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Fluorinated Copolymer PCPDTBT with Enhanced Open-Circuit Voltage and Reduced Recombination for Highly Efficient Polymer Solar Cells

By Steve Albrecht (1283739), Silvia Janietz (1271553), Wolfram Schindler (1283748), Johannes Frisch (1291398), Jona Kurpiers (1283757), Juliane Kniepert (1276560), Sahika Inal (1269558), Patrick Pingel (1271559), Konstantinos Fostiropoulos (1283742), Norbert Koch (168547) and Dieter Neher (1269552)

Abstract

A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher power conversion efficiency in bulk heterojunction solar cells with PC<sub>70</sub>BM compared to the well-known low-band-gap polymer PCPDTBT. Fluorination lowers the polymer HOMO level, resulting in high open-circuit voltages well exceeding 0.7 V. Optical spectroscopy and morphological studies with energy-resolved transmission electron microscopy reveal that the fluorinated polymer aggregates more strongly in pristine and blended layers, with a smaller amount of additives needed to achieve optimum device performance. Time-delayed collection field and charge extraction by linearly increasing voltage are used to gain insight into the effect of fluorination on the field dependence of free charge-carrier generation and recombination. F-PCPDTBT is shown to exhibit a significantly weaker field dependence of free charge-carrier generation combined with an overall larger amount of free charges, meaning that geminate recombination is greatly reduced. Additionally, a 3-fold reduction in non-geminate recombination is measured compared to optimized PCPDTBT blends. As a consequence of reduced non-geminate recombination, the performance of optimized blends of fluorinated PCPDTBT with PC<sub>70</sub>BM is largely determined by the field dependence of free-carrier generation, and this field dependence is considerably weaker compared to that of blends comprising the non-fluorinated polymer. For these optimized blends, a short-circuit current of 14 mA/cm<sup>2</sup>, an open-circuit voltage of 0.74 V, and a fill factor of 58% are achieved, giving a highest energy conversion efficiency of 6.16%. The superior device performance and the low band-gap render this new polymer highly promising for the construction of efficient polymer-based tandem solar cells

Topics: Medicine, Pharmacology, Biotechnology, Evolutionary Biology, Ecology, Cancer, Space Science, Biological Sciences not elsewhere classified, Chemical Sciences not elsewhere classified, Physical Sciences not elsewhere classified, voltage, charge, energy conversion efficiency, optimized blends, optimized PCPDTBT blends, device performance, PC 70BM, generation, power conversion efficiency, polymer HOMO level, field dependence, exhibit, Efficient Polymer Solar CellsA novel, Fluorinated Copolymer PCPDTBT, recombination
Year: 2012
DOI identifier: 10.1021/ja305039j.s001
OAI identifier: oai:figshare.com:article/2487250
Provided by: FigShare
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