Designing spiro-bifluorene core-based promising molecules with enhanced optoelectronic attributes for high efficiency solar cell devices

Organic solar cells are green and cost-effective alternatives to fulfill the energy requirements of conventional energy sources. They have grabbed the attention of the research community owing to their good power conversion efficiency. The aim of present research work was to increase the efficiency of previously synthesised reference (R) molecule. For this, eight new X-shaped molecules were successfully designed by structural modifications of Spiro-OMeTAD. Structural modifications of R were made by using 9,9'-spirobifuorene as a core material with eight different end-capped acceptor moieties. Among different DFT-based functionals, MPW1PW91 functional with 6-31G (d,p) basis set was selected to determine the optoelectronic properties. Interestingly, all newly designed molecules had a smaller energy gap (Egap), lower excitation energy (Ex) and greater absorption maxima (λmax) which illustrated the superior potential of the designed molecules (X1 to X8) than R. Among different molecules, X4 showed the most appropriate frontier molecular orbitals with the highest λmax (592.74 nm), best fill factor (86.43%), greater power conversion efficiency (10.04), improved open circuit voltage (0.83 eV) and the least Ex (2.09 eV). All newly created molecules showed better results than R, elucidating the potential of these modified Spiro-OMeTAD-based hole transport materials as pioneering materials in the fabrication of efficient next-generation SCs devices.