文献翻译内量子效率为100体相异质结太阳能电池Word格式文档下载.docx

1、这种PCDTBT/PC70BM材料体相异质结电池是目前所有体相异质结太阳能电池中性能最好的，在AM1.5G、100 mW/cm-2 光照下，短路电流10.6mA cm-2, 开路电压50.88 V, 填充因子50.66 、效率56.1%。 Polymer bulk heterojunction （BHJ） solar cells based on composites of an electron-donating conjugated polymer and an electron-accepting fullerene offer promise for the realization o

2、f a low-cost, printable, portable and flexible renewable energy source14. Although BHJ solar cell performance has steadily improved, with power conversion efficiencies （PCE;he） approaching 5%, further improvements in efficiency are required for largescal ecommercialization57. 聚合物体相异质结太阳能电池是基于电荷给提共轭聚

3、合物和电荷受体富勒烯混合制作的。这种太阳能电池具有成本低、可印刷、便携和柔性等优势。尽管BHJ太阳能电池性能缓慢提高：能量转换效率接近5%，但若大规模的商业应用需要进一步提高其性能。 Rather than using a single junction architecture, the fundamental BHJ concept involves the self-assembly of nanoscale heterojunctions by spontaneous phase separation of the donor （polymer） and the acceptor （f

4、ullerene）. As a result of this spontaneous phase separation,charge-separating heterojunctions are formed throughout the bulk of the material. BHJ不是单层结构，它是通过给体（聚合物）和受体（富勒烯）自发相分离构成的纳米级别的异质结。所以自发相分离、电荷异质结分离是有机异质结材料一直讨论的。 Over the past decade, research has focused on regio-regular poly（3-hexylthiophene）

5、 （P3HT） as the standard electron-donating material in polymer BHJ solar cells, with important progress having been made in understanding the device science and the associated improvements in device efficiency. Relatively high-performance polymer BHJ solar cells made from a mixture of P3HT and 6,6-ph

6、enyl C61 butyric acid methyl ester （PCBM） have been reported, with maximum PCEs of he ?45% （refs 57）. Although approaches to improving the efficiency of P3HT/PCBM cells are still being reported, the relatively large bandgap of P3HT （_1.9 eV） limits the fraction of the solar spectrum that can be harv

7、ested, and the relatively small energy difference between the top of the p-band （highest occupied molecular orbital, HOMO） of P3HT and the lowest unoccupied molecular orbital （LUMO） of the fullerene acceptor results in a low open-circuit voltage, VOC =0.6 V.These fundamental energies defined by the

8、electronic structure of the semiconducting polymer （the energy gap and the HOMO energy） must be decreased in order achieve polymer BHJ solar cells with PCEs of 6% and higher. 在过去的十年里，P3HT作为BHJ重要的电荷给体材料，人们对其进行了大量的研究，并在理解器件工作原理方面取得重大进展，同时器件工作效率也相应的得到提高。P3HT和PCBM混合制成的BHJ太阳能电池的最高效率是4-5%。尽管有报道了提高P3HT/PCB

9、M太阳能电池性能的方法，但是P3HT相对宽的带隙（1.9ev）是限制光吸收的主要因素。P3HT的键和富勒烯受体LUMO之间较小的能量差导致了较低的开路电压：Voc=0.6v。为了使BHJ太阳能电池达到6%或者更高效率，这些通过半导体聚合物电子结构定义的基本能级必须减小。 Recently, several classes of low-bandgap polymers have been developed to better harvest the solar spectrum with deeper HOMO energies that can potentially increase V

10、OC （refs 812）.These polymers are designed to make use of internal charge transfer from an electron-rich unit to an electron-deficient moiety within the fundamental repeat unit. Among them, alternating co-polymers based on poly（2,7-carbazole） derivatives11,12, with a suite of electron-deficient moiet

11、ies to choose from, are particularly interesting（see Fig. 1）. The different electron-deficient moieties can be used to tune the electronic energy gap of the semiconducting polymer, while the deep HOMO of the carbazole leads to higher values for VOC （ref. 11）. The implied flexibility in the synthesis

12、 can lead to both a smaller bandgap that enables the harvesting of a larger fraction of the solar radiation spectrum, and a deeper HOMO energy that increases the open circuit voltage of the photovoltaic device.In their initial report of the synthesis and device performance of PCDTBT, Leclerc and col

13、leagues demonstrated a PCE of 3.6%from a BHJ cell with VOC value approaching 0.9 V.最近，有人研究出一系列的低带隙聚合物，这些聚合物具有更低的HOMO能级，能够吸收更多的光，从而提高开路电压。设计这些聚合物时可以把基本重复单元中的电荷由富电子集团转移到缺电子部分。聚合物材料合成具有灵活性，所以可以使材料具有窄带系能够吸收更多的光，还可以使HOMO能级更深以提高器件的开路电压。先前Leclerc和他的同事报道了PCDTBT的合成以及器件性能，利用PCDTBT制备的BHJ太阳能电池的效率达到3.6%，开路电压接近0.

