1 Scientific RepoRts | 7: 1305 | DOI:10.1038/s41598-017-01505-w www.nature.com/scientificreports Comparative indoor and outdoor stability measurements of polymer based solar cells Yiwei Zhang 1 , Hunan Yi 2 , Ahmed Iraqi 2 , James Kingsley 3 , Alastair Buckley 1 , tao Wang 4 & David G. Lidzey 1 We report comparative indoor and outdoor stability testing of organic solar cells based on a blend between a donor-acceptor polyfuorene copolymer and a fullerene derivative. The outdoor testing was conducted for a period over 12,000 hours in Shefeld, England, with a Ts80 lifetime determined in excess of 10,000 hours (420 days). Indoor lifetime testing was performed on solar cells using a solar simulator under a constant irradiance of 1000 W/m 2 for more than 650 hours. We show that under the conditions explored here, device degradation under the two sets of conditions is approximately dependent on the absorbed optical energy dose. Organic semiconductors are being explored for applications as the active layer in solar cell devices 1–3 . Recent years have seen a growth in device power conversion efciency (PCE), with efciency values reported in excess of 10% 4–8 for fullerene-containing organic photovoltaics (OPVs) and 12% for non-fullerene OPVs 9 . Such progress has come as a result of the design and synthesis of new materials together with the development of optimised material fabrication techniques. However, the achievement of high PCE is not the only impediment for the prac- tical application of organic photovoltaic (OPV) devices, rather it is additionally necessary to reduce materials and manufacturing costs and extend operational lifetime. In recent years, a number of innovative fabrication techniques have been developed that are compatible with high volume, low-cost manufacture processes 10–13 . As a result of this, increased attention is now being paid to improving the operational stability of OPV devices 14–19 . Te operational lifetime of thin-flm photovoltatic devices can be characterised by two diferent lifetimes, namely the T80 and Ts80 lifetime 20 . Here, the T80 lifetime is simply the time over which the device PCE reduces to 80% of its initial value. OPV devices however ofen undergo an initial period of relatively rapid reduction in their efciency; a process known as ‘burn-in’. Following this, the reduction in efciency then stabilises and drops at a slower, more linear rate. Te exact identifcation of the end of burn-in period is not straight forward, but can ofen be identifed by the onset of the period of linear reduction in device PCE. On identifcation of the end of burn-in, a second lifetime parameter can then be determined; namely the Ts80 lifetime. Tis is the time required for the device PCE to fall by 80% of its value defned at the end of burn-in. Te reduction in operational efciency of OPVs over a range of time-scales (including burn-in) has been attributed to a combination of factors that can be initiated by the ingress of oxygen and water. Tese include oxidation or damage to device electrodes and oxidation of both donor and acceptor materials. Te ingress of water can also induce aggregation of fullerenes or generate an insulating metal oxide interlayer at the interface between the active layer and the electrode that impedes charge extraction. Te exposure of the active layer can also generate photo-oxidation reactions that either result in the formation of sub-gap states that cause additional recombination or reduce charge carrier mobility. Degradation can also result from thermal efects that drive mor- phological changes in polymer organization (disruption of π–π stacking) 21 , or induce aggregation or crystalliza- tion of the fullerene, limiting the OPV’s ability to successfully dissociate excitons. For a comprehensive discussion on degradation mechanisms that operate in OPV devices, we direct readers to a recent review 22 . Extrapolated OPV Ts80 lifetimes in excess of 6.2 years have now been determined on the basis of indoor meas- urements performed using a solar simulator 23 . However it is necessary to explore device stability when used in outdoor conditions as laboratory-based accelerated lifetime tests rarely fully replicate all degradation processes to which a device operating under real-world conditions may experience. A number of recent outdoor experiments 1 Department of Physics and Astronomy, University of Shefeld, Shefeld, S3 7RH, UK. 2 Department of chemistry, University of Sheffield, Sheffield, S3 7HF, UK. 3 Ossila Ltd, Kroto Innovation Centre, Broad Lane, Sheffield, S3 7HQ, UK. 4 School of Materials Science and Engineering, Wuhan University of Technology, Wuhan, 430070, China. Correspondence and requests for materials should be addressed to D.G.L. (email: d.g.lidzey@shefeld.ac.uk) Received: 27 January 2017 Accepted: 29 March 2017 Published: xx xx xxxx OPEN