有机小分子太阳能电池的界面研究

【作者】 宋群梁；

【导师】 侯晓远；

【作者基本信息】 复旦大学 ， 凝聚态物理， 2006， 博士

【摘要】 我们选用了小分子体系来研究了有机太阳能电池界面发生的基本物理过程以及界面对其性能的影响，主要进行了以下几方面的研究： 1．受体材料和阴极之间插入缓冲层对有机小分子太阳能电池的性能的影响 我们通过引入新的Alq₃缓冲层来替代以前被广泛使用的BCP缓冲层，将未封装的有机太阳能电池的寿命提高了约150倍，而且能量转换效率还有所改善。对于这层Alq₃缓冲层的作用，我们提出了与以往不同的观点，即该缓冲层可能不主要是激子阻挡的作用，而是在沉积金属阴极的时候阻挡金属原子向受体材料的扩散，在器件取出真空腔体后阻挡水、氧向受体材料的扩散。这样的观点很好地解释了我们的实验结果，而且其它一些辅助实验也进一步证实了我们自己的观点。 2．理论和实验的对比研究来考察干涉效应在有机多层膜结构中的影响 有机太阳能电池是一种具有多层膜结构的光电转换器件。在薄膜多层器件中，干涉效应是必须考虑的。光在有机多层膜中的重新分布直接影响光在有机材料中的吸收和激子的产生，最终影响到可获得的自由载流子的量。我们采用传输矩阵的计算方法计算了考虑干涉效应后的多层膜的紫外-可见吸收光谱，与实验得到的测量结果相对比，获得了很好的一致性，而与认为光是指数衰减的计算结果的差异很大。这样我们就比较直接地证明了光的干涉作用在有机多层膜中确实存在。进一步的计算结果表明，适当的膜厚度的选择和结构的选择能够使光在激子拆分的界面附近的吸收发生数倍的变化。 3．采用瞬态光电压技术研究有机太阳能电池中激子的拆分过程。 我们采用瞬态光电压的办法来测量了在两个电极上产生的光电压随时间的变化关系，得到了极性发生转变的瞬态光电压。利用激子在金属＼有机界面的拆分效应和载流子在内建电场的作用下被分离的共同作用，我们很好地解释了实验所观测到的现象。我们从实验上证实了激子在界面被有效拆分的物理过程的存在并对界面拆分激子对测量结果的影响进行了估计，并据此提出了在设计高效有机太阳能电池中应该注意的原则。更多还原

【Abstract】 The fundamental physics processes at the interfaces in organic solar cells and the effect of these interfaces on the performance of organic solar cells has been studied for small molecule system. Our effort focused on three parts:1. The effect of a buffer layer between acceptor and the cathodeBy introducing a new thin buffer layer of Alq₃ between acceptor(C₆₀)and the cathode to substitute the widely used BCP buffer, the lifetime of small molecule organic solar cells was improved about 150 times for unencapsulated devices. The power conversion efficiency was not decreased and was even a little improved. We have proposed that the thin buffer blocks metal atom diffusion into the organic film during fabrication of devices and blocks oxygen/water diffusion after the devices are removed from the vacuum. This process is quite different from the role of exciton blocking, and can be used to explain the results we obtained. Further experiments showed that our proposal is correct.2. Theoretical and experimental assessment of the interference effect in multiple organic thin layersOrganic solar cells are multiple thin layer optoelectronic devices, and the interference effect in multiple thin layers must be taken into account. Because of this interference effect, the incident light in organic thin films is redistributed. This redistribution of light will have a direct effect on the light absorption and the following exciton production and on the number of final free carriers that are collected by electrodes. By using the transfer matrix calculation of light propagation in layered organic thin films, the interference effect is taken into account, and the UV-Vis absorption spectrum of these thin films can be obtained. While there is a large discrepancy between the experimental results and the calculation based on exponential decay law, good agreement is found when comparing the transfer matrix-calculated results with those experimental ones, showing that the interference effect does play its role. Further calculation based on transfer matrix method showed that by appropriate selection of the thickness of the organic films and the structure of organic solar cells, the absorption at the interface, where the excitons are dissociated, can be enhanced several times.3. Exciton dissociation at interfaces studied by transient photovoltage techniqueThe photovoltage versus the time between two electrodes was measured by transient photovoltage technique, and an abnormal polarity change of transient photovoltage was observed. By using the interfacial dissociation at the metal\organic interface and the separation of free carriers under the force of the internal electric field, the obtained results could be explained. Thus we have experimentally verified the existence of interfacial dissociation of exciton. The effect of such interfacial dissociation on the measured photovoltage was estimated, and design rules for high power conversion efficiency organic devices were proposed.更多还原