聚合物太阳能电池中载流子复合与传输机制及器件特性的研究

发布时间：2018-01-07 12:05

本文关键词：聚合物太阳能电池中载流子复合与传输机制及器件特性的研究　出处：《北京交通大学》2014年博士论文　论文类型：学位论文

【摘要】：摘要：聚合物太阳能电池中的物理过程对器件效率的提升具有重要的指导意义,在聚合物：富勒烯器件中,载流子复合、传输及收集的分析对其光伏特性的改善是十分重要的；复合过程中给体受体界面处的电荷转移态(Charge Transfer State,CTS)复合与器件的开路电压(Voc)及短路电流(Jsc)直接相关；活性层与电极之间的界面修饰可以改善载流子的传输与收集,从而提高器件特性。本论文中,首先通过外量子效率光谱响应(EQE)及电致发光(EL)探测了聚合物太阳能电池的电荷转移态吸收与复合发光,发现除了给体材料和受体材料的EQE及EL特征外,出现了更低能量的CTS特征响应,且此CTS特征响应与给体材料和受体材料各自的最高占有轨道(HOMO)及最低未占有轨道(LUMO)能级差的变化趋势通常是相一致的。另外,利用精细平衡理论,研究了电荷转移态响应中EQE与EL的联系,通过EL光谱理论计算而得的EQE曲线与实际测量的曲线相吻合。随后通过电荷转移态EQE及EL计算了器件的理论开路电压值,计算的开路电压结果与实际测量的有一定差距,在0.3～0.45V之间,但是已经与实际结果接近。通过电致发光外量子效率(QLED)及特征能量(Ech)对开路电压的计算进行了修正,使得计算结果与实验值最大偏差缩小到0.15V左右。研究了不同外加电压(注入电流)下,器件CTS复合EL峰值位置的变化,发现实际测量到的EL峰值位置随注入电流的变化比理论分析值要小。其可能的原因为,靠近准费米能级处低能态的载流子不容易移动,需要通过去陷(detrapping)过程,抬高其中的一个电子或者空穴到更高的载流子可以自由移动的能级,移动之后与另外相应的载流子复合而发光。借助于电容-电压测试,研究了缓冲层对聚合物太阳能电池中载流子传输与复合的影响。介绍了聚合物太阳能电池中的电容-电压(C-V)特性,并从载流子传输及界面势垒两方面分析了其对C-V曲线的影响。研究了Mo03及NPB修饰层对器件特性的影响,适当厚度的修饰层可以改善器件的载流子传输和减小界面注入势垒,从而提高器件的短路电流及开路电压。过厚的修饰层增加器件串联电阻,阻挡载流子的注入与收集,引起载流子在器件内的大量复合。借助C-V测试研究了修饰层对载流子复合及收集的影响,适当厚度的修饰层改善载流子收集。初步研究了器件Voc与VCmax之间的关系,通过理论分析及实验我们发现,器件的Voc表示器件中的载流子复合与产生相等,VCmax表示载流子的复合超过电子在给体材料LUMO状态密度函数的积累,两者大小接近但存在差异。研究了聚合物太阳能电池中的界面复合及对器件特性的影响。首先,对比了双层结构与体异质结结构器件的J-V及QLED随注入电流的变化。由于双层结构不利于激子的解离,所以短路电流较体异质结的都小。研究了载流子迁移率对QLED的影响,实验发现材料的载流子迁移率越高,越可能发生电子与空穴在金属电极处的猝灭。初步研究了器件Jsc与QLED的关系,电荷转移态电致发光的QLED代表了电子空穴的复合程度,复合程度越小,被外电路所收集的载流子越多,EQE的值就会大,器件的短路电流越高(在不考虑材料的光响应范围的话)。值得注意的是,对于开路电压而言,需要器件中的辐射发光占全部复合过程比例越多越好,即希望大的QLED,但是对于器件的短路电流而言,需要器件中的载流子复合尽可能小,即小的QLED,所以对于器件的QLED,存在最佳值。
[Abstract]:Abstract: it is an important guiding significance to enhance physical processes in polymer solar cells on the efficiency of the device in the polymer: fullerene device, carrier recombination, analysis of the transmission and collection of improvement on the photovoltaic properties is very important; composite process to body body at the interface of the charge transfer state (the Charge Transfer State. CTS) and open circuit voltage composite device (Voc) and short circuit current (Jsc) directly related; interface modification between the active layer and the electrode can improve the transmission and collection of carriers, so as to improve the device characteristics.
In this paper, firstly, the external quantum efficiency of the spectral response (EQE) and electroluminescence (EL) charge detection of the polymer solar cell transfer state absorption and luminescence, found that in addition to the EQE and EL features of the body material and the receptor material, the lower energy CTS characteristic of the response, and the characteristics of CTS in response to the body material and the receptor material and their highest occupied molecular orbital (HOMO) and LUMO (LUMO) changes the energy level difference is usually consistent. In addition, by using the precise balance theory, the study of EQE and EL in response to the charge transfer state, EQE curve by EL spectroscopy and theoretical calculation consistent with the actual measurement curve. Then through the charge transfer state of EQE and EL open circuit voltage device theory calculation, there is a certain gap between the open circuit voltage calculation results and actual measurement, between 0.3 ~ 0.45V, but with the actual Results close. The external quantum efficiency by electro luminescence (QLED) and the characteristics of energy (Ech) to