Molecular description of charge transport in the IDIC non-fullerene acceptor for organic solar cells

Non-fullerene acceptors (NFAs) have demonstrated remarkable performance when used in bulk heterojunction organic solar cell devices. Their exceptional properties, such as the ability to tune their electronic properties by chemical modifications, increased absorption in the visible and near infrared part of the spectrum, and general ease of synthesis, make them a key alternative for traditional fullerene-based acceptors. IDIC is a typical NFA material having a five-membered fused ring core and strong electron withdrawing end groups. In this work we use a multiscale computational approach based on a hopping model and Marcus’ charge transport theory to investigate electron and hole transport in crystal and amorphous IDIC samples. The basic transport parameters, namely reorganization energy, electronic couplings and site energies are calculated and compared with the corresponding values for fullerene-based acceptors where available in the literature. Electrostatic and induction contributions to the total energetic disorder are also examined and discussed. Using Kinetic Monte Carlo simulation, the electric field and temperature dependence of mobility is systematically evaluated for electrons and holes, and the data are fitted against the widely used Gaussian Disorder Model. We find that compared to the commonly used PCBM fullerene acceptor, IDIC has larger reorganization energy and similar energetic disorder. However, it exhibits comparable electron mobility, due to enhanced electronic couplings with neighboring molecules in the crystalline brickwork-like structure.