. [43]. It demonstrated the
change in morphology associated with thermal and solvent annealing and was the
first published and certified efficiency record of over 4% for an OPV device.
Figure 3 shows J/V curves of P3HT:PCBM OPV devices from this seminal paper.
In the same month, two other groups also published >4% efficiency with P3HT:
PCBM but with different composition ratio, layer thickness, and annealing treatment [42, 46]. Although the OPV field has expanded widely beyond the P3HT:
PCBM system, P3HT:PCBM remains the “fruit fly” of OPV because the materials
are widely available with sufficient purity, and because all manner of new
processing techniques can be tested with the knowledge that small changes to the
microstructure yield large changes in OPV device PCE.
To demonstrate the pervasive study of P3HT as a model polymer for OPV, we
tracked the number of articles published about P3HT and OPV. In Fig. 1 we show
the number of scientific papers (as counted by Web of Knowledge) published per
year under the search terms “organic photovoltaic”, “P3HT”, and “organic
photovoltaic + P3HT”. This search shows that in 2013, more than 300 out of almost
1,700 OPV papers were searchable with P3HT as the OPV polymer, although P3HT
has not been a record polymer since 2006. Many of the other more than 500 P3HT
articles involve microstructural or photophysical studies that inform the OPV field.
188
A.J. Moule ´ et al.
style devices.
In 2003, Padinger and Sariciftci published a paper reporting a record OPV PCE
of 3.5% [35]. This was a huge improvement over the previous record of 2.5% [36],
but that was not what made the paper exciting. The exciting pieces of information
were:
1. More than one polymer (P3HT instead of MDMO-PPV) made effective OPV
devices
2. Choice of solvent and post-processing annealing conditions could greatly affect
the device efficiency
3. This improvement was most probably related to the microstructure
The first piece of information spurred a creative explosion in conjugated polymer synthesis that has produced numerous polymers yielding higher OPV efficiencies than P3HT [37–39]. The realization that morphology and device efficiency are
intimately related resulted in rapid advances in the use of new instrumentation to
study organic nanostructure [40, 41]. At the same time, further OPV device
efficiency increases were realized by the use of optimized morphology-controlling
strategies including the use of thermal annealing [42], solvent annealing [43], and
the application of various co-solvent additives [44, 45]. The most cited paper in all
of OPV research (>2,900 total) was published by Li et al. [43]. It demonstrated the
change in morphology associated with thermal and solvent annealing and was the
first published and certified efficiency record of over 4% for an OPV device.
Figure 3 shows J/V curves of P3HT:PCBM OPV devices from this seminal paper.
In the same month, two other groups also published >4% efficiency with P3HT:
PCBM but with different composition ratio, layer thickness, and annealing treatment [42, 46]. Although the OPV field has expanded widely beyond the P3HT:
PCBM system, P3HT:PCBM remains the “fruit fly” of OPV because the materials
are widely available with sufficient purity, and because all manner of new
processing techniques can be tested with the knowledge that small changes to the
microstructure yield large changes in OPV device PCE.
To demonstrate the pervasive study of P3HT as a model polymer for OPV, we
tracked the number of articles published about P3HT and OPV. In Fig. 1 we show
the number of scientific papers (as counted by Web of Knowledge) published per
year under the search terms “organic photovoltaic”, “P3HT”, and “organic
photovoltaic + P3HT”. This search shows that in 2013, more than 300 out of almost
1,700 OPV papers were searchable with P3HT as the OPV polymer, although P3HT
has not been a record polymer since 2006. Many of the other more than 500 P3HT
articles involve microstructural or photophysical studies that inform the OPV field.
188
A.J. Moule ´ et al.