Fluorinated Copolymer PCPDTBT with Enhanced Open-Circuit Voltage and Reduced Recombination for Highly Efficient Polymer Solar Cells
Fluorinated Copolymer PCPDTBT with Enhanced Open-Circuit Voltage and Reduced Recombination for Highly Efficient Polymer Solar Cells
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DOI：
10.1021/ja305039j
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发表时间：
2012-09-12
影响因子：
15
通讯作者：
Neher, Dieter
中科院分区：
文献类型：
--
作者：
Albrecht, Steve;Janietz, Silvia;Neher, Dieter
介绍了一种新型的含氟共聚物(F-PCPDTBT)，与众所周知的低带隙聚合物PCPDTBT相比，PC70BM在体异质结太阳电池中表现出了显著的高功率转换效率。氟化降低了聚合物的HOMO水平，导致高开路电压远远超过0.7V。光谱分析和能量分辨电子显微镜的形态研究表明，氟化聚合物在原始层和混合层中聚集得更强烈，需要的添加剂更少，才能实现最佳的器件性能。采用延时收集场和线性升压引出电荷的方法研究了氟化对自由载流子产生和复合的场依赖性的影响。研究表明，F-PCPDTBT的自由载流子产生的场依赖性显著减弱，同时自由电荷量总体较大，这意味着双态复合大大减少。此外，与优化的PCPDTBT共混物相比，非双组分复合减少了3倍。由于减少了非双组分复合，含氟PCPDTBT和PC70BM的优化共混物的性能在很大程度上取决于自由载流子产生的场依赖关系，并且这种场依赖关系比包含非氟聚合物的共混物弱得多。对于这些优化的混合物，获得了14 mA/cm(2)的短路电流，0.74V的开路电压，58%的填充系数，最高的能量转换效率为6.16%。这种新型聚合物具有优异的器件性能和较低的带隙，因此在构建高效的聚合物串联太阳能电池方面具有很高的应用前景。
A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher power conversion efficiency in bulk heterojunction solar cells with PC70BM 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 PC70BM 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.