Computational prediction of the properties of bis(ethynylthienyl)dialcoxynaphthalene-based conjugated polymers for organic solar cell applications

A series of homo- (P0) and copolymers (P1-P5) based on the electron-donor building-block 2,2′-(2,3-bis(2-ethylhexyloxy)naphthalene-1,4-diyl)bis(ethyne-2,1-diyl)dithiophene (1,4-NET) including ethynyl linkers aiming to promote coplanarity were designed, and their properties predicted using theoretical methodologies to evaluate their potential in organic solar cell applications. The geometries, FMO levels, energy bandgaps, and absorption spectra of trimer models were determined using time-dependent density functional theory, while their photovoltaic and charge-transport properties were estimated by the Scharber's model and semiclassical Marcus theory, respectively. Compared to high-performance conjugated polymers (CPs), such as PTB7-Th or PM6, and similar systems based on the 1D-BDT unit, the HOMO and LUMO levels of P0-P5 tend to be higher. In addition, the new CPs have complementary absorptions with narrow-bandgap acceptors, such as ITIC and Y6, and adequate matches between their HOMO and LUMO levels. Although the simulated photovoltaic and charge-transport properties could be overestimated, the best candidate to be synthesized and tested in organic solar cells is P5 due to its suitable and well-balanced properties, demonstrating the positive effect of incorporating ethynyl bridges to improve the optoelectronic properties of CPs.