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Radical Salt-Doped Hole Transporters in Organic Photovoltaic Devices

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journal contribution
posted on 07.08.2007 by SanthiSagar Vaddiraju, Mathew Mathai, Emmanuel Kymakis, Fotios Papadimitrakopoulos
Efficient photovoltaic devices were demonstrated from thick polymer films (2500 Å), using ternary mixtures of C60, a polycarbonate linked TPD (N,N,N‘,N‘-tetrakis(phenyl)benzidine)) polymer (PTPD), and a small molecular weight radical salt of a TPD derivative, in an indium tin oxide/blend/Al configuration. The binary PTPD mixtures with salt and C60 were also investigated in a similar device configuration. The addition of the radical salt increases the hole conductivity of the PTPD host matrix and subsequently enhances the photocurrent by 1 order of magnitude. On the other hand, blending PTPD with C60 increases the photocurrent by 3 orders of magnitude to produce a short circuit current (Isc) of 0.22 mA/cm2. The incorporation of these two binary systems into a ternary blend shows a further increase in the Isc (0.33 mA/cm2) with a power conversion efficiency of 0.47%. To the best of our knowledge this is the first time that a radical salt has been used in an organic photovoltaic device configuration. This study provides insight on the interplay of the three components of this ternary system to both open circuit voltage (Voc) and Isc. Further optimization in structure and morphology of these devices can lead to significant performance enhancement.