Derivation and solution of effective medium equations for bulk heterojunction organic solar cells
Derivation and solution of effective medium equations for bulk heterojunction organic solar cells
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DOI：
10.1017/s0956792516000541
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发表时间：
2017-01
影响因子：
1.9
通讯作者：
G. Richardson;C. Please;V. Styles
中科院分区：
文献类型：
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作者：
G. Richardson;C. Please;V. Styles
本文建立了有机体异质结太阳能电池中电荷输运的漂移扩散模型，该电池是由连接的受体和施主材料夹在两个电极之间形成的。该模型解释了(i)激子的大量光产生，（ii）激子漂移和复合，（iii）受体-给体界面上激子解离（成极化子），（iv）极化子复合，(v)极化子解离成自由电子（在受体中）和空穴（在给体中），（vi）电子/空穴传递和（vii）受体-给体界面上的电子-空穴复合。采用有限元法求解具有高度复杂受体/供体界面的细胞模型。这些解表明，在物理参数真实的情况下，在发电状态下，解在微观结构的尺度上变化很小。这促使我们在微观结构上进行均匀化；这个过程在细胞尺度上产生了一个简单得多的一维有效介质模型。全模型的解和有效介质（均质）模型的解之间的比较在施加电压小于内置电压（发电状态）时非常有利，但当施加电压高于内置电压时就失效了。此外，值得注意的是，均质化技术提供了一种系统的方法，将体异质结的有效介质建模[19,25,36,37,42,59]与一种更基本的方法联系起来，这种方法可以明确地模拟整个微观结构[8,38,39,58]，并且它允许根据微观结构的几何形状推导有效介质模型中的参数。最后，利用有效介质模型研究了改变具有交错受体/供体界面的器件的微观结构几何形状对其电流-电压曲线的影响。
A drift-diffusion model for charge transport in an organic bulk heterojunction solar cell, formed by conjoined acceptor and donor materials sandwiched between two electrodes, is formulated. The model accounts for (i) bulk photogeneration of excitons, (ii) exciton drift and recombination, (iii) exciton dissociation (into polarons) on the acceptor–donor interface, (iv) polaron recombination, (v) polaron dissociation into a free electron (in the acceptor) and a hole (in the donor), (vi) electron/hole transport and (vii) electron–hole recombination on the acceptor–donor interface. A finite element method is employed to solve the model in a cell with a highly convoluted acceptor/donor interface. The solutions show that, with physically realistic parameters, and in the power generating regime, the solution varies little on the scale of the micro-structure. This motivates us to homogenise over the micro-structure; a process that yields a far simpler one-dimensional effective medium model on the cell scale. The comparison between the solution of the full model and the effective medium (homogenised) model is very favourable for applied voltages less than the built-in voltage (the power generating regime) but breaks down as the applied voltages increases above it. Furthermore, it is noted that the homogenisation technique provides a systematic way to relate effective medium modelling of bulk heterojunctions [19, 25, 36, 37, 42, 59] to a more fundamental approach that explicitly models the full micro-structure [8, 38, 39, 58] and that it allows the parameters in the effective medium model to be derived in terms of the geometry of the micro-structure. Finally, the effective medium model is used to investigate the effects of modifying the micro-structure geometry, of a device with an interdigitated acceptor/donor interface, on its current–voltage curve.