Evaluation of flexible organic and hybrid perovskite photovoltaic device stability

Toshiyuki Urano^a

^aChemical materials evaluation and reserch base

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Toshiyuki Urano, 010
Publication date: 5th February 2015

The Chemical Materials Evaluation and Research Base (CEREBA) was founded in 2011 as a common research and development (R&D) base for the Japanese chemical industry, with the purpose of accelerating the commercialization of new chemical materials for use in organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs). Also, since October 2013, CEREBA has conducted additional projects aimed at developing materials and evaluation methods for perovskite (PVK) hybrid photovoltaic devices. We have achieved light-soaking stability of over 500 h for PVK solar cells fabricated on glass substrates, with a power conversion efficiency (PCE) of 13%. However, to develop PVK solar cells on flexible substrates, the correlations between their stabilities and water vapor or oxygen transmission rates (WVTR and OTR, respectively) are of considerable importance and require detailed study. In this report, we present our examination of WVTR evaluation methods for the characterization of barrier layers in flexible devices. The difficulty in reliably evaluating WVTR below 10-3 g/m2/day is a well-known problem, because different measurement methods [1, 2] yield different WVTR values, with discrepancies greater than one order of magnitude. We have developed two approaches to eliminating these discrepancies: (1) Heat treatment at 70 ℃ for 24 h prior to WVTR measurement and (2) usage of reference films with small orifices composed of aluminum foil attached to a 100-μm-thick PET film, with an orifice opening area (S) of 10-8  10-4 m2 corresponding to a WVTR of 10-5  10-1 g/m2/day. We have obtained a good linear relationship between WVTR and S, even in cases involving different evaluation methods such as atmospheric pressure ionization mass spectrometry (API-MS), cavity ring-down spectroscopy (CRDS), and a differential pressure system (DELTAPERM). As a result, we have successfully identified correlations between different methods and determined appropriate measurement conditions for the reliable evaluation of WVTR. We have also used this procedure to properly evaluate barrier-layer properties in OPV and PVK flexible devices, and have obtained identical WVTR values with an error of within 20% using the three different methods mentioned above. This is a remarkable achievement toward the standardized characterization of barrier layers in flexible devices. In conclusion, we have successfully developed an original approach to the reliable evaluation of WVTR, which is accurate down to the 10-5 g/m2/day level, and applied it to the study of correlations between the WVTR and stabilities of flexible OPV and PVK devices. In the next research stage, we plan to apply the OTR evaluation methods we previously developed for use in our OLED R2R process, in order to evaluate the stability dependence of OPV and PVK devices on the barrier layer OTR properties.

[1] Burrows, P.E.; Graff, G.L.; Gross, M.E.; Martin, P.M.; Shi, M.K.; Hall, M.; Mast, E.; Bonham, C.; Bennett, W.; Sullivan, M.B.“Ultra barrier flexible substrates for flat panel　displays," Displays 2001, 22, 65-69. [2] Hara, S.; Suzuki, A.; Takahagi H. “Challenges toward　reliable evaluation of high water barrier property,” Proc. of the International Display Workshop 2013 2013.

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