Multiscale modeling of active layer of hybrid organic-inorganic solar cells for photovoltaic applications by means of density functional theory and integral equation theory of molecular liquids

Abstract

Photovoltaic devices convert solar energy into electricity and are promising candidates to reduce carbon emission while providing an alternative way to meet increasing demand in energy consumption. In recent years, organic or hybrid organic-inorganic photovoltaic devices demonstrate steady increase in performance and stability and a promising tendency toward the low production cost. To make them attractive for commercial production, however, a deep understanding and ability to predict physical, chemical and electrochemical processes occurring in photovoltaic conversion layer is needed. Here, we present multiscale modeling of electronic and structural properties of hybrid organic-inorganic perovskites (OIP) of the type CH3NH3PbX3, X = Br, Cl, I, in contact with organic molecules of P3BT, P3HT, or SQ02, including adsorption on inorganic substrates of TiO2. Our methodology is based on Density Functional Theory (DFT) and integral equation theory of molecular liquids in the Reference Interaction Site Model (RISM). We apply it to study the photovoltaic thin film nanomorphology and determine the key factors affecting the performance of OIP-based bulk heterojunction solar cells through their influence on charge separation, charge transport and recombination losses in donor-acceptor blends. These factors include chemical composition of heterojunctions and mutual orientation of molecules on the border of the donor-acceptor or donor-acceptor-substrate systems. Since the formation of thin active layer of solar cells occurs in fluidic phase, we also provide a detailed microscopic insight into the organization of solvent molecules in the solvation shell structure and their contribution to the solvation thermodynamics. In total, these properties define charge transfer processes from donor to acceptor and are utilized in development of new generation organic and hybrid organic-inorganic solar cells. The calculated nanoscale morphologies serve as a guide in rational design of organic or hybrid photovoltaics.