14、9v。 We report here solar cells with 6% PCE from BHJ composites comprising PCDTBT/6,6-phenyl C71 butyric acid methyl ester（PC70BM） with short-circuit current JSC ?10.6 mA cm22, open circuit voltage VOC ?0.88 V and fill factor FF =0.66 under air mass 1.5 global （AM 1.5 G） irradiation of 100 mW cm22. T

15、he internal quantum efficiency （IQE） is close to 100%, implying that essentially every absorbed photon results in a separated pair of charge carriers and that all photogenerated carriers are collected at the electrodes. 我们报道了利用PCDTBT和PC70BM制备的BHJ太阳能电池，在AM 1.5G、功率为100mWcm-2的光照条件下测量：短路电流为10.6mA cm-2，开

16、路电压0.88v，填充因子FF为0.66，内量子效率接近100%，表明电池吸收的每一个光子都会产生一对载流子，电极收集了所有光生载流子。Titanium oxide optical spacer and hole blocking layer二氧化钛光空间与空穴阻挡层 Historically, a relatively low PCE has been demonstrated in polymer solar cells made from polymers that make use of the internal charge transfer concept, including P

17、CDTBT11,12. This low PCE has beenlimited by the relatively low photocurrent obtained from these devices. In BHJ cells, the photocurrent generation is governed by two main factors13,14: （i） the fractional number of absorbed photons in the active layer （relative to the total flux of photons from the s

18、olar spectrum） and （ii） the IQE defined by the fraction of collected carriers per absorbed photon. In principle, one can simply increase the thickness of the active layer to absorb more light. However, because of the relatively low carrier mobility of the disordered materials （cast from solution wit

19、h subsequent phase separation）, increasing the thickness increases the internal resistance of the device. Consequently, the fill factor typically plummets as the thickness is increased. Based on this simple analysis, we consider the following approach towards obtaining higher photocurrent: maximizin

20、g the photon absorption for a fixed active layer thickness while simultaneously improving the IQE. 以前，为解释聚合物太阳能电池相对低的能量转换效率利用内部电荷转移的概念，包括利用PCDTBT制作的BHJ 太阳能电池。这些器件相对较低的光电流导致了较低的能量转换效率。在BHJ太阳能电池中，光电流的产生主要受到两个因素影响：（i）活性层吸收的光子数（相当于吸收的光通量）和（ii）由每吸收一个光子产生的载流子数第一而来的内量子效率。原则上，可以简单的增加活性层的厚度以吸收更多的光。但是，由于无序材料（

21、）相对较低的载流子迁移率，增加厚度的同时会增加器件内部的电阻。因此，填充因子会随着厚度增加而大幅减小。基于这些分析，我们认为接下来的方法会提高光生电流：确定合适的活性层厚度以达到最大的光子吸收效率，同时提高内量子效率。 To increase the photocurrent while keeping the thickness fixed, we used an optical spacer between the photo-active layer and the top electrode; because of the optical spacer, the maximum lig

22、ht intensity is redistributed to be within the active charge separating BHJ layer. The utility of the optical spacer has been reproduced in recent publications15. In parallel, by choosing optimal conditions for processing, we have demonstrated a nanoscale BHJ morphology that results in nearly 100% I

23、QE. This dual focused approach applied to PCDTBT/PC70BM results in PCE, ne _ 6%; the highest value reported to date for polymer BHJ solar cells. 在确定适合的活性层厚度时为了增加光生电流，我们在光活性层和顶电极之间添加一个光空间。由于光空间的存在，光能够在BHJ太阳能电池的活性层中实现再分配。以往的文献中有用过光空间的。我们选择优化的制作调解，验证了纳米级别BHJ形貌的太阳能电池可以达到100%的内量子效率。这两种方法使得PCDTBT/PC70BMT太

24、阳能电池效率超过6%，这是目前报道的BHJ太阳能电池最高的效率。 Figure 1 shows the structure of the BHJ device together with the molecular structures and an energy level diagram of the component materials. From the fundamental physics of the open-circuit voltage associated with the donoracceptor heterojunction and the empirical r

25、elationship demonstrated in refs 1618, the relatively deep HOMO energy of PCDTBT, _5.5 eV, should result in a higher open-circuit voltage. Moreover, because the spherical symmetry of the fullerene has been lifted in PC70BM （compared to PCBM）, the PCDTBT/PC70BM BHJ material has higher absorption and,

26、 consequently,enhanced photocurrent. 图1是BHJ太阳能电池的结构、分子能级结构和组成器件的材料的能级图。从开路电压和给体-受体异质结的物理关系与在文献中证明的经验关系可以看出，PCDTBT相对低的HOMO能级使得开路电压提高。然而，由于PC70BM中没有球对称的结构（相对于PCBM），PCDTBT/PC70BM 材料的BHJ太阳能电池光吸收效率更高，从而提高了光生电流。 The solution processible titanium sub-oxide （TiOx） layer was introduced as an optical spacer21

27、 and as a hole blocker23 （see Supplementary Information） between the BHJ layer and the top metal electrode. The TiOx layer redistributes the light intensity within the BHJ by changing the optical interference between the incident light and the light reflected from the metal electrode24,25. As the ac

28、tive layer thickness decreases, the intensity of reflected light increases, and the optical interference effect becomes more pronounced. Hence, we expect that the efficacy of the TiOx layer will be higher for thinner active layers. Hole blocking by the TiOx is also more important for thinner-film de

29、vices. In the PCDTBT:PC70BM solar cells reported here, the thickness of the active layer is _80 nm, and the TiOx layer thickness is _10 nm. With this configuration, we are able to make good use of the optical spacer by avoiding destructive interference within the charge separating layer between the incident light and the light reflected from the aluminiumTiOx interface. In addition, the bottom of the conduction band of TiOx matches the LUMO of PC70BM. Finally, the relatively high electron mobility of PC70BM and the hole-blocking fea