# Generalized Kinetic Monte Carlo Framework for Organic Electronics
## 1 Introduction  
Organic semiconductors represent a promising candidate for cost-efficient, environmentally-friendly materials and renewable energy conversion devices. The advantage compared to currently widely-used inorganic semiconductor-based devices is captured in their mechanical flexibility, light weight and electrical and optical controllability at the molecular level. Organic semiconductors have exhibited a considerable potential for application in organic thin-film transistors (OTFT) [1], light-emitting diodes (OLEDs) [2] and solar cells (OSCs) [3, 4]. Experimental research on organic-based devices is accompanied by computational methods providing a better understanding of the underlying processes in energy conversion devices made from nanostructured organic materials. In the simulation of organic materials and devices, several methods on different length scales are of interest. While drift-diffusion (DD) simulations yield a good understanding at a macroscopic continuum level of several \(\mu\)m, they can neither provide insight into the microscopic, internal properties, nor track the particle dynamics. Tools solving molecular dynamics give detailed insight into the processes occurring on an atomistic length scale (\(\leq 1\,\)nm), but the computational demand is not feasible for the simulation of bulk materials or thin films of a \(100\,\)nm thickness. Kinetic Monte Carlo (kMC) simulations have gained more and more attention in the field of materials science in recent years. Due to strong localization of charge carriers on molecules or molecular subunits, kMC is highly feasible for the modeling of organic disordered semiconductors. The aim of understanding the internal processes in organic devices and the rising available computational power has driven the development of the above microscopic numerical methods. Existing kMC models can reproduce the main macroscopic characteristics of organic optoelectronic devices and provide insight intofundamental physical properties considering charge transport and optical processes. Thus, kMC provides a bridge between different length scales from the atomistic level up to a macroscopic device level. [PERSON] and [PERSON] have presented one of the first applications of kMC in the study of charge transport in organic materials [5]. From that point on, kMC has been employed for many theoretical studies covering charge and exciton transport [6; 7; 8], recombination of charge carriers [9; 10] and the impact of all processes on the photocurrent generation [11; 12; 13; 14; 15]. kMC simulations have been frequently utilized to study full devices such as bulk-heterojunction (BHJ) organic solar cells [10; 11; 12; 13; 15; 16]. There are several groups working on kMC models describing all properties mentioned above to a certain extent. Many of them consist of a cubic lattice model, which cannot represent all geometrical features and the impact of the structure of organic materials on the physical processes. Furthermore, many do not consider the directionality of charge transport along, e.g., polymer chains. Another limitation of existing models is the simplified treatment of excitonic processes, which are of high importance regarding organic devices. Most kMC models either account for singlet [10; 17; 18; 19] or triplet exciton dynamics [20; 21; 22; 23] for the use in OSCs or OLEDs, respectively. However, the interplay between singlets and triplets can be used to modify exciton lifetimes and diffusion lengths, which is a promising way to tailor efficiencies in organic devices and therefore requires a better understanding [24; 25; 26]. In this work, we present our in-house-developed generalized kMC framework for the simulation of organic semiconductors and devices. Our model overcomes the mentioned limitations by the inclusion of a non-cubic lattice model, based on the Voronoi tessellation, and a model of polymer chains. Both yield a better geometrical description of organic materials and herewith provide new insight into the electrical properties.