Sensitizer Effects on the Transport Properties of Polymer:Sensitizer Organic Blend
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1270-II09-19
Sensitizer Effects on the Transport Properties of Polymer:Sensitizer Organic Blend Karina Aleman1, Svetlana Mansurova1, Andrey Kosarev1, Ponciano Rodriguez1, Klaus Meerholz2 and Sebastian Koeber2 1
National Institute for Astrophysics, Optics and Electronics, AP 51 y 216, Puebla, 72000, Mexico 2 University of Cologne, Insitute of Physical Chemistry, Luxemburger Str. 116, Cologne, D-50939, Germany ABSTRACT In this work we studied the effect of sensitizer concentration on a mobilitylifetime product µτ , on photoconductivity response time τ ph , and on drift mobility µ of the majority carriers in an organic polymer:sensitizer blend. The intensity modulated photocurrent and photo-EMF technique were used as experimental tools for this purpose. The studied material consists of a mixture of the novel non-conjugated main chain hole-transporting polymer PFO6:PDA (Poly(N,N’-bis(4-hexyloxyphenyl)-N’-(4(9-phenyl-9H-fluoren-9-yl)phenyl)phenylen-1,4- diamine) sensitized with the highly soluble C60 derivative PCBM (phenyl-C61-butyric acid methyl ester) in the range from Ζ = 1 to 40 wt.-%. It was experimentally observed that (1) at the increasing sensitizer concentration the overall photoconductivity increases; (2) the majority carrier type switches from holes to electrons at approximately 2:1 polymer:sensitizer ratio; (3) the holes response time becomes shorter at the decreasing polymer fraction, while the electrons lifetime is only slightly dependent on sensitizer concentration; (4) the hole mobility-lifetime product decreases at the decreasing concentration of hole transporting component (polymer), while the electrons mobility-lifetime product increases at the increasing concentration of the electron transporting component (sensitizer); (5) the same is true for the carriers mobilities. INTRODUCTION Due to their promising properties such as flexibility, possibility to use printing process in roll to roll and low cost, organic solar cells have attracted a lot of attention during the last decade. Bulk heterojunction (BHJ) solar cells based on blends of donor (photoconductive polymer) and acceptor (small molecule sensitizer) belong to the most promising candidates for this application, as efficiencies in the range of 5% have been achieved recently [1] in poly(3-hexyl thiophene-2,5-diyl) (P3HT):(6,6)-phenyl-butyric acid methyl ester (PCBM) blend devices. Transport properties of the active material are the crucial factors determining the performance of organic solar cells [2, 3]. However, as the blend of two different material types cannot be described by a simple superposition of the single material properties, a prediction of the bipolar charge transport in a solar cell is not straightforward. In this context, the experimental data on donor/acceptor ratio dependent transport characteristics would have been of particular interest and a considerable amount of work has been devoted recently to this problem [4-7]. The experimental methods used to obtain information about charge transport in organic semiconductors – time-of
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