On the Effect of Prevalent Carbazole Homocoupling Defects on the Photovoltaic Performance of PCDTBT:PC71BM Solar Cells
On the Effect of Prevalent Carbazole Homocoupling Defects on the Photovoltaic Performance of PCDTBT:PC71BM Solar Cells
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DOI：
10.1002/aenm.201601232
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发表时间：
2016-11-01
影响因子：
27.8
通讯作者：
Sommer, Michael
中科院分区：
文献类型：
--
作者：
Lombeck, Florian;Komber, Hartmut;Sommer, Michael
研究了经典供体-受体共聚物PCDTBT（聚（N-9-十七基-2,7-咔唑-alt -5,5-（4,7-二-2-噻吩基-2,1,3-苯并噻二唑）））与无意形成的主链缺陷相关的光物理性质和太阳能电池性能。在各种 Suzuki 缩聚条件下制备的 PCDTBT 中发现了大量咔唑-咔唑均聚物 (Cbz hc)。 Cbz hc 根据所使用的合成方案在 0 至 8 mol% 之间变化，并通过详细的核磁共振光谱（包括模型化合物）进行量化，从而可以根据光谱建立校准曲线。这些结果得到了对规则交替链和同偶链的结构、电子和光学性质的扩展时间依赖性密度泛函理论研究的证实。 PCDTBT:富勒烯共混物太阳能电池的光伏特性显着取决于恒定分子量下的Cbz hc含量，其中Cbz hc含量的增加导致短路电流J(SC)大幅降低。随着 Cbz hc 含量的增加，J(SC) 的下降幅度大于低能量吸收带的强度，这表明吸收的小损失不能单独解释 J(SC) 的下降，而是 TBT 单元上更局部的 LUMO 能级和高度缺陷样品中发现的较低空穴迁移率的综合影响。具有优化分子量的无同偶联 PCDTBT 无需进行大量优化即可实现高达 7.2% 的最高效率。
The photophysical properties and solar cell performance of the classical donor-acceptor copolymer PCDTBT(poly(N-9-heptadecanyl-2,7-carbazole-alt -5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole))) in relation to unintentionally formed main chain defects are investigated. Carbazole-carbazole homocouplings (Cbz hc) are found to significant extent in PCDTBT made with a variety of Suzuki polycondensation conditions. Cbz hc vary between 0 and 8 mol% depending on the synthetic protocol used, and are quantified by detailed nuclear magnetic resonance spectroscopy including model compounds, which allows to establish a calibration curve from optical spectroscopy. The results are corroborated by extended time-dependent density functional theory investigations on the structural, electronic, and optical properties of regularly alternating and homocoupled chains. The photovoltaic properties of PCDTBT:fullerene blend solar cells significantly depend on the Cbz hc content for constant molecular weight, whereby an increasing amount of Cbz hc leads to strongly decreased short circuit currents J(SC). With increasing Cbz hc content, J(SC) decreases more strongly than the intensity of the low energy absorption band, suggesting that small losses in absorption cannot explain the decrease in J(SC) alone, rather than combined effects of a more localized LUMO level on the TBT unit and lower hole mobilities found in highly defective samples. Homocoupling-free PCDTBT with optimized molecular weight yields the highest efficiency up to 7.2% without extensive optimization.