Influence of the Ethylhexyl Side-Chain Content on the Open-Circuit Voltage in rr-Poly(3-hexylthiophene-co-3-(2-ethylhexyl)thiophene) Copolymers
Influence of the Ethylhexyl Side-Chain Content on the Open-Circuit Voltage in rr-Poly(3-hexylthiophene-co-3-(2-ethylhexyl)thiophene) Copolymers
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DOI：
10.1021/ma300263a
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发表时间：
2012-05-08
期刊：
影响因子：
5.5
通讯作者：
Thompson, Barry C.
中科院分区：
文献类型：
--
作者：
Burkhart, Beate;Khlyabich, Petr P.;Thompson, Barry C.
虽然最近已经相当多的关注聚合物烷基侧链对共轭聚合物的影响：富勒烯太阳能电池的性能，特别是V-oc和J（sc），侧链的定位，长度和分支的效果的清晰和全面的图片还没有发展。为了解决这些问题，我们设计了一个简单的和模块化的无规共聚物模型系统的基础上rr-P3 HT。研究了r-聚（3-己基噻吩-co-3-（2-乙基己基）噻吩）共聚物中支化2-乙基己基侧链（10%、25%和50%）的量的增加对诸如紫外-可见吸收、聚合物结晶度、HOMO能级、聚合物：PC 61 BM太阳能电池性能以及特别是V-oc的性质的影响，并且与相应的均聚物P3 HT和聚（3-（2-乙基己基）噻吩）（P3 EHT）进行了比较。具有50%或更少2-乙基己基侧链的聚合物（P3 HT（90）-共-EHT 10、P3 HT（75）-共-EHT 25、P3 HT（50）-共-EHT 50）具有相同的带隙和相似的吸收性质，并且还保留P3 HT的半结晶性质，而P3 EHT具有更高的带隙和更低的吸收系数。通过电化学在溶液和薄膜中测定聚合物HOMO水平，并且对于溶液中的所有聚合物几乎是相同的，而在固态下，2-乙基己基侧链的量的增加导致HOMO水平的显著和相关的降低。这种降低直接反映在聚合物：PC61 BM太阳能电池中测量的V-oc中，其随着2-乙基己基侧链含量的增加而增加，表明对于该聚合物家族，V-oc的HOMODONOR-LUMOACCEPTOR依赖性相对直接。P3 HT（75）-共-EHT 25受益于增加的V-oc（0.69V）、与P3 HT相同数量级的J（sc）（9.85mA/cm（2））和高FF，并最终实现3.85%的效率，超过P3 HT的测量效率（V-oc = 0.60V，J（sc）= 9.67mA/cm（2），效率= 3.48%）。观察到的效率增加表明，支链烷基侧链的无规掺入也可以成功地用于其他聚合物中，以最大化V-oc，同时保持带隙并改善整体聚合物：富勒烯太阳能电池性能。
Although recently considerable attention has been paid to the impact of polymer alkyl side chains on conjugated-polymer:fullerene solar cell performance, and especially the V-oc and J(sc), a clear and comprehensive picture of the effect of side-chain positioning, length, and branching has yet to evolve. In order to address some of these questions, we designed a simple and modular model system of random copolymers based on rr-P3HT. The influence of increasing amounts of branched 2-ethylhexyl side chains (10, 25, and 50%) in rr-poly(3-hexylthiophene-co-3-(2-ethylhexyl)thiophene) copolymers on properties such as UV-vis absorption, polymer crystallinity, HOMO energy levels, polymer:PC61BM solar cell performance, and especially the V-oc was studied and compared to the corresponding homopolymers P3HT and poly(3-(2-ethylhexyl)thiophene) (P3EHT). Polymers with 50% or less 2-ethylhexyl side chains (P3HT(90)-co-EHT10, P3HT(75)-co-EHT25, P3HT(50)-co-EHT50) have the same band gap and similar absorption properties and also retain the semicrystalline nature of P3HT, whereas P3EHT has a higher band gap and lower absorption coefficient. Polymer HOMO levels were determined by electrochemistry in solution and thin film and are virtually identical for all polymers in solution, whereas in the solid state an increase in the amount of 2-ethylhexyl side chains leads to marked and correlated decrease in the HOMO levels. This decrease is directly reflected in the V-oc measured in polymer:PC61BM solar cells which increases with increasing 2-ethylhexyl side-chain content, indicating a relatively straightforward HOMODONOR-LUMOACCEPTOR dependence of the V-oc for this family of polymers. P3HT(75)-co-EHT25 benefits from an increased V-oc (0.69 V), a J(sc) (9.85 mA/cm(2)) on the same order of P3HT, and a high FF and ultimately achieves an efficiency of 3.85% exceeding that measured for P3HT (V-oc = 0.60 V, J(sc) = 9.67 mA/cm(2), efficiency = 3.48%). The observed efficiency increase suggests that the random incorporation of branched alkyl side chains could also be successfully used in other polymers to maximize the V-oc while maintaining the band gap and improve the overall polymer:fullerene solar cell performance.