It is well known that in organic solids the collision of two excitons can give rise to delayed fluorescence (DF). Revived interest in this topic is stimulated by the current endeavor towards the development of efficient organic optoelectronic devices such as organic light-emitting diodes (OLEDs) and solar cells, or sensitizers used in photodynamic therapy. In such devices, triplet excitations are ubiquitously present but their annihilations can be either detrimental, e.g., giving rise to a roll-off of intensity in an OLED, or mandatory, e.g., if the sensitizer relies on up-conversion of long-lived low-energy triplet excitations. Since the employed materials are usually noncrystalline, optical excitations migrate via incoherent hopping. Here, we employ kinetic Monte Carlo simulations (KMC) to study the complex interplay of triplet-triplet annihilation (TTA) and quenching of the triplet excitations by impurities in a single-component system featuring a Gaussian energy landscape and variable system parameters such as the length of the hopping sites, i.e., a conjugated oligomer, the morphology of the system, the degree of disorder (σ), the concentration of triplet excitations, and temperature. We also explore the effect of polaronic contributions to the hopping rates. A key conclusion is that the DF features a maximum at a temperature that scales with $\sigma /k_{B}T$. This is related to disorder-induced filamentary currents and thus locally enhanced triplet densities. We predict that a maximum for the TTA process near room temperature or above requires typically a disorder parameter of at least 70 meV.

中文翻译：

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共轭发光材料中三重-三重An灭的动力学蒙特卡洛研究

众所周知，在有机固体中，两个激子的碰撞会产生延迟荧光（DF）。当前对有效有机光电器件（例如有机发光二极管（OLED）和太阳能电池，或光动力疗法中使用的敏化剂）的开发引起了人们对这一主题的兴趣。在这样的设备中，三重激发无处不在，但是它们的an灭可能是有害的（例如，导致OLED中强度的下降），或者是强制性的（例如，如果敏化剂依赖于长寿命低能的上转换） -能量三重态激发。由于所使用的材料通常是非晶态的，因此光激发会通过非相干跳变迁移。这里，σ），三重态激发的浓度和温度。我们还探讨了极化子对跳跃率的影响。一个关键的结论是，DF在与温度成比例的温度下具有最大值$\sigma /{ķ}_{乙}Ť$。这与无序诱导的丝状电流有关，因此与三重态密度局部增强有关。我们预测，接近室温或高于室温的TTA过程的最大值通常需要至少70 meV的无序参数。