Solution-processed organic photovoltaic devices of non-fullerene electron

When?

Thursday 4 October 2012, 13.00 to 14.00

Where?

ATI seminar room - 02ATI02

Open to:

Staff, Students

Speaker:

Dr Panagiotis E. Keivanidis Centre for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia

Bulk heterojunctions (BHJ) of fullerene-based acceptors blended with polymeric donors have attracted considerable attention as functional layers for flexible, lightweight, and low-cost photovoltaic devices that may serve as power sources for portable electronic products. Reported power conversion efficiencies (PCEs) of polymer/fullerene OPV devices are approaching the value of 10% [1] that is considered necessary for the successful commercialization the third generation of photovoltaics.

There is ongoing development of alternative n-type materials to substitute the commonly used fullerene-type acceptors in OPV devices [2]. One interesting class of these materials is the class of perylene diimide (PDI) derivatives. PDIs not only exhibit strong absorption at long wavelengths
and favourable charge transport properties but they also can be combined with block copolymer macromolecular architectures for achieving predictable tuning of the device photoactive layer microstructure [3]. Steady improvement in the PCE values of organic solar cells based on PDI derivatives has led to PCE values of >2.5% [4].

The impact of active layer microstructure on the mechanism of charge photogeneration in PDI based OPV blends remains less clear than in the case of fullerene-based systems. This is due in part to the fact that fullerenes are pseudospherical geometrical objects, whereas PDI molecules are rigid
planar structures that tend to form aggregates which can readily support the formation of intermolecular excited states, also termed excimers.

In this seminar I will present an overview of research results collected for OPV devices of fluorine copolymers blended with the ethylpropyl-substituted PDI derivative (PDI-EP). Based on data of electro-optical, thermal, and morphology characterization experiments a discussion will be made on the factors that limit the device efficiency in these PDI systems [5]. Finally recent results will be presented for a new organic composite of a low band gap polymer blended with PDI-EP that exhibits a PCE value of 1.37% ± 0.06 % for device geometries that are currently under optimization.

References
[1] M. A. Green, K. Emery, et al., Prog. Photovoltaics Res. Appl. 2011, 19, 84
[2] P. Sonar, J. P. F. Lim, et al., Energy Environ. Sci., 2011, 4, 1558; Y. Lin , Y. Li, X. Zhan, Chem. Soc. Rev. 2012, 41, 4245
[3] S. Huettner, J. M. Hodgkiss, et al., J. Phys. Chem. B, 2012 116, 10070
[4] G. D. Sharma, P. Balraju, et al., Sol. Energy Mater. Sol. Cells 2009 93, 2025; S. Rajaram, R.Shivanna, et al., J. Phys. Chem. Lett. 2012, 3, 2405
[5] P. E. Keivanidis, I. A. Howard, et al., Adv. Funct. Mater. 2008, 18, 3189; I. A. Howard, F. Laquai, et al., J. Phys. Chem. C 2009, 113, 21225; P. E. Keivanidis, P. H. H. Ho, et al., Adv. Funct. Mater. 2010, 20, 3895; P. E. Keivanidis, V. Kamm V., et al., Adv. Mater. 2010, 22, 5183l; P. E. Keivanidis, F. Laquai, et al., Adv. Funct. Mater. 2011, 21, 1355