Electron Collection as a Limit to Polymer:PCBM Solar Cell Efficiency: Effect of Blend Microstructure on Carrier Mobility and Device Performance in PTB7:PCBM
Electron Collection as a Limit to Polymer:PCBM Solar Cell Efficiency: Effect of Blend Microstructure on Carrier Mobility and Device Performance in PTB7:PCBM
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DOI：
10.1002/aenm.201400311
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发表时间：
2014-10-07
影响因子：
27.8
通讯作者：
Nelson, Jenny
中科院分区：
文献类型：
--
作者：
Foster, Samuel;Deledalle, Florent;Nelson, Jenny
利用空间电荷限制电流迁移率和光伏器件测量研究了聚[4，8-双[（2-乙基己基）氧基]苯并[1，2-B：4，5-b ']二噻吩-2，6-二基][3-氟-2-[（2-乙基己基）羰基]噻吩并[3，4-B]噻吩二基]（PTB 7）和[6，6]-苯基-C61-丁酸（PCBM）的现有技术共混物在大活性层厚度下的不良光伏性能。发现性能差是由于电子迁移率相对较低。这归因于PTB 7聚集的倾向较低，这降低了富勒烯形成连接网络的能力。将PCBM含量增加60-80重量%会增加电子迁移率，并相应地改善较厚器件的性能，导致在300 nm处的填充因子（FF）接近0.6。结果证实，通过仅改善富勒烯相的连接性，有效的电子和空穴收集对于300 nm厚的PTB 7：PCBM器件是可能的。此外，它表明，溶剂添加剂1，8-二碘辛烷（DIO），用于最高效率的PTB 7：PCBM设备，不改善的厚度依赖性，因此，不会导致增加空穴或电子迁移率或载流子寿命。因此，研究人员面临的一个关键挑战是开发新的方法来确保共混物中富勒烯相的连通性，而不依赖于大量过量的富勒烯或聚合物的强烈聚集。
The poor photovoltaic performance of state-of-the-art blends of poly[4,8-bis[(2-ethylhexyl) oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl] (PTB7) and [6,6]-phenyl-C61-butyric acid (PCBM) at large active layer thicknesses is studied using space-charge-limited current mobility and photovoltaic device measurements. The poor performance is found to result from relatively low electron mobility. This is attributed to the low tendency of PTB7 to aggregate, which reduces the ability of the fullerene to form a connected network. Increasing the PCBM content 60-80 wt% increases electron mobility and accordingly improves performance for thicker devices, resulting in a fill factor (FF) close to 0.6 at 300 nm. The result confirms that by improving only the connectivity of the fullerene phase, efficient electron and hole collection is possible for 300 nm-thick PTB7:PCBM devices. Furthermore, it is shown that solvent additive 1,8-diiodooctane (DIO), used in the highest efficiency PTB7:PCBM devices, does not improve the thickness dependence and, accordingly, does not lead to an increase in either hole or electron mobility or in the carrier lifetime. A key challenge for researchers is therefore to develop new methods to ensure connectivity in the fullerene phase in blends without relying on either a large excess of fullerene or strong aggregation of the polymer.