title: Effect of Aging and PCBM Content on Bulk Heterojunction Organic Solar Cells Studied by Intensity Modulated Photocurrent Spectroscopy.
abstract: A series of encapsulated and nonencapsulated bulk heterojunction photovoltaic devices containing poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61butyric acid methyl ester (PCBM) with different P3HT:PCBM ratios were investigated using traditional steady-state as well as non-steady-state intensity modulated photocurrent spectroscopy (IMPS) techniques. The steady state J-V measurements showed that PCBM content did not have a significant effect on the efficiency for freshly prepared devices, whereas aged nonencapsulated devices exhibited a strong dependence on PCBM content. IMPS measurements showed a significant contribution of interfacial nongeminate recombination in nonencapsulated devices, which increased with decreasing PCBM content in the photoactive layer and cell aging. It was related to the formation of interfacial states at the P3HT/PCBM interface due to atmospheric contamination, which act as recombination centers. Device encapsulation was found to be effective in preventing the occurrence of interfacial recombination. Our results suggest that IMPS can be used as a diagnostic tool to predict the performance of bulk heterojunction organic solar cells. If a solar cell shows the presence of interfacial states as indicated by semicircle arcs in quadrant I of the IMPS complex plane plots, it is most likely that its performance will deteriorate with time due to enhanced interfacial recombination, even without further exposure to atmospheric contaminations. We conclude that interfacial nongeminate recombination is an important degradation mechanism in organic solar cells, especially in the case of exposure to atmospheric contaminants.
authors.affiliation: Department of Chemistry, The University of Western Ontario , 1151 Richmond St., London, Ontario N6A 5B7, Canada.
authors.forename: Joshua C
authors.initials: JC
authors.lastname: Byers
authors.affiliation: Institut d'Electronique du Solide et des Systèmes, Université de Strasbourg-CNRS , 23 rue du Loess, 67037 Strasbourg, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Heiser
authors.affiliation: Génie Physique, École Polytechnique de Montréal , C.P. 6079, succ. Centre-ville, Montréal, Québec H3C 3A7, Canada.
authors.forename: Maksim
authors.initials: M
authors.lastname: Skorobogatiy
authors.affiliation: Department of Chemistry, The University of Western Ontario , 1151 Richmond St., London, Ontario N6A 5B7, Canada.
authors.forename: Oleg A
authors.initials: OA
authors.lastname: Semenikhin
keywords: degradation; exciton; intensity modulated photocurrent spectroscopy (IMPS); intensity modulated photovoltage spectroscopy (IMVS); nongeminate recombination; organic photovoltaics