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Buildup of Triplet-State Population in Operating TQ1:PC71BM Devices Does Not Limit Their Performance
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2020-03-23 , DOI: 10.1021/acs.jpclett.0c00756
Safakath Karuthedath 1 , Julien Gorenflot 1 , Armantas Melianas 2 , Zhipeng Kan 1 , Martijn Kemerink 3 , Frédéric Laquai 1
Affiliation  

Triplet generation in organic solar cells has been considered a major loss channel. Determining the density of the triplet-state population in an operating device is challenging. Here, we employ transient absorption (TA) spectroscopy on the quinoxaline–thiophene copolymer TQ1 blended with PC71BM, quantify the transient charge and triplet-state densities, and parametrize their generation and recombination dynamics. The charge recombination parameters reproduce the experimentally measured current–voltage characteristics in charge carrier drift-diffusion simulations, and they yield the steady-state charge densities. We demonstrate that triplets are formed by both geminate and nongeminate recombination of charge carriers and decay primarily by triplet–triplet annihilation. Using the charge densities in the rate equations describing triplet-state dynamics, we find that triplet-state densities in devices are in the range of charge carrier densities. Despite this substantial triplet-state buildup, TQ1:PC71BM devices exhibit only moderate geminate recombination and significantly reduced nongeminate charge recombination, with reduction factors between 10–4 and 10–3 compared to Langevin recombination.

中文翻译:

运行中的TQ1:PC 71 BM设备中的三重态人口聚集不会限制其性能

有机太阳能电池中的三重态产生被认为是主要的损耗通道。确定操作装置中三重态种群的密度具有挑战性。在这里,我们对掺入PC 71的喹喔啉-噻吩共聚物TQ1采用瞬态吸收(TA)光谱BM,量化瞬态电荷和三重态密度,并参数化它们的产生和重组动力学。电荷复合参数在载流子漂移-扩散模拟中重现了实验测量的电流-电压特性,并产生了稳态电荷密度。我们证明三元组是由电荷载流子的重组和非重组形成的,而衰变主要是由三重态-三重态an灭。使用描述三重态动力学的速率方程式中的电荷密度,我们发现器件中的三重态密度在电荷载流子密度范围内。尽管存在大量的三重态,TQ1:PC 71BM装置仅表现出中等的geem重组,而非gege的电荷重组显着减少,与兰格文重组相比,还原因子在10 –4到10 –3之间。
更新日期:2020-04-24
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