calculate the open circuit voltage is modified, the calculation result and the experimental value is reduced to about 0.15V. The maximum deviation of different applied voltage (current), change device CTS composite EL peak position, peak changes the location of the EL measured with the injected current value is much smaller than theoretical analysis. The possible reason for the carrier, near the Fermi level at low energy state is not easy to move, need to go through the depression (detrapping) process, raise one of the electrons or holes to higher carrier level can move freely. After moving with the addition of the corresponding carrier composite light.
With the help of capacitance voltage test of buffer layer on the carrier transport and recombination in polymer solar cells. The effects of introduced capacitance in polymer solar cell voltage (C-V) characteristics, and analyzes its influence on the C-V curve from the two aspects of carrier transport and interface barrier. The effects of Mo03 and effect of NPB modified layer the device characteristics, the proper thickness of the modified layer can improve the device carrier transmission and reduce the interface injection barrier, so as to improve the short-circuit current and open circuit voltage of the device. The thickness of the modified layer increases the series resistance of the device, blocking the carrier injection and collection, caused by the carrier in the inside of the device. A lot of composite effect of modification the layer recombination and collected by C-V test, modified layer thickness to improve the carrier collection. The relationship between Voc and VCmax devices were studied, through theoretical analysis and We find that the Voc of the device indicates that the carrier recombination is equivalent to that in the device. VCmax indicates that the recombination of carriers exceeds the accumulation of electron state density function of LUMO in the donor material, and the size of them is close but different.
Study on polymer solar cells in the composite interface and the device characteristics. First, comparing J-V and QLED devices with double layer structure of bulk heterojunction with the variation of current injection. Because the structure is not conducive to the double dissociation of exciton, so a short-circuit current of bulk heterojunction are small. The influence of the carrier mobility for QLED, materials found the carrier mobility is high, the more likely the quenching of electrons and holes in the metal electrode. The study on the relation between Jsc devices and QLED, the compound degree of charge transfer state of El QLED on behalf of the electron hole, the compound degree of smaller, more carriers are collected the external circuit, the EQE value will be higher, short-circuit current of the device (without considering the material light response range of words). It is worth noting that the open circuit voltage, the light emitting device to total radiation The more complex part is, the better it is, that is to say that the larger QLED is expected. However, for the short circuit current of the device, the carrier complex in the device is as small as possible, that is, a small QLED, so there is an optimum value for the QLED of the device.

【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM914.4

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