Effects of edge substitution of subazaphenalenephthalocyanine with electron withdrawing and/or donating groups on electronic and optical properties: A DFT/TDDFT study

Abstract

Subphthalocyanine (subPC), a phthalocyanine homologue, is a popular material in organic solar cells (OSCs). However, due to its inherent disadvantage of limited absorption, the power conversion efficiency (PCE) of subPC based OSC is restricted. Subazaphenalenephthalocyanine (subAPPC), a core expanded derivative of subPC, has been synthesized, and it shows great potential because of its broad absorption spectrum in the visible region. In this paper, we model a series of subAPPC derivatives through the substitutions of peripheral hydrogen atoms with different electron donating and/or withdrawing groups. Density functional theory (DFT) and time dependent DFT are utilized to systematically study the effects of substitutions of electron donating groups (-C(CH3)3 and –CH3), electron withdrawing groups (-Cl and –NO2), and their combinations on physical and optical properties. The calculation results indicate that subAPPC–NO2–4C(CH3)3 has an appropriate dipole moment, low exciton binding energy, and strong absorption strength among subAPPC derivatives, and may be a promising donor material. In addition, subAPPC-5NO2 may be a good electron acceptor material because with respect to popular C60 it has appropriate energy level, lower exciton binding energy, and much higher absorption strength in the visible region. Last but not least, the introduction of –NO2 group may better improve the performance of OSC materials than that of popular -Cl.