Fluorinated Copolymer PCPDTBT with Enhanced Open-Circuit Voltage and Reduced Recombination for Highly Efficient Polymer Solar Cells,Journal of the American Chemical Society

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Fluorinated Copolymer PCPDTBT with Enhanced Open-Circuit Voltage and Reduced Recombination for Highly Efficient Polymer Solar Cells
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2012-08-29 , DOI: 10.1021/ja305039j
Steve Albrecht ₁ , Silvia Janietz ₂ , Wolfram Schindler ₃ , Johannes Frisch ₄ , Jona Kurpiers ₁ , Juliane Kniepert ₁ , Sahika Inal ₁ , Patrick Pingel ₁ , Konstantinos Fostiropoulos ₃ , Norbert Koch _{3,

4} , Dieter Neher ₁

Affiliation

A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher power conversion efficiency in bulk heterojunction solar cells with PC(70)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(70)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(2), 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.

中文翻译：

用于高效聚合物太阳能电池的具有增强开路电压和减少复合的含氟共聚物 PCPDTBT

引入了一种新型氟化共聚物 (F-PCPDTBT)，与众所周知的低带隙聚合物 PCPDTBT 相比，它在具有 PC(70)BM 的本体异质结太阳能电池中表现出显着更高的功率转换效率。氟化降低了聚合物的 HOMO 能级，导致高开路电压远远超过 0.7 V。使用能量分辨透射电子显微镜进行的光谱学和形态学研究表明，氟化聚合物在原始层和混合层中聚集得更强烈，并且具有更少量的达到最佳器件性能所需的添加剂。通过线性增加电压的延时收集场和电荷提取用于深入了解氟化对自由电荷载流子生成和重组的场依赖性的影响。F-PCPDTBT 表现出明显较弱的自由电荷载流子产生的场依赖性，并且总体上有大量的自由电荷，这意味着成对重组大大减少。此外，与优化的 PCPDTBT 共混物相比，测量到非双生重组减少了 3 倍。由于非成对复合减少，氟化 PCPDTBT 与 PC(70)BM 的优化共混物的性能很大程度上取决于自由载流子生成的场依赖性，与包含的共混物相比，这种场依赖性要弱得多非氟化聚合物。对于这些优化的混合物，实现了 14 mA/cm(2) 的短路电流、0.74 V 的开路电压和 58% 的填充因子，提供了 6.16% 的最高能量转换效率。

更新日期：2012-08-29

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