Elsevier

Organic Electronics

Volume 19, April 2015, Pages 34-60
Organic Electronics

Review
Solution-processable polymeric solar cells: A review on materials, strategies and cell architectures to overcome 10%

https://doi.org/10.1016/j.orgel.2015.01.014Get rights and content

Highlights

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    Organic photovoltaics will become 30 years old relatively soon.

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    Highest PCE already reach 10.1% and 11.8% for single and tandem configuration.

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    The most efficient polymeric donors and acceptors are in detail reviewed.

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    Fabrication/processing procedures also contribute to increase efficiency.

Abstract

Organic photovoltaics will become 30 years old relatively soon. In spite of the impressive development achieved throughout these years, especially in terms of reported power conversion efficiencies, there are still important technological and fundamental obstacles to circumvent before they can be implemented into reliable and long-lasting applications. Regarding device processing, the synthesis of highly soluble polymeric semiconductors first, and fullerene derivatives then, was initially considered as an important breakthrough that would definitely change the fabrication of photovoltaics once for all. Nowadays, the promise of printing solar cells by low-cost and high throughput mass production techniques still stands. However, the potential and the expectation raised by this technology is such that it is considerably difficult to keep track of the most significant progresses being now published in different and even monographic journals. There is therefore the need to compile the most remarkable advances in well-documented reviews than can be used as a reference for future ideas and works. In this letter, we review the development of polymeric solar cells from its origin to the most efficient devices published to date. After analyzing their fundamental limits, we separate these achievements into three different categories traditionally followed by the scientific community to push devices over 10% power conversion efficiency: Active materials, strategies -fabrication/processing procedures- that can mainly modify the active film morphology and result in improved efficiencies for the same starting materials, and all the different cell layout/architectures that have been used in order to extract as high photocurrent as possible from the Sun. The synthesis of new donors and acceptors, the use of additives and post-processing techniques, buffer interlayers, inverted and tandem designs are some of the most important aspects that are in detailed reviewed in this letter. All have equally contributed to develop this technology and leave it at doors of commercialization.

Section snippets

Broader context

Organic photovoltaics (OPV) was born as a new possibility to decrease the fabrication cost of solar devices and be validated as one of the most promising renewable energy sources. Thirty years later they have still however not fulfilled this expectative. The non-stop development of existing technologies makes it still difficult for OPV to compete with traditional systems such as silicon solar cells in terms of efficiency and reliability. However, the unique selling properties of this technology

Materials

During the 80s the use of organic materials for photovoltaic devices resulted in very low efficiencies, typically below 0.1%. It was not until 1986 when Tang reported the first organic solar cell with an efficiency of 1% thanks to the combination of a donor and acceptor material [21]. Later on, the exciton dissociation rate was enhanced with the discovery by Sariciftci et␣al. of the charge transfer phenomenon from the MEH-PPV polymer to a highly electron accepting molecule, namely

Strategies: Fabrication/processing procedures

The morphology of the film in BHJ solar cells is a critical parameter to control the exciton dissociation rate, optimize charge transport, minimize bulk recombination, maximize the photocurrent and hence enhance the efficiency of the device [96]. On the one hand, a large amount of donor/acceptor interfaces is required in order to dissociate a large number of photogenerated excitons. On the other hand, the domain size of each material phase and interconnection between them is also important for

Device layout/architectures

All the layers that form an organic solar cell have a direct influence in the performance of the device. Buffer interlayers are of crucial interest in order to increase the efficiency of devices. The use of interfacial materials dates back from the very beginning of the OLED development when PEDOT:PSS, calcium (Ca), and LiF were initially used with the objective of modifying and improving the charge injection properties from the purely metallic electrodes to the emitting semiconductor [117],

Summary

In this letter, we have initially presented the fundamental limits of polymeric solar cells, the factors that limit their performance and the different possible approaches to maximize it. We have then offered a comprehensive and detailed review of the most efficient attempts to overcome the long ambitioned 10% PCE in polymeric devices. We have divided the development of polymeric solar cells in three categories indicating the most efficient attempt for every case (Table␣8):

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    Materials:

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      10% PCE

Acknowledgements

We thank the European Community’s Seventh Framework Programme (FP72007-2013) under Grants Nos. 287818 and 604397 of the X10D and ARTESUN projects respectively for providing financial support.

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