ABSTRACT
Organic photovoltaics (OPVs) have for small-scale devices (<1 cm2) now reached levels with respect to both efficiency and stability where they will soon be able to compete with amorphous silicon solar cells pending continued development at the current rate. With reported efficiencies up to 9-10% [25,38] and with numerous reports on improved outdoor stabilities [21,27,54,63], the field has reached the point where it is essential that more effort is allocated toward the original idea behind OPVs, which is high-throughput production of inexpensive organic solar cells on flexible substrates-preferably using roll-to-roll (R2R) processing. Today, most research is performed through preparation of small-scale devices on rigid substrates, and although the transfer to larger areas and flexible substrates might seem straightforward, this is definitely not the case. Many of the
processing techniques used in the laboratory do not comply with high-throughput production. Take as an example spin coating. This is by far the most common way of applying the different thin layers in organic solar cells, but the technique does not scale well to larger areas, is not R2R compatible, and far too much material is wasted in the process. The use of vacuum-deposited electrodes is another problem, as high vacuum requires extra energy and compromises throughput, which consequently brings up the cost of the final device. Alternative ways such as printable electrodes must be sought. As silver is presently the only real candidate for printing, the geometry of the device has to have an “inverted” structure, thus changing the buildup of the more commonly used “normal” geometry.
