A new cyano (−C[tbnd]N) free molecular design perspective for constructing carbazole-thiophene based environmental friendly organic solar cells

The construction of environmentally friendly organic solar cells (EFOSCs) is an emerging field of research. The OSCs constructed from famous end-capped acceptors 2-(6-oxo-5,6-dihydro-4H-cyclopenta [c]thiophen-4-ylidene)malononitrile (TC) and 1,1-dicyanomethylene-3-indanone (IC) are exhibiting high efficiencies. However, IC and TC are cyanides (−C[tbnd]N), and their synthesis is harmful to the environment. Reports demonstrated that replacing the toxic (−C[tbnd]N) with non-toxic (-CF₃, –SO₃H, –NO₂) is an expedient strategy for designing EFOSCs. Using reported strategy, nine carbazole-thiophene-based compounds (DTC1-DTC9) are proposed to make EFOSCs. Photovoltaic and optoelectronic potential of DTC1-DTC9 is confirmed through FMO, DOS, TDM, reorganization energy of the electron (λ_e), hole (λ_h), transport rate of electron (t_electron) and hole (t_hole), exciton-binding energy (E_b), transition energy (E_x), open-circuit voltage (V_oc), charge transfer with respect to PTB7-Th_donor:DTC_Acceptor complex and electron excitation analysis using DFT and TDDFT computations. The lower HOMO-LUMO gap (2.16 eV), E_x (1.81 eV), strong λ_max intensity (686.17 nm), high V_oc (1.85 V) and weak exciton-binding energy (0.14 eV) of DTC1-DTC9 than reference DTC specified that they have potential to absorb more solar energy and excitons are easier to separate into free charges. Charge transfer analysis proved the charge transfer from HOMO_PTB7-Th to LUMO_DTC-3 in PTB7-Th:DTC-3 blend. Consequently, proposed carbazole-thiophene-based novel compounds (DTC1-DTC9) are recommended for making EFOSCs with promising photovoltaic properties. This work can provide a new –C[tbnd]N free molecular design viewpoint in computational and experimental sciences for constructing high-performance environmental friendly OSCs.