Though the first reports addressing the photovoltaic potential of organic molecules date back to the 1970s, the field of organic solar cells (OSCs) has really emerged over the last two decades. Since the start of the new millennium, the number of published OSC papers has taken off, showing an average growth of ∼65% per year, almost twice the breathtaking pace of evolution of the world photovoltaic market [1].
This trend suggests that a large number of laboratories have recently entered this field. Since OSCs are located at the crossover of several areas, scientists with different backgrounds are working on this topic. In essence, this should be a good thing. Increasing the number of people focused on this tremendous renewable will hopefully help solve the planet's energy needs. Although they are potentially cheap, easy to fabricate, and energy effective, OSCs still show lower efficiency and lifetimes compared with their inorganic counterparts. In this respect, the OSC field does indeed need the greatest manpower possible to tackle its limitations quickly.
Unfortunately, the OSC community currently suffers from its own success. The very large choice of publishing options offered to authors and the increasing difficulty in gaining impact within the community, combined with a lack of accuracy in measuring, reporting, and reviewing, has seen a significant number of papers claiming unrealistic and scientifically questionable OSC properties and performances. ‘World record’ OSC efficiencies are popping up almost every month, leading the community into an endless and dangerous tendency to outbid the last report. Such phases of disharmony are not unusual in a young scientific field. But it is important to keep them short and not let them create skepticism or mistrust of the field itself.
Accurately measuring the efficiency of OSCs under simulated sunlight (air mass 1.5) [2] is a process that has to be carried out according to a specific protocol [3] and [4]. Measurements should be performed on cells having a reasonable active surface area in order to reduce the influence of potential artifacts. For the sake of accuracy, researchers should always be encouraged to seek independent confirmation of results. This can be done, for example, at national institutes that deliver certificates like the Fraunhofer Institute for Solar Energy Systems (ISE) in Germany, the US National Renewable Energy Laboratory (NREL), or the Japanese National Institute of Advanced Industrial Science and Technology (AIST). In order to provide an authoritative and reliable picture of the state of the art, Martin A. Green et al. have published an extensive six-monthly listing of the highest independently confirmed efficiencies of all types of solar cells and modules since 1993 in Progress in Photovoltaics [5].
Although official certificates would seem necessary for claims of world record efficiencies, all actors in the field would agree that there is also a strong need to report device performances without independent verification. The objectivity of this approach relies entirely on basic ethical rules that should lead authors to regularly question their findings and constantly push the accuracy of their measurements to the highest possible level. But responsibility also lies with editors, who should ensure a thorough reviewing process, even if the cost is a slight delay in the publication procedure or a reduced number of papers published. This is especially necessary in the case of world record efficiencies for which the highest level of scientific evaluation is required to avoid falling for the easy attraction of a newsworthy publication. This has not always been the case in the recent past.
The current outbidding phenomenon does a severe disservice to the whole OSC community, damaging its reputation. Solar cells and especially OSCs face enough difficulties in convincing people of their benefit over other energy sources. We should all act together for their success, not against it.
Signed by T. Ameri*, P. Denk*, H.-J. Egelhaaf*, K. Forberich*, M. Koppe*, M. Morana*, M. C. Scharber*, C. Waldauf*, Konarka Austria GmbH, Austria; B. de Boer, University of Groningen, The Netherlands; K. Emery, G. Rumbles, National Renewable Energy Laboratory, USA; J. M. Kroon, Solar Energy – Energy Research Center of the Netherlands, The Netherlands; G. G. Malliaras, Cornell University, USA; M. D. McGehee, Stanford University, USA; J. Nelson, Imperial College, London, UK; M. Niggemann, Fraunhofer Institute for Solar Energy Systems, Germany; M. Pfeiffer, Heliatek GmbH, Germany; M. K. Riede, Institut für Angewandte Photophysik, Germany; S. E. Shaheen, University of Colorado, Denver, USA; M. Wienk, University of Technology, Eindhoven, The Netherlands.
Further reading
[1] A. Jäger-Waldau, PV Status Report 2006 Office for Official Publications of the European Communities, Luxembourg (2006)
[2] American Society for Testing and Materials (ASTM) Standard G159, West Conshoken, PA, USA
[3] K. Emery, C. Osterwald, Current Topics in Photovoltaics, 3 Academic Press, London, UK (1988)
[4] V. Shrotriya et al. Adv. Funct. Mater., 16 (2006), p. 2016
[5] M.A. Green et al. Prog. Photovolt: Res. Appl., 15 (2007), p. 425
*The opinions expressed in this article are solely those of the author and signatories, and do not represent those of Konarka Austria GmbH.