Molecular engineering with benzothiophene based bracing units to improve the photovoltaic properties of the naphthalene core based chromophores

A series of fused naphthalene-based chromophores (PT1-PT7) with an A-π-A configuration was designed through reference compound (PTR) for photovoltaic materials. Structural tailoring was done by incorporating benzothiophene (BT) based acceptor groups at the peripheral positions. Quantum chemical calculations were accomplished at MPW1PW91/6-31(d, p) functional to explore the fundamental photovoltaic and electronic characteristics of newly designed chromophores. Structural modeling with efficient BT-based acceptors had marked an impact on the absorption spectra across all derivatives, leading to a reduction in band gaps. The PT1-PT7 compounds displayed a band gap in the span of 2.267 to 2.137 eV, and broader absorption spectra of 685.109 to 718.666 nm in chloroform. The significant exciton dissociation rate was investigated for entitled compounds due to their smaller binding energy values (E_b = 0.492-0.368 eV). Furthermore, density of states (DOS) and transition density matrix (TDM) maps confirmed efficient transfer of charge from π-spacer in HOMO to BT acceptors in LUMO. In all the designed compounds PT5 displayed the narrowest band gap (2.137 eV), the highest bathochromic shift (718.666 nm), and the lowest E_b (0.492 eV), illustrating suitable candidate for photovoltaic materials. Moreover, open-circuit voltage (V_oc) analysis was conducted with respect to HOMO_DONOR and LUMO_PC61BM. All the designed derivatives are estimated to exhibit notable PCEs with good FF values. Thus, these findings illustrated that molecular engineering through BT based acceptors could be utilized as efficient technique for obtaining significant photovoltaic materials.