Charge Transport and Recombination in Low‐Bandgap Bulk Heterojunction Solar Cell using Bis‐adduct Fullerene |
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Authors: | Hamed Azimi Alessia Senes Markus C Scharber Kurt Hingerl Christoph J Brabec |
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Affiliation: | 1. Konarka Austria, Altenbergerstrasse 69, A‐4040 Linz, Austria;2. Christian Doppler Laboratory for Surface Optics, Johannes Kepler University, A‐4040 Linz, Austria;3. Friedrich‐Alexander‐University, Martensstra?e 7, 91058 Erlangen, Germany |
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Abstract: | Charge transport and recombination are studied for organic solar cells fabricated using blends of polymer poly(4,4′‐bis(2‐ethylhexyl)dithieno3,2‐b:2′,3′‐d]silole)‐2,6‐diyl‐alt‐(4,7‐bis(2‐thienyl)‐2,1,3‐benzothiadiazole)‐5,5′‐diyl] (Si‐PCPDTBT) with 6,6]‐phenyl‐C61‐butyric acid methyl ester (mono‐PCBM) and the bis‐adduct analogue of mono‐PCBM (bis‐PCBM). The photocurrent of Si‐PCPDTBT:bis‐PCBM devices shows a strong square root dependence on the effective applied voltage. From the relationship between the photocurrent and the light intensity, we found that the square‐root dependence of the photocurrent is governed by the mobility‐lifetime (μτ) product of charge carriers while space‐charge field effects are insignificant. The fill factor (FF) and short circuit current density (Jsc) of bis‐PCBM solar cells show a considerable increase with temperature as compared to mono‐PCBM solar cells. SCLC analysis of single carrier devices proofs that the mobility of both electrons and holes is significantly lowered when replacing mono‐PCBM with bis‐PCBM. The increased recombination in Si‐PCPDTBT:bis‐PCBM solar cells is therefore attributed to the low carrier mobilities, as the transient photovoltage measurements show that the carrier lifetime of devices are not significantly altered by using bis‐PCBM instead of mono‐PCBM. |
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Keywords: | bulk heterojunctions solar cells organic solar cells bis‐fullerene charge transport recombination |
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