Albes Tim, Gagliardi Alessio
Department of Electrical and Computer Engineering, Technical University of Munich, Karlstr. 45, 80333 Munich, Germany.
Phys Chem Chem Phys. 2017 Aug 9;19(31):20974-20983. doi: 10.1039/c7cp03513f.
In bulk-heterojunction organic solar cells the low permittivity in combination with the spatial and energetic disorder of the organic materials lead to a complex behavior of charge carriers within the active layer. Charges originate from exciton splitting at the heterojunction interface and the successive interplay between mutual Coulomb interactions and transport through the disordered organic can lead to insufficient separation from the interface, increased interface densities with respect to the bulk regions and, hence, affect recombination. To further understand the mechanisms of recombination, insight into the explicit spatial distribution of charge carriers within the blend is crucial. We performed kinetic Monte Carlo simulations on a bulk-heterojunction organic solar cell to assess the effect of Coulomb interactions and energetic disorder on the three-dimensional spatial distribution of charge carriers and highlight the correlation with both geminate and non-geminate recombination. We show that for materials with low permittivity and large energetic disorder the charge distribution is strongly inhomogeneous with accumulation along the heterojunction interface. In such cases recombination is not limited by recombination partners finding each other but rather an interface controlled process where geminate recombination dominates over nongeminate recombination.
在体相异质结有机太阳能电池中，低介电常数与有机材料的空间和能量无序性相结合，导致活性层内电荷载流子的行为复杂。电荷源自异质结界面处的激子分裂，相互库仑相互作用与通过无序有机材料的传输之间的连续相互作用可能导致电荷从界面的分离不足、相对于本体区域的界面密度增加，从而影响复合。为了进一步理解复合机制，深入了解共混物中电荷载流子的明确空间分布至关重要。我们对体相异质结有机太阳能电池进行了动力学蒙特卡罗模拟，以评估库仑相互作用和能量无序对电荷载流子三维空间分布的影响，并突出与双分子复合和非双分子复合的相关性。我们表明，对于具有低介电常数和大能量无序性的材料，电荷分布强烈不均匀，沿异质结界面积累。在这种情况下，复合不受复合伙伴相互找到对方的限制，而是一个界面控制的过程，其中双分子复合比非双分子复合占主导地位。
