ИСТИНА

One of the potential alternatives to crystalline silicon solar cells is polymer solar cells (PSC) made of thin films based on polymer materials, which can be easily applied layer by layer onto flexible substrates of large area using wet processing methods. The use of organic materials gives such promising advantages as ease of processing, possible recyclability, and relatively low cost. For the widespread of polymer solar cells in daily practice, it is necessary to achieve a number of properties, such as the high power conversion efficiency, durability, and stability with prolonged exposure to temperature changes. When developing PSC, many polymeric materials need to be tested. The use of computer simulations can greatly facilitate the process of design and verification of the properties of various polymers prior to their experimental study. This report discusses the problems of design of computer models for simulations of the photoactive layer (PhL) of polymer solar cells. The fact is that the PhL is a nanocomposite in which π-conjugated (semiconducting) polymers are used as matrices. Due to π-π stacking interactions, crystalline domains, which play an important role in the formation of PhL properties, are present in the structure of conjugated polymers. However, at present, computer simulation methods have very limited possibilities for constructing models of polymeric materials, taking into account π-π interactions driving self-assembly processes. This problem is especially acute for mesoscopic methods that allow the study of polymeric materials at relatively large length and time scales. We propose a method for taking into account π-π stacking interactions in mesoscale models and check it in the framework of the dissipative particle dynamics method. We implement the dynamic bonding of mesoscopic particles in the model of conjugated polymer chains. As a prototype of polymer model, we use poly (3-hexylthiophene). We show that, taking into account π-π stacking interaction in our model leads to self-assembly of the polymer chains into large stacks with strong alignment due to the dynamic bonding. These stacks form lamellae, which is in good agreement with the known experimental data. The proposed methodology could be helpful in studies of conjugated polymer materials especially in design of PSC and other photovoltaic devices. We also constructed the reverse-mapping procedure that makes it possible to create models of atomistic samples of PhL based on the final states of the mesoscopic models. This creates possibilities to construct the multiscale schemes for simulation of the nanocomposites based on the conjugated polymers with various fillers to predict their thermophysical properties, the thermal stability.