Roland Steffen, Kniepert Juliane, Love John A, Negi Vikas, Liu Feilong, Bobbert Peter, Melianas Armantas, Kemerink Martijn, Hofacker Andreas, Neher Dieter
Department of Physics and Astronomy , Universität Potsdam , 14476 Potsdam , Germany.
Molecular Materials and Nanosystems, Department of Applied Physics , Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven , The Netherlands.
J Phys Chem Lett. 2019 Mar 21;10(6):1374-1381. doi: 10.1021/acs.jpclett.9b00516. Epub 2019 Mar 11.
We employed bias-assisted charge extraction techniques to investigate the transient and steady-state recombination of photogenerated charge carriers in complete devices of a disordered polymer-fullerene blend. Charge recombination is shown to be dispersive, with a significant slowdown of the recombination rate over time, consistent with the results from kinetic Monte Carlo simulations. Surprisingly, our experiments reveal little to no contributions from early time recombination of nonequilibrated charge carriers to the steady-state recombination properties. We conclude that energetic relaxation of photogenerated carriers outpaces any significant nongeminate recombination under application-relevant illumination conditions. With equilibrated charges dominating the steady-state recombination, quasi-equilibrium concepts appear suited for describing the open-circuit voltage of organic solar cells despite pronounced energetic disorder.
我们采用偏置辅助电荷提取技术，研究了无序聚合物 - 富勒烯共混物完整器件中光生电荷载流子的瞬态和稳态复合情况。结果表明电荷复合具有色散性，复合速率随时间显著减慢，这与动力学蒙特卡罗模拟的结果一致。令人惊讶的是，我们的实验表明，非平衡电荷载流子的早期复合对稳态复合特性几乎没有贡献。我们得出结论，在与应用相关的光照条件下，光生载流子的能量弛豫速度超过了任何显著的非成对复合速度。由于平衡电荷主导稳态复合，尽管存在明显的能量无序，准平衡概念似乎适用于描述有机太阳能电池的开路电压。
